Definition
Dementia is a collective term rather than the name of a single disease. Clinicians apply it to a set of conditions in which the brain's capacity to think, remember and reason declines more than normal ageing would explain. Dementia is a syndrome, usually chronic or progressive in nature, that leads to deterioration in cognitive function beyond what might be expected from the usual consequences of biological ageing. The underlying cause is a brain disorder, and the same outward syndrome can arise from several different pathologies.
Symptoms and course
Memory, thinking, orientation, comprehension, calculation, learning capacity, language and judgement can all be affected. Awareness of the surroundings, by contrast, is generally preserved: consciousness is not affected. Changes in mood, emotional control, behaviour or motivation frequently appear alongside the cognitive losses and, less often, come first.
Early indicators include forgetting recent events and people's names, becoming confused at home, and increasing difficulty in communicating. Behavioural changes such as wandering or repeated questioning may also appear. The late stage of dementia is one of near total dependence and inactivity.
Although the condition is concentrated in later life, it is not a normal part of growing old. Dementia mainly affects older people, but it is not an inevitable consequence of ageing. When symptoms begin before age 65, the case is called young-onset dementia; the WHO notes that this accounts for up to 9% of all dementia cases.
Causes and main types
Dementia results from a variety of diseases and injuries that affect the brain. Because the causes differ, the types are usually grouped by the underlying pathology.
Alzheimer's disease
Alzheimer's disease is the most frequent form. The WHO estimates that it may contribute to 60–70% of cases. Its hallmark is the accumulation of abnormal deposits of proteins, forming amyloid plaques and tau tangles throughout the brain. See protein for background on protein misfolding.
Vascular dementia
Vascular dementia is the second most common type of dementia. It is caused by disruption of blood flow to the brain, for example by clots or bleeding, and is closely tied to stroke and cardiovascular health. Early signs often include difficulty with planning and concentration, sometimes with brief episodes of sudden confusion. See vascular dementia for details.
Lewy body dementia
Lewy body dementia involves abnormal deposits of the alpha-synuclein protein, which affect the brain's chemical messengers. Symptoms can include fluctuating attention, hallucinations, delusions and problems with movement and sleep. It is closely related to the disease process behind Parkinson's disease.
Frontotemporal dementia
Frontotemporal dementia is less common overall. It is sometimes called Pick's disease, and common early symptoms include changes to personality and behaviour and/or difficulties with language.
Mixed and rarer forms
Several pathologies often coexist. The most common type of mixed dementia is Alzheimer's disease and vascular dementia. Rarer forms also exist; in the UK, about 1 in 20 people living with dementia have a rarer type.
Epidemiology
In 2021, 57 million people were living with dementia worldwide, over 60% of whom live in low- and middle-income countries. Every year, there are nearly 10 million new cases. Dementia is currently the seventh leading cause of death and one of the major causes of disability and dependency among older people globally.
Projections are considerably higher. One analysis cited a rise from about 55 million people to 78 million in 2030 and 139 million by 2050. Prevalence is expected to grow mainly because of population ageing, and the burden falls disproportionately on public-health systems in lower-income countries.
Risk factors
Age is the strongest known risk factor. Other established factors include high blood pressure, high blood sugar, being overweight or obese, smoking, drinking too much alcohol, physical inactivity, social isolation, depression, low educational attainment, cognitive inactivity and air pollution.
The WHO and the Lancet Commission on dementia have tried to quantify how much of the risk is modifiable. The 2020 Lancet Commission report found that together the 12 modifiable risk factors account for around 40% of worldwide dementias, which consequently could theoretically be prevented or delayed. The 2024 update expanded the list to 14 factors and suggested the proportion could be as high as 45%. The two new risk factors are untreated vision loss and high LDL cholesterol. Hearing loss has been identified as a notable midlife factor; in the 2020 analysis it was linked to 8% of cases.
Genetics also matter. The apolipoprotein E4 (ApoE-4) allele carries the strongest genetic risk for Alzheimer's disease, and it can change how environmental exposures affect the brain. Genetic and environmental factors thus interact rather than acting independently.
Diagnosis and treatment
Diagnosis is clinical. It typically combines a history from the patient and a relative or carer, cognitive testing, neurological examination, and tests to rule out reversible causes such as vitamin deficiency, thyroid disease or medication effects. Imaging and, increasingly, blood-based biomarkers are used to support the diagnosis, particularly in Alzheimer's disease.
For most forms of dementia, no treatment reverses the underlying brain damage. Medications mainly aim to ease symptoms. Anti-amyloid antibody drugs have been approved for early Alzheimer's disease in several jurisdictions; their benefit is modest, and they carry risks, including brain swelling and bleeding, which require monitoring. Non-drug care, support for carers and management of related conditions form a central part of care.
Social and economic impact
In 2019, dementia cost economies globally US$ 1.3 trillion, approximately 50% of these costs are attributable to care provided by informal carers such as family members and close friends, who provide on average 5 hours of care and supervision per day. Cost estimates vary with methodology: one analysis gives a 2019 figure of about US$263 billion, and projects a rise to over US$1.5 trillion by 2050. The WHO's Global action plan on the public health response to dementia 2017–2025 sets out priorities including awareness, risk reduction, diagnosis, carer support and research, and is monitored through the Global Dementia Observatory.
Open questions
The causes of most late-life dementia are still incompletely understood. Late-life dementia results from neurodegeneration linked to chronic disease processes, though the driver of these changes remains unclear. The population-attributable estimates above are theoretical; they do not guarantee that a given individual's risk can be lowered by a specific amount. Some studies find that correlated Lancet Commission risk factors, when considered together, accounted for relatively little of the variance in plasma NfL, GFAP, or MCI in a midlife male cohort, suggesting that much of the variation in risk remains unexplained. Ongoing research focuses on earlier biomarkers, disease-modifying treatments and the interaction between genetic and lifestyle factors.
References
- WHO updates fact sheet on Dementia (20 September 2022)communitymedicine4asses.wordpress.com
- who dementia statisticsdementiaresearcher.nihr.ac.uk
- WHO Updates Fact sheet on Dementia (31 March 2025)communitymedicine4asses.wordpress.com
- Dementiawho.int
- Infographic: Understanding Different Types of Dementiania.nih.gov
- Types of dementiaalzheimers.org.uk
- Dementia prevention, intervention, and care: 2020 report of the Lancet Commission - The Lancetthelancet.com
- 14 Risk Factors That May Help Prevent or Delay Dementiaaarp.org
- Lancet Commission on dementia prevention, intervention and care identifies 12 modifiable risk factors accounting for 40% of dementiasalzheimer-europe.org
- Life Course Modifiable Risk Factors for Dementia Stratified by ApoE-4 Statusncbi.nlm.nih.gov
- WHO/Yoshi Shimizuwho.int
- Neurophysiological Correlates of Modifiable Dementia Risk Factors in Cognitively Unimpaired Older Adultsbiorxiv.org
- Associations of Lancet Commission risk factors for Alzheimer's disease with blood‐based biomarkers and mild cognitive impairment from midlife to early old agencbi.nlm.nih.gov
- A cross-country analysis of episodic memory and (potentially) modifiable risk factors of dementiamedrxiv.org