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Dementia is not caused by a single thing. It is caused by diseases that damage brain cells, and which disease is responsible determines the type of dementia a person develops, how it progresses, and how it is best cared for.
Around 1.01 million people in the UK are estimated to be living with dementia in 2025. It is the country's leading cause of death, accounting for more than one in ten of all UK deaths recorded in 2024.
Understanding what causes dementia also reveals what may help reduce the risk. The 2024 Lancet Commission on Dementia Prevention, Intervention, and Care found that up to 45% of dementia cases worldwide are linked to factors that people can potentially do something about across the course of a lifetime.
Is dementia a normal part of ageing?
No. Dementia is caused by disease, not by ageing itself. Age is the single biggest risk factor, and the risk roughly doubles every five years after the age of 65, but most older people do not develop dementia. It is a medical condition, not an inevitable stage of life.
This distinction matters. It shapes how dementia is understood, diagnosed, and supported by families and care professionals alike.
What are the main types of dementia and what causes each?
There are several different diseases that cause dementia. Each affects the brain differently and produces a different pattern of symptoms.
Alzheimer's disease
Alzheimer's disease is the most common cause of dementia, responsible for 60 to 70% of all cases. It is caused by an abnormal build-up of two proteins in the brain. One, called amyloid, forms clumps (plaques) around brain cells. The other, called tau, forms tangles inside them. These deposits interfere with how brain cells communicate, damage them over time, and eventually cause them to die.
The areas of the brain involved in memory are typically the first to be affected, which is why short-term memory loss is usually one of the earliest signs. As the disease progresses, it spreads to other parts of the brain and affects language, reasoning, spatial awareness, and eventually physical function.
The exact reason why amyloid and tau build up in the first place is not yet fully understood. Genetic factors are known to play a role, though most Alzheimer's cases are not directly inherited.
Vascular dementia
Vascular dementia is the second most common type, affecting around 10 to 20% of people with dementia. It is caused by reduced or interrupted blood supply to the brain. This most commonly happens because of a stroke, a series of small strokes (sometimes called TIAs or mini-strokes), or the gradual narrowing of small blood vessels in the brain.
When brain tissue is starved of blood, even briefly, cells die. The resulting dementia can affect different abilities depending on which part of the brain is damaged, and may progress in noticeable steps rather than the more gradual decline typical of Alzheimer's.
Because vascular dementia is directly linked to heart and blood vessel health, many of its risk factors are the same as those for stroke: high blood pressure, smoking, diabetes, high cholesterol, and obesity.
Our article on vascular dementia vs Alzheimer's: what's the difference explains the two conditions side by side.
Lewy body dementia
Lewy body dementia accounts for around 5 to 10% of cases. It is caused by abnormal deposits of a protein called alpha-synuclein forming inside nerve cells in the brain. These deposits are known as Lewy bodies, and they disrupt how the brain processes and sends signals.
Lewy body dementia shares some features with both Alzheimer's and Parkinson's disease. It often causes visual hallucinations, fluctuating alertness, sleep disturbances, and problems with movement, alongside memory and thinking difficulties. It is often underdiagnosed because its symptoms can look like other conditions.
Frontotemporal dementia
Frontotemporal dementia (FTD) is less common overall but is one of the more frequent causes of dementia in people under 65. It affects the frontal and temporal lobes of the brain, which are responsible for personality, behaviour, and language. As these areas deteriorate, the changes show up first in how a person behaves, communicates, or relates to others, rather than in memory loss.
Several different abnormal proteins can be involved in FTD. It also has a stronger genetic link than most other types: around a third of people with FTD have a family history of the condition.
Mixed dementia
Mixed dementia most commonly refers to a combination of Alzheimer's disease and vascular dementia occurring together. Brain studies have found that many people diagnosed with a single type of dementia in life showed signs of more than one disease process. Mixed dementia is thought to be more common than was previously recognised, and it affects how symptoms present and how care needs to be tailored.
What are the risk factors for dementia?
Risk factors fall into two groups: those that cannot be changed, and those that can be addressed.
Risk factors that cannot be changed
Age is the most significant risk factor. Risk roughly doubles every five years after the age of 65.
Genetics plays a role, but for the vast majority of people it increases risk rather than determines outcome. Directly inherited forms of dementia, where a single faulty gene causes the condition, are rare and account for fewer than 5% of Alzheimer's cases.
Sex is a factor. Women account for approximately two-thirds of dementia cases in the UK, partly because women tend to live longer, though biological and hormonal differences are also thought to contribute.
Ethnicity affects risk too. People from South Asian and Black African and Caribbean communities have a higher risk of vascular dementia, which is partly connected to higher rates of conditions such as high blood pressure and diabetes in these groups.
Risk factors that can be addressed
The 2024 Lancet Commission identified 14 modifiable risk factors. Two of these, untreated vision loss and high LDL cholesterol, were newly recognised in the 2024 update. Together, these factors are estimated to account for up to 45% of dementia cases globally.
