Type 2 Diabetes

Type 2 diabetes is a chronic metabolic disorder in which the body either resists the action of insulin or fails to produce enough of it, so that glucose stays elevated in the blood. It accounts for the large majority of cases of diabetes mellitus, distinguishing it from type 1 diabetes, an autoimmune destruction of insulin-producing cells. Its development is usually gradual and is closely tied to excess body fat, age, inherited susceptibility and physical inactivity, so it is often diagnosed only after years of silent hyperglycemia. Because it can damage the heart, blood vessels, kidneys, nerves and eyes, it is a leading cause of illness and premature death, and it has become one of the most significant noncommunicable diseases in the world.

This entry first explains how the condition is defined and diagnosed, then describes its underlying physiology, in which insulin resistance, failing pancreatic beta cells, hormones from several organs and chronic low-grade inflammation interact. It goes on to cover genetic and environmental risk factors, the global distribution and projected growth of the disease, its clinical presentation, and the acute and chronic complications that follow. The later sections address prevention, glycemic targets and monitoring, lifestyle and pharmacological treatment, the management of cardiovascular and kidney risk, care for special populations, public-health and economic burden, the historical development of current knowledge, and the questions that remain open.

Definition and Diagnostic Criteria

Type 2 diabetes is diagnosed when hyperglycemia is persistent and reaches levels defined by laboratory thresholds. No single symptom or reading is used on its own in routine practice. The American Diabetes Association (ADA) accepts four routes to diagnosis: A1c ≥6.5%, fasting glucose ≥126, 2-hour OGTT ≥200, or random glucose ≥200 with symptoms.

Glucose-based thresholds

Fasting plasma glucose is measured after at least eight hours without eating, and a diagnosis requires a value of 126 mg/dL (about 7.0 mmol/L) or higher. The 2-hour test uses a standard 75-gram glucose solution, and a value of 200 mg/dL or higher indicates diabetes. A random reading is used only when the patient has classic symptoms of high blood glucose such as increased thirst and frequent urination. Although the oral glucose tolerance test (OGTT) is more sensitive and specific than the fasting test, the ADA notes that its poor reproducibility and difficulty to perform in practice keep it out of routine clinical use.

Confirmation is part of the process. Confirmation requires repeat testing on a separate day unless the patient has unambiguous hyperglycemic symptoms. When tests disagree, clinicians rely on the more direct glucose measurements. One cohort of 5,764 adults without known diabetes found that the sensitivity of HbA1c ≥ 6.5% was only 43.3% compared to the FPG criterion and 28.1% compared to the 2hPG criterion. The authors therefore advised that FPG and/or 2hPG should be obtained whenever an HbA1c result leaves the diagnosis in doubt.

Prediabetes

Prediabetes is defined by three overlapping categories. Impaired fasting glucose (IFG) is a fasting value of 100–125 mg/dL, and impaired glucose tolerance (IGT) is a 2-hour OGTT value of 140–199 mg/dL. HbA1c values of 5.7–6.4% fall into the same band. The bounds are not identical across guidelines: WHO opted to keep its upper limit of normal at under 110 mg/dL for fear of causing too many people to be diagnosed as having impaired fasting glucose, whereas the ADA lowered the upper limit of normal to a fasting plasma glucose under 100 mg/dL.

The two categories reflect different defects. Raised hepatic glucose output and a defect in early insulin secretion were characteristic of impaired glucose tolerance, whilst peripheral insulin resistance was characteristic of impaired fasting glucose, according to an ADA follow-up report cited in one review. People in these categories carry a significant risk of developing Diabetes, which is why they are a central target for prevention. Not every person with prediabetes progresses to diagnosed diabetes, and the risk varies with age, weight, and ancestry.

Glycated hemoglobin (HbA1c)

HbA1c measures the fraction of hemoglobin that has become glycated. Because red blood cells circulate for roughly 90 to 120 days, the value measures your average blood glucose for the past two to three months. A major practical advantage is that it does not require fasting.

The test assumes normal red-cell turnover and normal hemoglobin structure, and several conditions violate those assumptions. Iron deficiency anaemia, vitamin B12 or folate deficiency, splenectomy, and sometimes chronic kidney disease can produce falsely high values, while haemolytic anaemia, recent blood transfusion, sickle cell disease, EPO therapy, and pregnancy can produce falsely low values. Hemoglobin variants add a further problem: HbS, HbC, HbE, and HbD can cause falsely low or high HbA1c results by altering glycation sites, shortening red cell lifespan, or causing co-elution on chromatography-based assay platforms. Assay method matters as well, since the depending on the assay method used and the type of hemoglobin abnormality present can shift results in either direction.

The consequences can be serious. In one case report, a 63-year-old woman with sickle cell disease and alpha thalassemia presented with a glucose of 609 mg/dL and diabetic ketoacidosis, yet her HbA1c level was 4.8%. In pregnancy, HbA1c is generally not used to diagnose gestational diabetes, because HbA1c underestimated the degree of glucose intolerance in the late second trimester. The UK guideline NICE NG28 therefore explicitly excludes HbA1c as a diagnostic tool in pregnancy, suspected type 1 diabetes, haemoglobin variants, and several other clinical situations. In those settings, alternative tests include fasting plasma glucose, random plasma glucose, oral glucose tolerance test (OGTT), fructosamine, and continuous glucose monitoring (CGM).

Differentiation and Classification of Diabetes

Classification matters because it determines therapy, yet a meaningful minority of people cannot be placed cleanly into one category at diagnosis. Type 1 and type 2 diabetes are heterogeneous diseases in which clinical presentation and disease progression may vary considerably. Classification is important for determining therapy, but some individuals cannot be clearly classified as having type 1 or type 2 diabetes at the time of diagnosis. The ADA framework separates type 1 diabetes from type 2 diabetes, with the former due to autoimmune b-cell destruction, usually leading to absolute insulin deficiency, and the latter due to a progressive loss of adequate b-cell insulin secretion frequently on the background of insulin resistance.

Distinguishing Type 1 from Type 2

Clinicians combine several features rather than relying on any single one. Type 1 diabetes typically develops during childhood, manifesting with an acute onset (e.g., diabetic ketoacidosis), whereas type 2 diabetes is much more common, has a strong genetic component, and is associated with obesity and a sedentary lifestyle. Age alone is an unreliable guide, since adults can have either condition. The most informative laboratory tools are islet autoantibodies and C-peptide, a marker of the insulin the pancreas is still secreting. Autoantibody-positive disease points toward an autoimmune process driven by autoimmunity, while low C-peptide indicates that insulin-producing beta cells have been substantially lost. Type 2 diabetes is usually associated with preserved or even elevated C-peptide.

Latent Autoimmune Diabetes in Adults

Latent autoimmune diabetes in adults (LADA) is the main source of diagnostic confusion. LADA is a slowly progressive form of autoimmune diabetes characterized by the presence of islet autoantibodies, gradual β-cell decline, and clinical onset in adulthood. Its presentation resembles type 2 diabetes, so it is often misdiagnosed because of a lack of both awareness and standardized diagnostic criteria. The most common marker is antibody against glutamic acid decarboxylase (GAD65), which is present in 70%-90% of cases; IA-2 and ZnT8 antibodies are also used. Because beta-cell destruction is slower, patients may initially manage with oral agents, but not all patients with type 2 diabetes require insulin, but all patients with LADA will gradually progress to insulin dependence. Early antibody testing is therefore important: the earlier insulin therapy is initiated, the greater the preservation of pancreatic beta cells. Some authors argue that LADA is better regarded as a form of type 1 diabetes, and the naming remains debated.

Monogenic and Secondary Forms

Monogenic diabetes, most often maturity-onset diabetes of the young (MODY), results from single-gene defects that impair beta-cell function. MODY arises from pathogenic variants in genes that regulate beta-cell function, insulin secretion, or glucose sensing, and these are inherited in an autosomal dominant pattern. The subtypes differ considerably in course. For example, GCK-related MODY is stable, nonprogressive elevated fasting blood glucose; typically does not require treatment, while HNF1A-related forms show a progressive reduction in endogenous insulin production but exhibit marked sensitivity to sulfonylureas. Estimates of prevalence vary, but monogenic defects that cause b-cell dysfunction, such as neonatal diabetes and MODY, represent a small fraction of patients with diabetes (<5%). Because studies suggest that 50–90% of MODY cases are erroneously classified as type 1 or type 2 diabetes, the value of genetic testing lies largely in avoiding inappropriate treatment.

Secondary diabetes arises from another identifiable cause. Recognized categories include pancreatic disease; hormonal abnormalities other than primary lack of insulin action (e.g., Cushings disease, Acromegaly, Phaeochromacytoma); drug or chemical induction. Examples in current guidance include diseases of the exocrine pancreas (such as cystic fibrosis), and drug- or chemical-induced diabetes (such as with glucocorticoid use, in the treatment of HIV/AIDS, or after organ transplantation). Secondary causes can also unmask a pre-existing predisposition, and the appearance of abnormal glucose metabolism alongside them does not necessarily indicate the presence of underlying diabetes although in many cases a mild asymptomatic, primary diabetes may be made overt by the secondary illness.

Ambiguity and Reclassification

Some patients never fit neatly. One group is commonly non-obese and have reduced insulin secretory capacity that is not sufficient to make them ketosis prone. Many initially respond to oral agents but, with time, require insulin. Some appear to have a slowly evolving form of type 1 diabetes, whereas others defy easy categorization. For this reason, the ADA specifies that although difficulties in distinguishing diabetes type may occur in all age-groups at onset, the diagnosis becomes more obvious over time in people with b-cell deficiency. Reclassification is thus a longitudinal process, relying on repeated C-peptide measurements, reassessment of insulin requirements, and genetic testing when the course is atypical. Pregnancy adds a further layer: women diagnosed with diabetes in the first trimester should be classified as having preexisting pregestational diabetes, while GDM is diabetes that is first diagnosed in the second or third trimester of pregnancy that is not clearly either preexisting type 1 or type 2 diabetes.

Insulin Resistance and Beta-Cell Failure

Type 2 diabetes arises from two linked defects: tissues that respond poorly to insulin, and pancreatic beta cells that eventually cannot make enough of it. Their relative weight has been debated for decades. Current work treats them as parts of one feedback loop, in which a fall in insulin sensitivity drives the beta cell to secrete more, and a failing beta cell then removes the margin that kept glucose normal.

Insulin resistance

In insulin-resistant states, insulin signalling is weakened in the three main target tissues. In skeletal muscle, less glucose enters the cell after a meal, so more of it stays in the blood. In adipose tissue, insulin fails to suppress lipolysis, which releases free fatty acids into the circulation. In the liver, insulin no longer adequately restrains glucose production, so gluconeogenesis and glucose output continue even when blood glucose is already high. Visceral fat appears to be a major driver of this resistance, and the contribution of ectopic fat in muscle and liver is a central part of the picture. Fat stored outside adipose tissue, sometimes called lipotoxicity, adds to the problem by interfering with insulin action in the liver and muscle.

Compensatory hyperinsulinemia

Early on, the beta cell compensates. Insulin secretion rises in proportion to the loss of sensitivity, so that the product of insulin sensitivity and first-phase insulin release, known as the disposition index, stays roughly constant. Because of this, people with early type 2 diabetes often have raised rather than low insulin levels, and their glucose remains close to normal. The compensation depends on beta-cell plasticity: the cells enlarge, proliferate and increase their output per cell. Some studies also suggest that this adaptive phase may begin before insulin resistance is measurable, which makes the early period hard to separate from the later one.

Progressive beta-cell dysfunction

Compensation does not last. The loss of beta-cell function follows a recognisable sequence. First, the rapid early pulse of insulin that normally follows a glucose load is blunted, which mainly produces high glucose after meals. Next, the maximal secretory response to glucose and other nutrient signals declines. Finally, basal insulin secretion becomes inadequate, and insulin treatment is needed. Autopsy and imaging data show that beta-cell mass is reduced by roughly 40–60% in people with established type 2 diabetes. In a human islet amyloid polypeptide (IAPP) transgenic rat model, reduced beta-cell mass and impaired first-phase release appeared before impaired fasting glucose, and diabetes was accompanied by a deficit of around 70%. Increased apoptosis is a key contributor. In human pancreatic sections, islets containing more amyloid had less beta-cell area and more apoptotic beta cells, which suggests that amyloid deposits help drive cell loss. Whether the amyloid is a cause or a marker of beta-cell death remains under investigation.

From compensation to decompensation

The shift from compensated to decompensated hyperglycemia occurs when the beta cells can no longer match demand. Two toxic environments are thought to accelerate this decline. Glucotoxicity refers to the damage caused by chronically high glucose. Sustained hyperglycemia increases the production of reactive oxygen species in beta cells, impairs insulin secretion, and disrupts transcription factors such as PDX-1 and MafA that maintain the beta-cell identity and secretory machinery. Lipotoxicity refers to the damage caused by persistently elevated free fatty acids, which can accumulate as ceramides and other lipid intermediates that stress mitochondria and the endoplasmic reticulum. When both act together, the combined effect, called glucolipotoxicity, is greater than either alone, and it is associated with reduced insulin gene expression, impaired secretion and apoptosis. Endoplasmic reticulum stress, mitochondrial dysfunction and oxidative stress are the main intracellular routes to beta-cell death.

These processes are self-reinforcing. Higher glucose and lipid levels worsen beta-cell function, which raises glucose further and deepens insulin resistance. Because of this, interventions that lower glucose early and reduce lipid exposure may preserve beta-cell function better than treatments given later, a question addressed in the sections on prevention and pharmacological treatment.

Multi-Organ Hormonal Network and Chronic Inflammation

Incretin hormones and the gut

Glucose regulation depends on more than the pancreatic islets. After a meal, the gut releases incretin hormones, chiefly GLP-1 and GIP, which boost insulin secretion from beta cells. In people without diabetes, this gut-derived pathway supplies more than 50% of postprandial insulin secretion, which makes it a major limit on the post-meal glucose rise.

In type 2 diabetes, this amplification is markedly reduced or absent. The loss falls mainly on GIP. The incretin effect is reduced despite more or less normal secretion of GIP and GLP-1, and GIP has lost much of its acute insulin-releasing activity, while the insulin-stimulating action of GLP-1 is only slightly impaired. Early studies blamed weak GLP-1 secretion, but a later meta-analysis found no difference in incretin secretion between the two groups, so the defect appears to lie in the beta cell's response. Under hyperglycemia, GIP receptor expression on beta cells falls sharply, and the reduced incretin effect of GIP is recovered in those with type 2 diabetes once hyperglycemia has improved, which suggests the defect is partly reversible.

Glucagon, the kidney and the brain

Pancreatic alpha cells add a second hormonal disturbance. Type 2 diabetic patients are hyperglucagonaemic, and this seems to contribute to the development of hyperglycaemia. Chronic hyperglycemia itself appears to push alpha cells toward this pattern, because glucagon gene expression was higher in islets from T2D individuals and in normal islets exposed to chronic hyperglycemia. Excess glucagon drives hepatic glucose production, so the liver keeps releasing glucose even when intake is adequate.

The kidney adds a third contribution. SGLT2 reabsorbs ∼97% of filtered glucose in normoglycaemia, while SGLT1 reabsorbs ∼3%. Animal data suggest that diabetes raises this reabsorption by increasing the tubular glucose load and SGLT2 expression, which helps sustain hyperglycemia. Drugs that block SGLT2 therefore lower glucose through urine, but they also increase plasma glucagon concentrations and endogenous hepatic glucose production, a reminder that the hormonal and renal systems are tightly coupled. The brain, particularly the hypothalamus, integrates insulin, leptin and gut-derived signals to control appetite and energy expenditure, and disruption of this circuitry contributes to the obesity that often precedes diabetes.

Adipose tissue as an endocrine organ

Fat is not an inert energy store. Adipose tissue is the largest endocrine organ in humans, and it secretes adipokines that act locally and systemically. Adipose tissue from lean individuals preferentially secretes anti-inflammatory adipokines such as adiponectin, whereas obese adipose tissue mainly releases proinflammatory cytokines among which are TNF-α, IL-6, leptin, visfatin, resistin. These mediators act on insulin signaling directly or through inflammatory pathways. Pro-inflammatory cytokines such as IL-1β, IL-6 and TNFα create a pro-inflammatory environment that blocks adipocyte insulin action.

Immune cells amplify this shift. In lean tissue, macrophages adopt an anti-inflammatory state, but in obesity they are located around dead adipocytes and form so-called crown-like structures while displaying profound proinflammatory features. The resulting loop is self-reinforcing: macrophages engulf the lipid droplet causing further activation of macrophage inflammatory pathways, releasing their own inflammatory cytokines. Macrophage involvement appears to matter most after prolonged high-fat feeding, since the initial stage of insulin resistance is independent of macrophage action.

Chronic low-grade inflammation and vascular and renal disease

The inflammatory state is not confined to fat. In obesity, a state of chronic low-grade tissue inflammation is prevalent in adipose tissue and several other tissues including liver, skeletal muscle, pancreatic islets, and brain. Because this inflammation is systemic, it links adiposity to hyperglycemia and to vascular damage. Low-grade systemic inflammation and insulin resistance are implicated in the pathophysiology of type 2 diabetes mellitus, atherosclerosis, hypertension, and metabolic syndrome. The same inflammatory mediators that blunt insulin signaling are thought to promote endothelial dysfunction, plaque formation and glomerular injury, which helps explain why diabetes clusters with cardiovascular disease and kidney disease. The mechanistic links here are better established for the cardiovascular side than for the renal side, and the relative contribution of each pathway in individual patients remains uncertain.

Genetic Susceptibility

Type 2 diabetes is polygenic. No single gene determines who develops it. Risk arises from many common variants, each with a small effect, interacting with age, body weight and lifestyle. Twin research gives the clearest picture of the hereditary component. The DISCOTWIN consortium pooled data from about 34,000 same-sex twin pairs aged 45 and older in seven European registries and one Australian registry, and estimated heritability at about 72%. Other studies report lower figures. In a U.S. twin sample, heritability was about 52%, and early Danish and Finnish work produced estimates ranging from roughly 25% to 69%, depending on age and on how glycemia was defined. Family data point the same way: siblings of an affected person carry roughly 3.5 times the population risk. Identical twins are concordant more often than fraternal twins, yet discordance is common, so the environment plays a large role even in genetically identical pairs.

Loci and the beta-cell emphasis

Genome-wide association studies (GWAS) have expanded the known list of risk loci. A 2022 multi-ancestry meta-analysis led by Mahajan and colleagues, which included about 180,000 people with type 2 diabetes and more than one million controls, reported 237 loci reaching genome-wide significance. Most individual variants raise risk only modestly, typically by odds ratios below 1.2. A recurring pattern is that many of these loci affect the pancreatic beta cell rather than insulin action in peripheral tissues. Variants near genes such as HHEX, SLC30A8, CDKAL1 and IGF2BP2 were found to influence insulin secretion without clearly altering insulin sensitivity. Pathway clustering of established loci has likewise identified groups linked to reduced beta-cell function, separated by whether proinsulin levels are high or low. TCF7L2 remains the strongest and most consistently replicated signal, including in Indian cohorts. This emphasis on secretion matters for insulin biology, because it suggests that inherited limits on beta-cell capacity may set the stage for later insulin resistance to become clinically visible.

Ancestry and genetic architecture

Risk alleles and their effect sizes differ across populations. Lead variants identified in European and East Asian samples are largely concordant in effect size, whereas the correlation with African-ancestry effects is weaker. Polygenic risk scores built mainly from European data therefore perform less well in African, admixed American and South Asian populations. In one multi-ancestry validation, the odds ratio per standard deviation of the score was about 2.3 in European cohorts and 2.2 in East Asian cohorts, but about 1.4 in African or African American cohorts. Ancestry also shapes how genetic risk expresses itself clinically. East Asian individuals carry a higher share of lipodystrophy-like genetic risk, and T2D risk equivalent to that of a European at a BMI of 30 kg/m² appears at a BMI of about 24 in East Asian groups. Adjusting for these cluster-specific genetic effects explains most of that gap. Population-specific discoveries, such as a locus in sub-Saharan African cohorts linked to beta-cell apoptosis, further show that diverse study designs are needed to map the full genome.