The 14 modifiable risk factors, grouped by stage of life, are:
Early life
- Low levels of education
Mid-life
- Untreated hearing loss
- High blood pressure
- Obesity
- Excessive alcohol consumption
- Traumatic brain injury
- High LDL cholesterol (added in 2024)
Later life
- Smoking
- Depression
- Social isolation
- Physical inactivity
- Diabetes
- Air pollution
- Untreated vision loss (added in 2024)
It is important to be clear about what this means. Addressing these risk factors reduces the chances of developing dementia but does not eliminate them. Many people with multiple risk factors never develop dementia. Many people who develop dementia have none of the factors listed above. The value of this research is in understanding where prevention efforts at a population level can make the greatest difference.
"Research increasingly shows that dementia is not simply a matter of genetics or chance. Many of the risk factors sit alongside conditions we already have good reasons to manage: blood pressure, cholesterol, hearing, exercise. Supporting people to address these is part of good care across the lifespan."
Does depression cause dementia?
People diagnosed with depression are more than twice as likely to be diagnosed with dementia later in life. The relationship is not straightforward: depression may affect the brain in ways that increase vulnerability, or it may in some cases be an early sign of the underlying disease process. Either way, getting effective treatment for depression is considered important for reducing dementia risk in later life.
Can a head injury cause dementia?
Traumatic brain injury is a recognised risk factor for dementia, particularly when injuries are repeated or severe. The connection is most clearly seen in contact sports and among people who have experienced multiple concussions. Even a single significant head injury in mid-life is associated with a raised risk later on.
Is dementia hereditary?
For most people, dementia is not directly inherited. Genetic variants such as the APOE-e4 allele can raise the risk of Alzheimer's disease but do not mean it will develop. Directly inherited forms, caused by a single gene mutation, account for fewer than 5% of Alzheimer's cases.
Frontotemporal dementia has the strongest genetic link of the common dementia types. If you have a family history of early-onset dementia, a GP can refer you to a genetics service for guidance.
Can dementia be prevented?
Not entirely. But the evidence that risk can be meaningfully reduced is substantial and growing. Nearly half of all dementia cases may be connected to factors that are, in principle, addressable.
Reducing risk is not the same as preventing the condition. The goal of risk reduction is to delay the onset of dementia where possible and to lower the likelihood of it developing at all. Given how many people are affected, even small shifts at a population level have a significant impact.
How does knowing the cause affect care?
Knowing which type of dementia a person has directly affects how their care is planned. Someone living with Lewy body dementia has specific sensitivities to certain medications that do not apply to someone with Alzheimer's. Vascular dementia requires attention to cardiovascular health alongside dementia care. Frontotemporal dementia often calls for a different approach to communication and managing behaviour.
At Ashberry, our dementia care is built around understanding each person, not just their diagnosis. Our guide to the different approaches to dementia care explains how specialist care is structured in practice.
FAQ
What is the most common cause of dementia? Alzheimer's disease, responsible for 60 to 70% of all dementia cases. It is caused by abnormal protein deposits in the brain, known as amyloid plaques and tau tangles, which damage and destroy brain cells over time.
Can stress cause dementia? There is no proven direct link between stress and dementia. However, chronic stress is associated with depression and high blood pressure, both of which are recognised risk factors. Managing stress well is part of a broader approach to reducing risk.
Does alcohol cause dementia? Excessive alcohol consumption is a confirmed risk factor for dementia. Heavy, long-term drinking can cause a specific form of dementia called Wernicke-Korsakoff syndrome, and also raises the risk of vascular dementia. Moderate drinking is not established as a significant risk at a population level.
At what age does dementia usually start? Most people with dementia are over 65, and the average age of diagnosis is around 80. Younger-onset dementia, diagnosed before the age of 65, affects around 42,000 people in the UK and is more likely to involve frontotemporal dementia or genetically linked forms of Alzheimer's.
Is there a blood test for dementia? There is no single blood test that diagnoses dementia, though blood-based biomarkers for Alzheimer's disease are an active area of research. Diagnosis currently involves a combination of cognitive tests, brain imaging, and sometimes a lumbar puncture or PET scan.
Can dementia be caused by a virus or infection? Research into this is ongoing. Some studies have explored possible links between certain viruses and Alzheimer's disease, but no causal link has been conclusively established. This remains an active and developing area of scientific enquiry.
Supporting someone living with dementia
If someone you love has been diagnosed with dementia, understanding the cause is just the beginning. Questions about where and how they should be cared for, how the condition is likely to progress, and when specialist dementia care becomes the right option are all part of what lies ahead.
Our guides on when someone with dementia should go into a care home and moving into a dementia care home are written to help families think through those decisions clearly, at their own pace.
If you would like to talk to us about dementia care at Ashberry, we are always happy to listen. Make an enquiry and a member of our team will be in touch.
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