Gene–environment interaction and epigenetic transmission

Genes rarely act in isolation. Obesity, diet and physical activity modify the expression of susceptibility variants, so a genetically predisposed person may remain normoglycemic in a lean, active setting but develop hyperglycemia after prolonged weight gain. Gene–environment interaction therefore helps explain why heritability estimates vary between populations and generations. Epigenetic mechanisms, including DNA methylation and histone modification in islets, liver, muscle and adipose tissue, can respond to nutrition and to the intrauterine environment, such as maternal hyperglycemia. These changes may contribute to familial clustering that is not fully captured by DNA sequence variation, and some animal and human studies suggest they can persist across generations. Evidence for stable transgenerational transmission in humans remains incomplete, and most familial aggregation is still attributed to inherited sequence variation combined with shared environments. Further detail on prenatal exposure is covered in the discussion of epidemiology and gestational diabetes.

Environmental and Lifestyle Risk Factors

Excess body weight is the dominant modifiable risk factor for type 2 diabetes. Risk rises in a nearly linear fashion as body mass index (BMI) increases across its whole range. Because overweight people far outnumber those with obesity, a great proportion of future cases comes from the population with a BMI between 25 and 30 kg/m², even though the highest risk is in obesity. Waist circumference adds information that BMI alone does not capture. BMI does not distinguish visceral fat from other fat, which is why waist measures are used to capture abdominal fat distribution. In the EPIC-Potsdam cohort, men or women of low or normal weight with a large waist had a 3.62-fold (men) or 2.74-fold (women) greater risk than persons of low or normal weight and small waist circumference. Among overweight adults, a large waist can place a person's ten-year risk close to that of people with obesity (waist circumference measurements identified a subgroup of overweight people whose 10-year cumulative incidence of type 2 diabetes was similar to that of obese people).

Dietary patterns act mainly through energy balance, fat distribution and insulin sensitivity. Sugar-sweetened drinks are among the most consistently implicated foods. In pooled analyses, each daily serving of sugar-sweetened beverage has been linked to roughly a 27% rise in type 2 diabetes risk, although estimates differ widely between studies. One dose-response analysis reported a much smaller per-unit association for artificially and sugar-sweetened beverages, and heterogeneity across studies was very high. The broader category of ultra-processed food has been studied intensively. Such foods are typically energy-dense; high in fat, sugar, and sodium; and low in fiber. In European cohorts, higher intake was linked to T2D risk being 15% to 53% higher depending on the cohort and the level of total UPF intake. The category is heterogeneous, however. Processed meats, ready-to-eat dishes and sugar- and artificially sweetened beverages are associated with increased risk, whereas yogurt and whole-grain breads and cereals are associated with reduced risk. Refined carbohydrates follow the same pattern: refined breads are linked to higher risk, while whole-grain products are linked to lower risk, which is consistent with the protective role of dietary fiber. Rapidly digested sugars and fats promote excess energy intake and weight gain, and they are thought to promote insulin resistance.

Physical inactivity works through many of the same pathways. Regular exercise appears to reduce risk even among people with high genetic susceptibility. One recent analysis found that meeting ≥150 minutes/week moderate-to-vigorous activity was associated with 39% lower risk, independent of genetic risk. Prolonged sedentary behaviour, which is common in desk-based work and screen-heavy leisure, is generally regarded as a separate risk factor, although its effect is harder to isolate from overall activity levels.

Sleep and work schedules also matter. A dose-response meta-analysis of prospective studies found a U-shaped relationship between sleep duration and risk of type 2 diabetes, with the lowest type 2 diabetes risk at 7–8 h per day. In a Korean cohort, adults who slept ≤5 h/night had a higher risk of incident diabetes than the reference group (HR, 1.17). Shift work shows a similar association. One meta-analysis found that night shift workers exhibited a 30% increased incidence of T2DM compared to their daytime counterparts, and risk appeared to rise with longer durations of night work. Another review reported a smaller pooled estimate and noted that female shift workers have increased risk of type 2 diabetes while male not observed. Such differences across meta-analyses reflect variation in study design, exposure definitions and adjustment for body weight.

Other exposures are supported by less consistent evidence and are generally considered additional rather than primary influences. Smoking is associated with a higher risk of type 2 diabetes and also worsens its vascular complications. Alcohol shows a more complex pattern, with heavy drinking increasing risk and moderate intake showing inconsistent associations across populations. Long-term exposure to air pollution, particularly fine particulate matter, has been associated with higher diabetes incidence, and the mechanisms may involve inflammation and insulin resistance. Early-life factors, including low birth weight, rapid infant weight gain and exposure to maternal diabetes in pregnancy, are thought to shape later susceptibility. Socioeconomic conditions shape nearly all of these exposures through food environments, occupational patterns, housing and access to health services, which is why they are often treated as social determinants of health rather than purely individual choices.

Global Epidemiology and Projected Burden

The most cited global count comes from the International Diabetes Federation's epidemiological Diabetes Atlas. Counting adults aged 20–79, the 2024 edition finds about 589 million people with diabetes, one in nine adults worldwide. The Atlas also reports that an estimated 252 million adults are living with undiagnosed diabetes, or 43% of adults living with diabetes. Almost 90% of the undiagnosed live in low and middle-income countries.

Projections are based on demographic change rather than on any assumed rise in risk. Based just on future trends in population growth, population aging, and urbanization, diabetes cases will increase 45% worldwide to 853 million by 2050. Age-standardised prevalence is expected to climb as well, to 12.96% by 2050. The largest relative increases fall on Africa and the Middle East and North Africa (MENA) region. Global mortality estimates differ by method. The Atlas reports more than 3.4 million people died as a result of diabetes in 2024, comprising 9.3% of global deaths. By contrast, the Global Burden of Disease (GBD) 2021 analysis counted 1.66 million deaths from diabetes in 2021, and Type 2 diabetes accounted for 97.1% of deaths.

The GBD study provides a complementary, type-specific view. It covers type 1 and type 2 diabetes across all ages, for 204 countries and territories. It reports 529 million people living with diabetes worldwide in 2021, and a global age-standardised total diabetes prevalence of 6.1%. Its projections are higher still, with more than 1·31 billion (1·22–1·39) people expected to have diabetes by 2050. These figures are not directly comparable with the Atlas because of differences in age range, case definitions and modelling, and the GBD study also quantifies the proportion of type 2 diabetes attributable to 16 selected risk factors.

Burden is unevenly distributed. The Atlas places the highest age-standardised diabetes prevalence in the MENA region, at 19.91% in 2024, while the Africa region had the lowest age-standardised diabetes prevalence at 5·04%. The low African figure partly reflects data gaps, since about half (45%) of the countries in the IDF AFR Region lack high-quality, in-country data sources. The Western Pacific holds the largest absolute number, with 215 million adults living with diabetes. Within the Pacific, GBD data show Pacific Island nations exhibited incidence rates >800/100,000, contrasting with <3/100,000 in Costa Rica and China. South Asia is also heavily affected, with almost half of the adults living with diabetes in the region undiagnosed. Income is a further axis of inequality: 4 in 5 adults with diabetes (81%) live in low and middle-income countries. The fastest growth is expected in poorer settings, where the highest relative increase in the number of people with diabetes was projected to occur in LICs (135·07%) in 2050.

Several forces are expected to shape future trends. Urbanisation matters because diabetes prevalence is associated with urban living, a link the Atlas stratifies by urban–rural location. Population ageing also drives the count, since one in four adults living with diabetes is >65. The pool of future cases is already large: 635 million adults worldwide (1 in 8) have impaired glucose tolerance and 488 million have impaired fasting glucose (1 in 11) placing them at high risk of type 2 diabetes. Whether that pool converts into diagnosed disease depends on the public health responses discussed later, as well as on rising obesity and dietary and activity patterns.

Clinical Presentation and Acute Complications

Symptoms and silent onset

Hyperglycemia in type 2 diabetes usually develops over years. Its typical features are excessive urination, thirst, weight loss and fatigue, but these tend to be mild and nonspecific. Many people have no complaints at diagnosis. The condition is often found on a routine blood test, or only after a microvascular or cardiovascular complication has appeared. Residual insulin secretion keeps glucose within a tolerable range for a long time, which masks the problem.

Hyperosmolar hyperglycemic state

Extreme hyperglycemia, raised serum osmolality and dehydration define the hyperosmolar hyperglycemic state (HHS), while ketones are scarce or absent. Current diagnostic HHS criteria include a plasma glucose level above 600 mg/dL and an increased effective plasma osmolality above 320 mOsm/kg in the absence of ketoacidosis. The process generally unfolds over several days, sometimes weeks. Clinicians typically find low blood pressure, a rapid pulse and poor skin turgor on examination, and altered sensorium, ranging from lethargy to disorientation and stupor, is common and correlates best with effective serum osmolality. Seizures can occur in up to 20% of patients.

HHS is rare but dangerous. It accounts for less than 1% of hospital admissions of patients with diabetes, yet its fatality rate is much higher than that of ketoacidosis. The overall mortality rate is estimated to be as high as 20%, which is about 10 times higher than the mortality in patients with diabetic ketoacidosis. Death rates are higher at the extremes of age and when coma is present on admission. In a Danish cohort, the in-hospital mortality rate for pure HHS was 17% and 9% for HHS-DKA. In a Japanese hospital series, infections (51.2%) were the most common trigger, and the isolated HHS group had a significantly higher 30-day mortality rate (26.0%). Most patients in that series were not taking any glucose-lowering drug. Treatment centers on correction of fluid deficit and electrolyte abnormalities, and intravenous insulin. Correction must be gradual, because it is important to monitor these patients closely to avoid overcorrection of osmolality, sodium, and other electrolytes.

Ketoacidosis in type 2 diabetes

Diabetic ketoacidosis (DKA) is classically linked to profound insulin deficiency, as in type 1 diabetes. Its occurrence in type 2 diabetes was therefore unexpected, and initial case reports often described patients with blood glucose below 200 mg/dL, a pattern called euglycemic DKA. The main type 2 pathway runs through SGLT2 inhibitors. The mechanism is mainly enhanced lipolysis and ketone body reabsorption. The drugs also stimulate pancreatic alpha cells and inhibit beta cells, causing an imbalance in glucagon/insulin levels.

Risk is not trivial. One nationwide cohort estimated that Diabetic ketoacidosis affected approximately 2 per 1000 patients starting to use an SGLT2 inhibitor. A 2026 Nordic cohort recorded 1,452 ketoacidosis events during a median follow-up of 1.3 years (incidence, 2.43 per 1,000 person-years), with risk highest soon after initiation and persisting through follow-up. Strong risk factors in that study included high hemoglobin A1c, malnutrition, previous ketoacidosis, low body mass index, and recent hypoglycemia. The most common precipitating or co-occurring event was infection. Other triggers include inappropriate dose reductions of insulin, the dietary restriction of carbohydrates, and factors that may increase insulin demand such as excessive alcohol intake and major surgery. Patients with blood glucose less than 200 mg/dL, blood pH below 7.3, increased anion gap, or increased blood or urine ketones may be missed if clinicians rely on glucose alone.

Hypoglycemia

Hypoglycemia is the main hazard of insulin and sulfonylureas, which can push glucose down regardless of meal intake. Treatment is usually started below 70 mg/dL, a threshold the American Diabetes Association uses when deciding whether to apply the rule of 15. Early warning signs include sweating, tachycardia, tremor, palpitations, nervousness, hunger, pallor, confusion, lethargy, uncharacteristic behavior, irritability, seizures, and coma. Risk rises with recent episodes, insulin, impaired awareness of hypoglycemia, fear of hypoglycemia, kidney disease, dementia, and alcohol consumption.

For mild episodes, the standard approach is the 15-15 rule: have 15 grams of fast-acting carbohydrates, and recheck glucose in 15 minutes. If the level is still low, they have another 15 g of carbs and wait another 15 minutes to check again. Research has questioned whether the rule always works as intended. Canadian researchers have found that on average, treating one hypoglycemic episode takes more than 15 minutes and often requires more than 15 g of carbohydrates. For dangerous lows, the most effective treatment for dangerously low blood sugar is injectable glucagon.

Recurrent hypoglycemia calls for a change in treatment. Guidance recommends that treatment plans be reevaluated after level 2 or 3 hypoglycemia, with consideration of less intense therapy or different medications. Continuous glucose monitoring is recommended for people using insulin, or with a history of or high risk for hypoglycemia.

Chronic Complications and Their Mechanisms

Microvascular complications

Sustained hyperglycemia injures small blood vessels and nerves, producing the three classic microvascular complications: diabetic retinopathy, diabetic kidney disease and diabetic peripheral neuropathy. Retinopathy is a leading cause of vision loss in working-age and older adults. DR stands out as one of the most common microvascular complications and a leading cause of vision impairment in both working-age and older adults. In the retina, the thickening of capillary basement membranes and rising vascular permeability lead to tissue ischemia and, eventually, the growth of abnormal new vessels. Microvascular dysfunction induces ischemia and local inflammation, leading to neovascularization, macular edema, and neurodysfunction. Laser treatment has proven effective: landmark clinical trials during the 1980s demonstrated that laser photocoagulation can effectively prevent the loss of vision in the patients with proliferative DR or diabetic macular edema. Neuropathy is equally common; diabetic neuropathy is one of the most common and severe manifestations of diabetes mellitus. Even with careful glycemic control, complications, including retinopathy, nephropathy, vascular and cardiac conditions, and neuropathy, still affect many patients with diabetes.

Metabolic pathways and oxidative stress

Researchers have traced much of this tissue damage to four glucose-driven pathways: increased flux of the polyol pathway; PKC activation; increased intracellular production of AGEs; and overactivation of the hexosamine pathway. In the polyol pathway, excess intracellular glucose is channelled into sorbitol by aldose reductase (AR), the rate-limiting enzyme in the pathway, which reduces unused glucose to sorbitol. This process consumes NADPH, and decreased levels of NADPH are responsible for the ROS accumulation and oxidative stress damage. A parallel route generates reactive dicarbonyls: methylglyoxal, a precursor of diacylglycerol (DAG) and AGEs, thereby leading to the activation of the AGE and PKC pathways. Non-enzymatic glycation of proteins produces advanced glycation end-products, which accumulate in vessel walls and extracellular matrix.

Reactive oxygen species are the common output of these routes. The hyperglycemia-induced overproduction of reactive oxygen species (ROS) induces local inflammation, mitochondrial dysfunction, microvascular dysfunction, and cell apoptosis. Early research treated each pathway separately, and while specific inhibitors of each pathway block one or more diabetic microvascular complications, only recently has a link been established that provides a unified mechanism of tissue damage. One proposed unifying route involves DNA damage: oxidative stress mediated DNA damage causes poly(ADP-ribose) polymerase (PARP) overactivation and reduced activity of glyceraldehyde 3-phosphate dehydrogenase (GAPDH), a factor common to all the four pathways. The retina is especially vulnerable, because of high energy demands and exposure to light.

Macrovascular complications

Large-vessel disease is driven mainly by atherosclerosis. Macrovascular (cardiovascular) disease encompasses myocardial infarction, stroke and peripheral arterial disease. It is caused by atherosclerosis, a complex pathological process that is accelerated in people with diabetes. Among people with type 2 diabetes, this vascular burden is the main driver of excess death: while hyperglycemia is a hallmark of T2DM, the primary contributor to increased mortality risk in these patients is macrovascular complications induced by atherosclerosis. Stroke risk is substantially raised; a meta-analysis of 102 prospective studies reported an adjusted hazard ratio of 2.27 (95% CI, 1.95–2.65) for ischemic stroke among those with type 2 diabetes compared to those without. Peripheral arterial disease is common in this group, with prevalence estimates ranging from 15.2% to 40%, and it carries serious consequences, since in type 2 diabetes it increases the risk of lower extremity amputation up to 5 times higher.

Cognitive, infectious and skeletal consequences

Long-standing hyperglycemia also affects organs beyond the vasculature. Cognitive decline is a notable example; one review notes that it occurs in more than half of the patients with type 2 diabetes (T2DM), although estimates vary across studies. In a cross-sectional analysis, hyperglycemia and the duration of diabetes are the major factors contributing to cognitive decline in patients with T2D. Proposed mechanisms include inflammation that weakens the blood–brain barrier, with mouse models pointing to a strong association between hyperglycaemia, the advanced glycation end products glyoxal and methylglyoxal, enhanced blood–brain barrier (BBB) permeability and cognitive dysfunction.

Infection risk is raised as well. Hyperglycemia may impair neutrophil function, as hyperglycaemic states might give rise to reductions in the mobilization of polymorphonuclear leukocytes, phagocytic activity and chemotaxis, and people with diabetes have higher rates of hospitalization and mortality from various infections, including COVID-19, pneumonia, foot and kidney infections. Bone is also affected: type 2 diabetes increases the risk of fracture risk and secondary hypogonadism. After hip fracture, patients with type 2 diabetes face a higher risk of death, presumably due to the increased risk of post-operative complications like postoperative pneumonia, deep surgical site infections, and postoperative delirium.

Prevention and Prediabetes

Prediabetes refers to glucose levels above normal that remain below the diagnostic threshold for diabetes, whether through impaired fasting glucose, impaired glucose tolerance, or an HbA1c of 5.7% to 6.4%. Because a large share of these individuals go on to develop diabetes, it has been the main target of randomized controlled trials testing whether progression can be slowed or prevented.

The best-known of these is the US Diabetes Prevention Program (DPP), which enrolled 3,234 adults with prediabetes and assigned them to intensive lifestyle intervention, metformin, or placebo. After a mean follow-up of 2.8 years, the lifestyle arm had 58% fewer cases of diabetes than placebo and the metformin arm had 31% fewer. Both effects were large enough that the trial was stopped ahead of schedule. Much of metformin's benefit appeared to follow from the modest weight loss it produced, with roughly two-thirds of its effect attributed to that loss. The lifestyle program, by contrast, combined dietary change with physical activity and aimed at about 7% body-weight reduction.

Early benefits have proved durable in several cohorts, although the size of the effect shrinks over time. The Finnish Diabetes Prevention Study, which ran a lifestyle intervention for a median of four years, reported a 38% relative risk reduction after a median of nine years of follow-up. The China Da Qing study, which used a six-year group-based intervention in people with impaired glucose tolerance, found roughly 43% lower diabetes incidence up to 14 years after the active phase ended, with onset delayed by an average of 3.6 years. The DPP's 21-year follow-up reported diabetes reductions of 24% for lifestyle and 17% for metformin, extending the median time free of diabetes by 3.5 and 2.5 years respectively. Benefits for cardiovascular outcomes are less clear. In the DPP Outcomes Study, neither intervention reduced major cardiovascular events over 21 years, a result the authors partly attributed to group lifestyle support being offered to all participants and to extensive use of statins and antihypertensive drugs outside the study. Da Qing investigators, by contrast, have reported lower rates of retinopathy, cardiovascular death and all-cause mortality in their combined lifestyle group at longer follow-up.

Screening is the first step in identifying people for these interventions. Current American Diabetes Association (ADA) guidance recommends that asymptomatic adults be assessed for risk using a validated calculator or an informal review of risk factors. Testing should be considered at any age in adults with overweight or obesity (BMI ≥25 kg/m², or ≥23 kg/m² in people of Asian ancestry) who also have a first-degree relative with diabetes, high-risk ethnic background, prior cardiovascular disease, hypertension, or an unfavourable lipid profile. Other adults should begin screening at age 35. Normal results are typically repeated at least every three years, while people with prediabetes are tested yearly and people with a history of gestational diabetes every one to three years. The ADA also advises considering screening for people taking certain drugs, such as statins, thiazide diuretics and some HIV medications, that raise diabetes risk. The United States Preventive Services Task Force (USPSTF) takes a narrower approach, recommending screening for adults aged 35 to 70 with overweight or obesity. In a 2010 modelling study using US survey data, the ADA criteria would have identified about 39% more cases of prediabetes and 24% more cases of type 2 diabetes than the USPSTF criteria. The trade-off is specificity: a study of the ADA's 2023 criteria found high sensitivity (about 95%) but low specificity (about 27%), meaning many people flagged would not have dysglycaemia.

Early intervention is directed at people judged to be at high risk, including those with a history of gestational diabetes, a family history of type 2 diabetes, or several metabolic risk factors. The Finnish national prevention programme, a primary-care-based scheme, illustrates how such programmes can be delivered outside trials. Its one-year intervention was associated with a 69% reduction in risk among participants who lost 5% of their body weight. Because risk-based targeting depends on the availability of testing and follow-up, the composition of high-risk groups and their access to services have consequences for how benefits are distributed across populations.

The economic case for prevention rests partly on cost-effectiveness analyses of the DPP. Over a ten-year horizon, both lifestyle change and metformin were more expensive than placebo, but the additional costs were offset by lower spending on other medical care, and both interventions were judged highly cost-effective or cost-saving. Participants in the lifestyle arm also reported better quality of life each year after randomization. The main obstacle is sustaining change. In the DPP Outcomes Study, the lifestyle group regained about 3.5 kg of its initial loss, while the metformin group kept more of its weight loss, around 6.2% compared with 3.7% in the lifestyle group, between years 6 and 15. Older age and the amount of weight lost early in the programme were the most consistent predictors of long-term weight maintenance. These findings suggest that population-level prevention depends on durable support, not on a single intensive phase, and that its benefits are shaped by health-system organization, screening coverage and social conditions.

Glycemic Targets and Monitoring

Individualized glycemic targets

Glycemic goals are set for each person rather than applied uniformly. The 2026 American Diabetes Association standards give a general target for most nonpregnant adults of an HbA1c below 7%, with time in range above 70%, time below range under 4%. Looser or tighter goals are then adjusted around that anchor. Lower HbA1c goals, such as below 6.5%, may be appropriate for individuals with good health and function and low treatment risks, such as hypoglycemia, and burdens. At the other end of the spectrum, older adults with multiple chronic illnesses or impaired cognition or function are usually given less stringent targets. For them, the standards describe an HbA1c below 8% and a time in range of at least 50%, and they stress that selection of glycemic goals should prioritize avoidance of hypoglycemia.

Clinicians weigh comorbidity, functional status, cognitive capacity, hypoglycemia risk and life expectancy, rather than chronological age alone. Glycemic targets should be individualized based on comorbidities, functional status, cognitive function, hypoglycemia risk, and life expectancy rather than chronological age alone. Goals also need to be revisited over time. When a person is at high risk of hypoglycemia, clinicians may reduce or replace agents such as insulin, sulfonylureas or meglitinides, which are the drugs most likely to cause low glucose, and switch to a medication class with lower hypoglycemia risk. This is discussed further under treatment.

Self-monitoring of blood glucose and continuous glucose monitoring

Self-monitoring of blood glucose uses fingerstick measurements taken at chosen times of day. It is useful for checking the effects of meals, exercise and medication changes, but it captures only isolated moments. Continuous glucose monitoring (CGM) addresses this limitation. A subcutaneous sensor measures interstitial glucose levels nearly continuously allowing insights into short and medium-term fluctuations in glucose levels, and it reports readings at intervals of minutes rather than hours.

CGM data are summarized with standardized metrics. The 2019 international consensus on time in range (TIR) set the core range at 70–180 mg/dL for most people with type 1 or type 2 diabetes. It recommended a TIR above 70%, time below 70 mg/dL under 4%, and time below 54 mg/dL under 1%. TIR is strongly correlated with HbA1c, and it has been linked to the risk of developing microvascular and macrovascular complications. Other core metrics include time above range, the glucose management indicator (an estimate of HbA1c derived from CGM data), glycemic variability and mean glucose. Reliable interpretation generally requires at least 14 days of data with active wear for roughly 70% of that period. Some investigators have proposed a tighter band of 70–140 mg/dL, which they call time in tight range (TITR), for people aiming at near-normal glucose levels. TITR was identified and recommended recently as an important additional CGM-derived glucose metric covering glucose ranges of 70–140 mg/dL.

Evidence for CGM in type 2 diabetes is growing but uneven. A large real-world analysis of CGM users found that the T2D groups, regardless of treatment type, displayed the highest TIR and TITR values, but the authors noted that there are still limited reports of large data sets from real-life settings, and particularly lacking are data in noninsulin-treated type 2 diabetes. The 2026 standards have moved toward earlier access. Technology, including CGM and AID, is now recommended soon after diagnosis in both type 1 and type 2 diabetes, with fewer restrictions.

The role of HbA1c in routine monitoring

HbA1c remains the main routine laboratory measure because it is standardized, widely available and linked to outcomes. Its limitations are well recognized. It reflects average glycemia over roughly three months and does not reveal daily swings or nocturnal lows. Many patients also have a poor understanding of what the number means. Most people with T2D have suboptimal recall and understanding of HbA1c. Physicians therefore often pair HbA1c with other measures. TIR is now firmly established alongside HbA1c as a primary clinical target.

Additional measures are most useful in particular situations: people treated with insulin, those with frequent hypoglycemia, pregnant women, older or frail adults, and patients facing surgery. In the perioperative setting, the 2026 standards suggest an HbA1c below 8% within three months of elective surgery, and the 14-day glucose management indicator goal <8% and/or time in range >50% can also be used.

Patient education, self-management and digital tools

Monitoring data only help when people can interpret and act on them. Structured diabetes self-management education covers meal planning, medication timing, sick-day rules, and how to recognize and treat low and high glucose. Clinicians also agree on individual goals with patients, which supports adherence. Digital tools, including glucose meter apps, connected sensors, and remote data sharing with care teams, can make review of trends easier and allow earlier adjustment of therapy. Automated insulin delivery is one example. AID systems are the preferred insulin delivery system for people with type 1 diabetes and adults and children with type 2 diabetes on multiple daily injections, CSII, or sensor-augmented pump therapy.

Access to these tools is uneven. Devices, smartphones, data plans and the skills to use them are unevenly distributed, and this can widen the digital divide and existing income inequality in diabetes care. Programs that combine digital monitoring with human support, and that consider cost and digital literacy, are therefore more likely to benefit people across all socioeconomic groups.

Lifestyle Treatment and Weight Management

Medical nutrition therapy

Medical nutrition therapy (MNT) is treated as the foundation of diabetes management, and its details are adjusted whenever medication or activity changes. Consensus reports reject one-size-fits-all meal plans as unsupported, stress individualization, and call for MNT to be revised when drugs or activity levels change. In practice, weight-reduction plans usually aim for a daily energy deficit of roughly 500–750 kcal, which in many adults means intakes of about 1,200–1,500 kcal per day for women and 1,500–1,800 kcal per day for men (though the same source notes that weight loss guidance is far better established than the nutritional plan itself).

Evidence on macronutrients remains contested. Within hypocaloric plans, no single optimal macronutrient distribution has been identified, so recommendations are best tailored to personal preference to support long-term adherence. Low- and very-low-carbohydrate patterns have improved glucose control and weight in trials, but their long-term sustainability is debated, and concerns exist that compensatory increases in saturated fat could raise cardiovascular risk (low-carbohydrate patterns of ≤10% and 10–26% of energy have proven effective in trials, though whether they can be sustained long term is arguable and a compensatory rise in fat intake has been voiced as a concern). Mediterranean-style, plant-based and other eating patterns with calorie deficits have all shown benefits. Common advice is to favour non-starchy vegetables, legumes, whole grains and low-fat dairy while limiting refined carbohydrates, added sugars and processed foods, and to meet a fibre target of at least 14 g per 1,000 kcal, which is consistent with general-population guidance.

Physical activity and insulin sensitivity

Current American Diabetes Association guidance advises most adults with type 2 diabetes to accumulate at least 150 minutes of moderate-to-vigorous aerobic activity a week, spread over several days, with shorter vigorous or interval sessions acceptable for fitter individuals. It also recommends resistance exercise on two or three non-consecutive days each week, and breaking up prolonged sitting at least every 30 minutes because of its effect on blood glucose. Aerobic training improves muscle insulin sensitivity, and resistance training has been linked to better glycemic control and reduced fat mass in type 2 diabetes. A dose-response meta-analysis of randomized trials suggested an optimal volume of about 1,100 MET-minutes per week, with the benefit on HbA1c evident across glycemic categories. Systematic reviews have nevertheless noted that strength and flexibility work receives less emphasis in guidelines than aerobic exercise, and that activity plans need adjustment for insulin dosing and hypoglycemia risk, a topic covered in the discussion of hypoglycemia.

Intensive weight loss and diabetes remission

The clearest evidence for lifestyle treatment comes from weight loss trials. The ADA suggests that adults with overweight or obesity aim for weight reduction of at least 5%. For people with short-duration disease, remission will usually require 10–15% body weight loss. The Diabetes Remission Clinical Trial (DiRECT), a cluster-randomized trial in UK primary care, tested a low-energy total diet replacement phase of 825–853 kcal per day for 3–5 months, followed by stepped food reintroduction and maintenance support. At 12 months, diabetes remission was achieved in 68 (46%) participants in the intervention group and six (4%) participants in the control group. Only 24% of the intervention group had lost 15 kg or more, and mean weight fell by 10 kg, compared with 1 kg in controls. Remission in DiRECT was defined as an HbA1c below 6.5% after at least two months off all antidiabetic drugs. At two years, 68 (46%) of 149 intervention participants were in remission and 36 (24%) had achieved at least 15 kg weight loss at 1 year, and durability was assessed by the follow-up analysis, which found that sustained remission was linked to the extent of sustained weight loss. In the five-year extension, participants who kept more than 10 kg of weight loss at two years showed high remission rates, with 29 (81%) in remission among those 36 people.

Replications have produced similar results. The DiRECT-Aus study in Australian primary care recorded T2D remission in 86 (56%) participants at 12 months, with a mean adjusted weight loss of 8.1%. The DIADEM-I trial in the Middle East and North Africa has also reproduced the pattern, which has led some authors to argue for prioritizing remission programmes soon after diagnosis. Remission should not be equated with cure, however: the relapse risk is substantial when weight is regained, and the programmes depend on intensive dietitian and behavioural support that is difficult to deliver in routine care.

Behavioural and psychological support

Structured behavioural support is considered essential alongside diet and activity. Guidance states that weight-loss interventions should be combined with diabetes self-management education, nutrition therapy, and physical activity to improve glycaemic control, cardiovascular risk factors, and quality of life. The main obstacle is sustaining change. A qualitative study nested within a pilot trial in a Māori primary care setting in New Zealand found that family and social networks encouraged participants, while eating-related cultural norms made adherence harder, and it concluded that individualized, culturally relevant support is needed. More broadly, sustaining weight loss remains a challenge, but any amount of weight loss has been associated with benefit, so programmes often emphasize incremental goals rather than all-or-nothing targets. Digital tools are being explored as a lower-cost way to extend structured support, although access gaps may limit their reach.

Pharmacological Treatment I: Oral Agents and Insulin

Metformin

Metformin, a biguanide, is the usual first drug, and guidelines place it at the start of the treatment sequence. Its profile is attractive because it lowers A1C without adding weight, rarely causes low blood glucose on its own, and has been linked to fewer cardiovascular deaths. The ADA's Standards of Care in Diabetes describes metformin as effective and safe, stating that "as first-line therapy [it] has beneficial effects on A1C, is weight neutral, does not cause hypoglycemia, and reduces cardiovascular mortality."

Most of its effect comes from the liver. In individuals with type 2 diabetes, metformin reduced hepatic glucose output by up to 75%, primarily through suppression of gluconeogenesis. The classic explanation holds that metformin inhibits mitochondrial complex I, which lowers hepatocyte energy charge and activates AMP-activated protein kinase (AMPK). This model is contested, because metformin still suppresses hepatic glucose production in mice lacking AMPK. Other proposed actions include reduced intestinal glucose absorption and, more recently, increased glucose uptake by the gut. In hyperglycemic conditions, metformin increases basolateral intestinal glucose uptake, and its metabolites produced in the gut reach the liver through the portal vein and reduce hepatic glucose production. The most common adverse effects are gastrointestinal, including diarrhea, nausea and abdominal discomfort, which are usually dose-related and often improved by extended-release formulations. Long-term use is associated with vitamin B12 deficiency, and lactic acidosis is rare but serious, which is why dosing is limited in advanced kidney impairment.

Sulfonylureas and Meglitinides

Sulfonylureas (such as glibenclamide, glimepiride, gliclazide and glipizide) close ATP-sensitive potassium channels in pancreatic beta cells, which increases insulin secretion regardless of the prevailing glucose level. This mechanism is effective and inexpensive, but it carries a substantial risk of hypoglycemia and tends to cause weight gain. Meglitinides (repaglinide and nateglinide) act through the same channels but are short-acting and taken before meals. They control postprandial glucose more flexibly, though they require frequent dosing and still provoke hypoglycemia.

Thiazolidinediones

Pioglitazone and rosiglitazone are agonists of PPAR-gamma, a nuclear receptor that improves insulin sensitivity in adipose tissue, muscle and liver. Their glucose-lowering effect is durable, but they cause weight gain and fluid retention, can precipitate or worsen heart failure, and increase fracture risk. Pioglitazone has attracted interest for fatty liver disease. Pioglitazone or a dual GIP and GLP-1 RA can be considered for glycemic management in adults with biopsy-proven MASH or high risk of liver fibrosis.

DPP-4 Inhibitors

Sitagliptin, linagliptin, saxagliptin and alogliptin block dipeptidyl peptidase-4, the enzyme that degrades incretin hormones, thereby prolonging GLP-1 and GIP action and enhancing glucose-dependent insulin secretion. They are weight-neutral and carry a low risk of hypoglycemia, but their A1C-lowering effect is modest and they have not shown cardiovascular benefit. Saxagliptin was associated with a signal of heart failure hospitalization in a cardiovascular outcome trial. In the ADA's Standards of Care in Diabetes—2026, a recommendation advises against using a DPP-4 inhibitor concurrently with a GLP-1 receptor agonist or a dual GIP/GLP-1 receptor agonist, due to lack of additional glucose lowering beyond that of GLP-1–based therapy.

Alpha-Glucosidase Inhibitors

Acarbose and miglitol slow the intestinal breakdown of starch and sucrose, which blunts postprandial glucose excursions. They lower A1C only modestly and are taken with the first bites of a meal. Flatulence, bloating and diarrhea limit their use, and they are used mainly in selected patients with prominent post-meal hyperglycemia.

Insulin Therapy

Insulin types fall into several groups. Long-acting basal analogues (glargine, detemir and degludec) provide a steady background level, and intermediate-acting NPH is a cheaper alternative. Rapid-acting prandial analogues (lispro, aspart and glulisine) cover meal-related glucose rises, and regular human insulin is used less often. Premixed preparations combine basal and prandial components in fixed ratios.

Regimens range from once-daily basal insulin added to oral agents, through basal-bolus regimens with meal-time doses, to twice-daily premixed insulin. Basal insulin is typically started at a low dose and titrated against fasting glucose. Clinicians avoid hypoglycemia by reducing doses when fasting values fall too low, by adjusting prandial doses to carbohydrate intake and activity, and by lowering or stopping sulfonylureas once insulin is introduced. Combining insulin with a GLP-1 receptor agonist is preferred because it achieves greater glucose lowering with less hypoglycemia and less weight gain than insulin alone.

Sequencing and Combination

Treatment is stepwise and individualized. Lifestyle measures and metformin usually come first, and a second agent is added when the A1C target is not met. The choice of additional drugs depends on weight, hypoglycemia risk, cost, tolerability and comorbidity. Because type 2 diabetes is a progressive disease, maintenance of glycemic control requires ongoing reassessment. As beta-cell function declines, two- and three-drug oral combinations often fail, and insulin becomes necessary. Current guidance increasingly favors GLP-1 receptor agonists and SGLT2 inhibitors for patients with cardiovascular, kidney or heart disease, irrespective of A1C, a shift discussed in the following section.

Pharmacological Treatment II: GLP-1, SGLT2 and Organ Protection

GLP-1 receptor agonists and dual GIP/GLP-1 agonists

GLP-1 receptor agonists are synthetic drugs that act on the receptor for the gut hormone GLP-1, which is released after meals. Because they stimulate insulin secretion only when glucose is elevated, they lower glycaemia with a comparatively low intrinsic risk of hypoglycaemia. They also suppress glucagon, slow gastric emptying and increase satiety, which is why they lower body weight as well as blood glucose. GLP-1 receptor agonists mimic these actions and have demonstrated robust efficacy in both glycemic control and weight outcomes.

Tirzepatide acts on both the GIP and GLP-1 receptors. The US Food and Drug Administration approved it on May 13, 2022, to improve blood sugar control in adults with type 2 diabetes as an adjunct to diet and exercise. It can lower hemoglobin A1c more than other medications to which it was compared. In trials in adults with obesity but without diabetes, the placebo-corrected weight loss was around 5 % for liraglutide, 12 % for semaglutide and 18 % for tirzepatide. A 2026 network meta-analysis of 15 randomised trials found that the largest reduction occurred with the maximum tolerated dose of tirzepatide.

Gastrointestinal effects are the main barrier to sustained use. Common adverse events include nausea, vomiting, diarrhoea and constipation, with a significantly higher incidence of nausea than with placebo. Weight regain after stopping treatment and long-term metabolic outcomes remain under-studied, and reviewers have called for more research on discontinuation and weight regain.

SGLT2 inhibitors

SGLT2 inhibitors block glucose reabsorption in the proximal renal tubule, which produces glycosuria, osmotic diuresis and natriuresis. These changes not only lower blood glucose but also reduce fluid overload and improve cardiac hemodynamics, providing cardiovascular and renal benefits independent of glycemic control. The cardiorenal benefits are therefore largely independent of how much glucose they lower.

In heart failure, the evidence is substantial. A meta-analysis of six large trials, enrolling more than 47,000 people with type 2 diabetes, found that SGLT2 inhibitors were associated with a 28% relative risk reduction in heart failure hospitalisation compared with placebo or standard care. For kidney outcomes, a pooled analysis of placebo-controlled trials reported that allocation to an SGLT2 inhibitor reduced the risk of kidney disease progression by 37%. Guidelines now recommend these drugs for adults with type 2 diabetes and chronic kidney disease when the eGFR is at least 20 mL/min/1.73 m², and the DECLARE-TIMI 58 trial suggested benefit even in people with normal urinary albumin levels.

Guideline positions and sequencing

The 2026 ADA Standards of Care, published December 8, 2025, recommend that adults with type 2 diabetes and established or high-risk atherosclerotic disease receive a GLP-1 receptor agonist and/or an SGLT2 inhibitor with proven cardiovascular benefit, irrespective of A1C. For heart failure, an SGLT2 inhibitor is recommended both for glycaemic management and for preventing hospitalisation. In advanced chronic kidney disease (eGFR below 30), a GLP-1 receptor agonist is preferred partly because of lower risk of hypoglycemia and for cardiovascular event reduction. The 2026 guideline also allows simultaneous initiation of an SGLT2 inhibitor and the non-steroidal mineralocorticoid receptor antagonist finerenone in selected patients with albuminuric CKD.

The 2026 ADA-EASD consensus goes further in terms of timing. It suggests that SGLT2 inhibitors and GLP-1-based therapies should be considered early, potentially from diagnosis, because of their cardiovascular, kidney and metabolic benefits independent of metformin. It also positions SGLT2 inhibitors as the foundation of heart failure and kidney protection, with GLP-1-based drugs adding further benefit. Some experts have framed this as a shift in philosophy. One commentator acknowledged that one might quibble about whether a GLP-1 receptor agonist or an SGLT-2 inhibitor is the ideal drug or not, but what we're suggesting is that you should at least consider it. Metformin, sulfonylureas and other older agents remain relevant for glucose lowering, but they do not carry comparable outcome data for organ protection, which is why they are increasingly placed after these newer classes in treatment algorithms.

Cost, access and tolerability

Real-world prescribing depends on several factors beyond efficacy. Brand-name GLP-1 drugs are expensive, and coverage differs widely between health systems and insurers; prior authorisation requirements can delay or prevent initiation, which may widen existing inequalities among socioeconomically disadvantaged groups. Periods of supply shortage and the spread of unregulated compounded products have raised additional safety and access concerns.

Each class has tolerability issues. SGLT2 inhibitors are associated with genital mycotic infections, volume depletion and, rarely, euglycaemic ketoacidosis, which requires attention to sick-day rules. GLP-1-based drugs carry warnings from regulators on pancreatitis, gallbladder disease and, for some products, thyroid C-cell tumours seen in rodent studies. Long-term safety data beyond the initial trial periods, and the cost-effectiveness of these agents across populations, are areas where evidence is still developing.

Cardiovascular and Kidney Risk Management

Most people with type 2 diabetes die of cardiovascular rather than glycemic causes, so management aims at blood pressure, lipids, kidney protection and antithrombotic therapy alongside glucose control. Current recommendations in this area are more specific than they were a decade ago, and they overlap with the drug classes described in the pharmacological sections.

Blood Pressure

The 2026 American Diabetes Association (ADA) Standards of Care set an on-treatment goal of <130/80 mmHg for most adults with diabetes, <FONT>provided it can be reached safely</FONT>. If it can be safely attained, the on-treatment blood pressure goal is <130/80 mmHg; a systolic blood pressure goal <120 mmHg should be encouraged in individuals with high cardiovascular or kidney risk. The stricter systolic target rests on the BPROAD and ESPRIT trials, the first of which randomized people with diabetes and elevated cardiovascular risk to intensive systolic lowering. For older adults, a more relaxed goal of <140/90 mmHg is acceptable when health is poor or life expectancy is limited. The on-treatment blood pressure goal for most older adults with diabetes is <130/80 mmHg when it can be achieved safely, and more a relaxed blood pressure goal (e.g., <140/90 mmHg) may be used for people with poor health, limited life expectancy, or high risk for adverse effects of hypertensive therapy.

When albuminuria is present, drugs that block the renin–angiotensin system (RAS) take priority. KDIGO recommends that an angiotensin-converting enzyme inhibitor (ACEi) or an angiotensin II receptor blocker (ARB) be initiated in patients with diabetes, hypertension, and albuminuria, and that these medications be titrated to the highest approved dose that is tolerated. Dual blockade is avoided: the combination of an ACEi with an ARB, or the combination of an ACEi or ARB with a direct renin inhibitor, is potentially harmful. Because blood pressure often needs several drug classes, all 3 classes are often needed to attain BP targets. RAS inhibitors also cause a small early fall in filtration: 2-4 weeks of ACEi/ARB initiation or dose escalation since RAS blockade can induce a transient decrease in the eGFR or a transient increase in serum potassium, so potassium and creatinine need rechecking after starting or changing the dose.

Lipid Management

Statins are the central lipid-lowering drugs. The ADA recommends that for people with diabetes aged 40–75 years at higher cardiovascular risk, high-intensity statin therapy be used to achieve an LDL cholesterol below 70 mg/dL. High-intensity statin therapy should be prescribed to reduce LDL cholesterol by ≥50% from baseline and to obtain an LDL cholesterol of <70 mg/dL (<1.8 mmol/L). Risk is judged by additional factors such as older age, hypertension, dyslipidemia, smoking, chronic kidney disease, or obesity. Because baseline LDL is often unknown before treatment starts, the ADA favors an absolute LDL goal over a percentage reduction. The 2026 ACC/AHA dyslipidemia guideline goes further in one respect: LDL-lowering therapy is recommended for primary prevention in adults aged 40 to 75 years with diabetes, chronic kidney disease stage 3 or 4, or human immunodeficiency virus, regardless of LDL-C level. KDIGO similarly advises a statin for all patients with type 1 or type 2 diabetes and chronic kidney disease.

Kidney Screening and Diabetic Kidney Disease

Kidney screening combines a urine albumin-to-creatinine ratio with estimated glomerular filtration rate (eGFR). Albuminuria is the more sensitive early marker, and an ACR of 30 mg/g or more signals elevated risk. Treatment choices depend on eGFR thresholds. KDIGO recommends an SGLT2 inhibitor for patients with type 2 diabetes and chronic kidney disease when eGFR is at least 20 mL/min/1.73 m², and metformin can be given when eGFR is at least 30. A nonsteroidal mineralocorticoid receptor antagonist with proven kidney or cardiovascular benefit is suggested for adults with T2D, an eGFR >25 ml/min per 1.73 m², normal serum potassium concentration, and albuminuria (>30 mg/g) despite maximum tolerated dose of RAS inhibitor. Finerenone is the only agent in that class with such benefit, and it reduced urinary albumin excretion substantially in trials, with a 30% reduction in UACR at 6 months compared to placebo. KDIGO notes that these agents can be added to a RAS inhibitor and an SGLT2 inhibitor, since their benefits appear to be additive.

Antiplatelet Therapy and Integrated Care

Aspirin use depends on whether cardiovascular disease is already present. Aspirin generally should be used lifelong for secondary prevention among those with established cardiovascular disease and may be considered for primary prevention among patients with high risk for ASCVD. In the ADA framework, a daily aspirin dose of 75-162 mg may be considered as a primary ASCVD prevention strategy in patients with diabetes, following a comprehensive risk-benefit discussion with the patient, including discussion around increased bleeding risk. Because the bleeding hazard is real, this decision is individualized rather than routine.

Effective risk reduction usually requires coordination among primary care clinicians, nephrology, cardiology and pharmacists, as well as attention to smoking, diet and physical activity. Each added agent carries cost, monitoring and side-effect burdens, and the combined regimen can become difficult for patients to sustain without structured support.

Care for Special Populations

Youth-onset type 2 diabetes

Type 2 diabetes that begins in childhood or adolescence tends to progress faster than the adult form. The TODAY trial was the first multiethnic, multicenter randomized trial in the United States to test treatments in this group. It enrolled 699 obese youths aged 10 to 17 with new-onset disease and compared monotherapy with metformin, metformin with rosiglitazone, and metformin with an intensive lifestyle intervention. Treatment failure was defined as hemoglobin A1c (HbA1c) ≥ 8% for at least 6 months. Within the trial, metformin plus rosiglitazone was associated with a significantly lower occurrence of primary outcome (failure rate 39%) compared to metformin alone (failure rate 52%), while adding intensive lifestyle change produced an intermediate result that was not statistically distinct from metformin alone.

Durability was the central problem. There was a decline in beta cell function over time in the TODAY study, regardless of treatment group, and glycaemic control failure rates and decline in beta cell function were more than two times higher in the TODAY study than in comparable adult trials. Analysis suggested that residual beta cell function, not insulin sensitivity, was identified as the primary determinant of glycaemic control. The lifestyle arm also disappointed: an aerobic exercise intervention did not attenuate hypertension or microvascular complications in youth with T2DM, and only 53.6% of participants in the TODAY trial met the physical activity target.

Long-term follow-up in TODAY2 showed that complications accumulate early. 60% of participants in the study developed at least one complication by early adulthood, while nearly a third had two or more complications. Clinical investigators have argued for treating this disease more aggressively and earlier, ideally at the pre-diabetes stage. Metformin remains the first-line treatment for youth-onset type 2 diabetes, and many treatment challenges, including the need for insulin escalation, remain unresolved.

Gestational diabetes and intergenerational risk

Gestational diabetes (GDM) is common. It is present in about 2–6% of all pregnancies in Europe. Although maternal glucose tolerance often normalises shortly after pregnancy, the long-term risk is substantial. Approximately 50% of mothers with GDM will develop diabetes within 10 years, making GDM one of the strongest predictors of type 2 diabetes. Known risk markers include pregnancy at an advanced age, insulin treatment during pregnancy, and delivering an overweight baby. Prevention is feasible, since development of type 2 diabetes can be prevented or delayed by lifestyle intervention and/or medical treatment in women with previous GDM, yet systematic follow-up is often missing from routine care.

The effects extend to offspring. In a Korean nationwide birth cohort of about 3.5 million mother–child pairs, GDM without insulin during pregnancy was significantly associated with increased risk (HR, 1.281), with a greater risk among insulin-treated GDM pregnancies (HR, 4.329) for offspring type 2 diabetes. Sibling comparisons in the Pima Indians of Arizona point to in-utero mechanisms: intra-uterine mechanisms make an important contribution to the link between gestational diabetes and offspring greater adiposity, insulin resistance, and type 2 diabetes. The proposed mechanism is that maternal hyperglycemia and resultant fetal hyperinsulinism results in developmental and epigenetic preprogramming of cardiometabolic risk in the offspring, which is one route by which epigenetic change transmits risk across generations.

Older adults

For older people, the main priority is often avoiding harm rather than achieving the tightest control. Most diabetes clinical practice guidelines recommend a strict HbA1c target for healthier older adults and a more relaxed target older adults who are frail, medically complex or functionally impaired. Most clinical practice guidelines place hypoglycaemic risk as central consideration in medication selection in all older adults. One expert consensus suggests that HbA1c <58mmol/mol in those non-frail, pre-frail or mildly frail adults, to 59-64mmol/mol for moderate frailty and 64-69mmol/mol in those with severe frailty and reduced life expectancy.

Deintensification is recommended in specific situations. Deintensification or simplification of complex regimens is recommended for older adults with multiple complications and reduced function or those at end of life. Aggressive lowering with agents that carry a high hypoglycemia risk may be associated with increased mortality in frail patients. Frailty itself changes the picture, because declining body function associated with weight loss and malnutrition may lead to normoglycemia, increased risk of hypoglycemia and reduced body needs of hypoglycemic medications. Cognition adds a further concern: Association of hypoglycemia with subsequent dementia in older patients with type 2 diabetes mellitus. Newer agents also need caution, since the cautious use of the new therapies, GLP-1RA and SGLT-2 inhibitors, is advised to reduce the risk of hypotension, dehydration, weight loss and falls in this vulnerable population. Care plans are therefore individualized around frailty status, cognition and hypoglycemia risk.

Ethnic minorities and socioeconomically disadvantaged groups

Ethnic minority and socioeconomically disadvantaged populations often carry a heavier burden of type 2 diabetes and its complications, and they face more obstacles at each step of care. Barriers commonly include limited access to screening and specialist services, cost of medication and monitoring, language and health-literacy difficulties, and interrupted continuity of care. These inequities are shaped by social determinants of health, income inequality and unequal access to digital tools, and they are addressed mainly through the design of the health system and its financing.

Public Health and Economic Burden

Type 2 diabetes is costly for individuals, health systems and economies, and most estimates rest on a simple method: they compare people with diabetes against people without it. The IDF Diabetes Atlas, for example, uses an attributable fraction approach, combining prevalence estimates, national health expenditure data and an estimated cost ratio between people with and without the disease. The Atlas's 2024 estimate put diabetes-related health expenditure above USD 1 trillion for the first time, up from USD 966 billion in 2021. Roughly 12% of global health spending was attributed to diabetes, and about 43% of adults with diabetes were undiagnosed, which means that the true cost is probably underestimated. Estimates of this kind depend on how well prevalence is measured in low-income countries, where most people with the disease live and where data are sparse, so regional figures carry wider uncertainty than global totals.

Direct and indirect costs

National studies break the burden into direct medical costs and indirect losses. The American Diabetes Association's 2022 analysis, which draws on national surveys, Medicare files and commercial claims, put the total cost of diagnosed diabetes in the United States at USD 412.9 billion, of which USD 306.6 billion was direct medical spending and USD 106.3 billion was lost productivity. Hospital inpatient care and prescription drugs beyond glucose-lowering agents were the largest contributors to direct costs. Care for people with diagnosed diabetes accounted for about one in four US health-care dollars, and people with the disease had medical expenditures about 2.6 times those of people without it. Indirect costs include disability-related unemployment, reduced work output and productivity lost to premature death. Because such studies count only diagnosed cases and omit pain, unpaid caregiving and undiagnosed disease, they are conservative.

Prevention policy and fiscal measures

Population-level prevention has become a central policy focus. Many countries have national diabetes prevention programmes that offer structured lifestyle education to people with prediabetes, and food policy has increasingly targeted sugar-sweetened beverages through taxation. In July 2025 the World Health Organization launched its "3 by 35" initiative, which asks governments to raise the real prices of tobacco, alcohol and sugary drinks by at least 50% by 2035 through health taxes. The WHO argues that these taxes could raise about USD 1 trillion in revenue over a decade while reducing consumption of products linked to noncommunicable diseases, which account for more than 75% of global deaths. Some countries already earmark sugary-drink revenue for health coverage or for programmes on diabetes and other noncommunicable diseases. Taxation is contested by industry and raises questions about its burden on lower-income households, so its effects depend on how revenue is spent and how tax structures are designed.

Global targets and international monitoring

Diabetes is covered by the global commitment to reduce noncommunicable disease mortality. Under the Sustainable Development Goals, target 3.4 calls for a one-third reduction in premature deaths from these diseases by 2030 relative to 2015 levels. Progress is tracked by the WHO and national statistical agencies, with epidemiological surveillance, mortality registries and health-system data as the main inputs. Monitoring is hampered by weak death registration and by the lack of diagnosis data in many countries, so the reported burden often understates the true scale. Coordination between the WHO, the IDF and national governments aims to align targets, but financing for monitoring remains uneven, and the decline in international development aid since the late 2010s has added pressure on budgets for prevention in lower-income countries.

Inequality in access and household finances

The burden falls unevenly. Diabetes is often diagnosed late in low- and middle-income settings, and people in these settings tend to face out-of-pocket costs for insulin, testing supplies and specialist visits. Within countries, social determinants of health such as income, education and place of residence shape who receives timely care and who experiences complications. Where universal-health-coverage is limited, a diabetes diagnosis can push households into financial hardship. At work, the disease reduces labour participation through absenteeism, reduced output and early retirement, which affects workforce productivity and household incomes. Access to digital tools and digital health services adds another layer of unequal access to monitoring and self-management support. Policy responses therefore focus on reducing out-of-pocket spending, expanding primary care and making essential medicines affordable, as well as on the economic case for early prevention.

Historical Development of Knowledge

The earliest known reference to the condition comes from Egypt. The Ebers Papyrus, dated to about 1550 BCE and named after the German Egyptologist Georg Ebers, who bought it in Luxor in 1872, includes remedies for excessive urination. Its key phrase is hard to translate: the word asha can mean either "plentiful" or "often," so scholars still debate exactly which disorder it describes. Around the same period, or somewhat later, Indian physicians noted that some patients' urine tasted sweet and called the disorder madhumeha, or "honey urine." Chinese medicine described a "wasting-thirst" syndrome called xiaoke, and in some Chinese accounts diet was already linked to worsening symptoms. Accounts of who first used the word "diabetes" vary: sources name Apollonius of Memphis around 230 BCE, Demetrius of Apamea in the 1st century BCE, and Aretaeus of Cappadocia, whose clinical description dates to around 100 CE. Medieval and early modern physicians mostly regarded the disease as a disorder of the kidneys.

The sweetness of the urine was the key clue that changed this view. In the 1670s, Thomas Willis at Oxford tasted patients' urine, recognized that its sweetness resembled sugar or honey, and added the Latin word mellitus to the name. Some accounts date his work to 1674 and others to 1675. In 1776, Matthew Dobson showed that the sweetness came from sugar, which pointed to a systemic problem in glucose handling rather than a purely renal one. In 1869, Paul Langerhans described small clusters of distinctive cells in the pancreas, later named the islets of Langerhans. In 1910, the British physiologist Edward Albert Sharpey-Schafer proposed that the pancreas made a missing substance, which he called insulin.

Before 1921, a diagnosis was usually a death sentence, particularly for young people with what is now called type 1 diabetes. The most effective treatment was a very strict low-carbohydrate diet, which could prolong life for a few years at most. In Toronto in 1921, Frederick Banting and Charles Best, working in the laboratory of John Macleod, obtained an extract that lowered blood glucose in diabetic dogs. Banting had first tied off the pancreatic ducts to destroy the digestive tissue and keep the islets. James Collip then refined the extract for human use. On 23 January 1922, 14-year-old Leonard Thompson became the first patient treated with purified insulin. The 1923 Nobel Prize went to Banting and Macleod, who shared their awards with Best and Collip, respectively. Commercial production by Eli Lilly and later by Novo Nordisk made insulin widely available within a few years.

Early insulin therapy soon revealed that patients differed in their response. Animal-derived insulin often provoked antibodies, and some patients needed very large doses. In 1936, the British physician Harold Himsworth proposed dividing diabetes into insulin-sensitive and insulin-insensitive types, a distinction that anticipated the later separation of type 1 and type 2 diabetes. The decisive step came in the 1950s, when Solomon Berson and Rosalyn Yalow at the Bronx Veterans Administration Hospital developed a radioimmunoassay that could measure insulin in plasma. Their 1960 papers showed that many adults with diabetes had higher, not lower, circulating insulin than non-diabetic people. They concluded that these patients' tissues responded poorly to insulin. Yalow received the Nobel Prize in 1977; Berson had died in 1972 and was not included. Gerald Reaven's 1988 Banting Lecture later framed insulin resistance as a central feature of a clustering of metabolic abnormalities, including hyperglycemia, high blood pressure, dyslipidemia and obesity.

From the 1990s onward, large randomized trials turned these physiological insights into evidence for treatment and prevention. The Diabetes Control and Complications Trial (1993) showed that intensive glucose control reduced microvascular complications in type 1 diabetes. The UK Prospective Diabetes Study (UKPDS, 1998) extended this finding to type 2 diabetes and reported that tighter blood pressure control reduced diabetes-related deaths and complications. The Diabetes Prevention Program (2002) found that intensive lifestyle change reduced progression from prediabetes to diabetes by about 58%, and metformin by about 31%. These results established glycemic control, blood pressure control and prevention as the core strategies that still guide clinical practice.

Open Questions and Research Frontiers

Why beta cells fail, and whether the loss can be reversed

Type 2 diabetes combines insulin resistance with a failure of insulin secretion, but the order of events is still debated. Beta-cell mass is reduced and secretory function is impaired, yet it is not clearly understood whether the loss of mass drives the dysfunction or follows from it. Researchers also note that either scenario can contribute to disease, depending on the individual. This leaves open why some people with insulin resistance eventually exhaust their beta cells while others compensate for decades.

One shift in thinking is that beta cells may lose their identity rather than simply die. Evidence suggests they can dedifferentiate into nonfunctional endocrine progenitor-like cells or trans-differentiate into other endocrine cell types, and that this process is not an irreversible process. Regeneration research has focused on three routes: neogenesis via stem cells, the duplication of existing β cells, and transdifferentiation of existing pancreatic progenitor cells. The obstacle is biological. Human beta cells normally undergo replication only in the first few years of life, and it is still challenging to promote the effective proliferation of beta cells in humans, even though this has worked in animal models and cell lines. Pushing cells to divide also carries risk, since interference with protective mechanisms may induce tumorigenesis.

Mechanisms of remission after bariatric surgery

Bariatric surgery can bring type 2 diabetes into remission, and the effect is not simply a product of weight loss. After Roux-en-Y gastric bypass, glucose control often improves within 1 week, when significant weight loss has not yet taken place. Gastric banding, which produces little early weight change, is associated with a slower improvement, which suggests that rerouting the gut contributes independently of weight loss . Proposed mechanisms include calorie restriction, improved β-cell function, improved insulin sensitivity, and alterations in gut physiology, bile acid metabolism, and gut microbiota. Surgery also changes circulating hormones, gut microbiota, bile acids, and the relative contributions of these changes remain unresolved. One energy-based model proposes that the sustained energy deficit removes the energy excess and induces a persistent energy deficit, but other authors state that a consensus remains to be established regarding the underlying mechanisms.

Long-term management raises its own questions. Most patients keep their weight loss and metabolic gains, but small scale studies have shown weight regain and diabetes relapse, the mechanisms of which remain unknown. Clinicians therefore cannot yet predict which patients will keep remission, and this matters for how long follow-up should last and whether remission can be induced by non-surgical means.

Gut microbiome, metabolomics and digital tools

The gut microbiome is one of the most active areas of investigation. Early cross-sectional studies showed reduced gut microbiome diversity in type 2 diabetes, but cause and effect were unclear. Prospective data are now emerging: a Swedish cohort of 4,685 adults found that the gut microbiome measured years before diagnosis predicts future type 2 diabetes risk. Causal inference is more contested. A Mendelian randomization study found the causal link between gut microbiome and T2DM was absent after multiple-testing correction. After bariatric surgery, microbial changes appear quickly, but most studies didn't analyze microbiome in the first post-operative weeks in which the improvement in diabetes takes place. Transfer experiments are more suggestive: two independent studies exhibited improved metabolism following FMT from post-bariatric surgery humans and mice donors.

Metabolomic profiling offers a complementary route. Untargeted metabolomics has identified circulating amino acids, lipids, and other metabolites that are prospectively associated with T2D risk, which may help connect microbial metabolism to host insulin sensitivity. Yet the translation to practice is incomplete: despite a huge number of association studies, no microbiome biomarkers have yet been implemented into clinical practice. Digital tools for risk prediction and personalized treatment face similar hurdles. Validation across diverse populations, data quality from consumer devices and equitable access are unresolved, and these concerns connect to the digital divide.

Evidence gaps for subgroups and newer therapies

Much of the evidence base for newer drugs comes from trials of defined duration and population. Long-term safety beyond those periods, the response of youth, older adults and under-represented ethnic groups, and whether early gains in glycemia translate into lasting reductions in cardiovascular and kidney events all remain open questions. Cost-effectiveness is also uncertain because prices, health-system structures and payment models differ widely, so conclusions from one setting may not transfer to another. Closing these gaps will likely require pragmatic trials, long-term registries and well-designed studies of the biological processes outlined above.

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