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Causes - Alzheimer's disease

Alzheimer's disease is caused by a build-up of brain protein inside and around brain cells. This damages and eventually kills the brain cells.

One of these proteins is called amyloid. Amyloid can build up and create plaques around brain cells. The other protein is tau. When tau builds up it can cause tangles inside brain cells.

It's not known what causes this process to begin. But it begins many years before symptoms appear.

There's also a decrease in chemical messengers (neurotransmitters). These send messages, or signals, between brain cells.

Over time, as the brain cells die, areas of the brain shrink. The first areas usually affected are responsible for memories.

The first symptoms may not involve your memory. They could be problems with your vision or language.

Increased risk

Several things can increase your risk of developing Alzheimer's disease.


Age is the single most significant factor. The chance of developing Alzheimer's disease doubles every 5 years after you reach 65.

Older people are not the only ones at risk of developing the disease. Around 1 in 20 people with the condition are under 65. This is early onset Alzheimer's disease and it can affect people from around the age of 40.

Family history

Your genes can increase the risk of developing the disease. But the actual increase in risk is small if you have these particular genes.

In some families, Alzheimer's disease is caused by the inheritance of a single abnormal gene. In these cases, the risks of it being passed on to children are much higher.

Down syndrome

People with Down syndrome have a much higher risk of developing Alzheimer's disease.

The genetic abnormality that causes Down syndrome also causes a build-up of amyloid. This leads to Alzheimer's disease in most people with Down syndrome.

Head injuries

People who have had a severe head injury may be at higher risk of developing Alzheimer's disease. But more research is still needed in this area.

Cardiovascular disease

Cardiovascular disease involves the heart or blood vessels. Many lifestyle factors linked with cardiovascular disease can increase your risk.

These include:

  • smoking
  • obesity
  • diabetes
  • high blood pressure
  • high cholesterol

You can help reduce your risk of cardiovascular disease by:

  • stopping smoking
  • eating a healthy, balanced diet
  • leading an active life, both physically and mentally
  • losing weight if you need to
  • drinking less alcohol
  • having regular health checks as you get older

These risk factors also increase the risk of vascular dementia. This is caused by poor blood supply in the brain. Many people with Alzheimer's disease also have vascular dementia.

Other things that might cause Alzheimer's

There are other things that also slightly increase the risk.

These include:

  • hearing loss
  • untreated depression
  • loneliness or social isolation
  • an inactive lifestyle

It is not your fault if you get Alzheimer's disease. In most cases, it is caused by a combination of:

  • genetics
  • lifestyle
  • environment
  • old age

You can reduce your chances of getting Alzheimer's disease by giving up smoking. But some people will develop it even if they are as healthy as they can be.

Content supplied by the NHS and adapted for Ireland by the HSE

Page last reviewed: 1 September 2022
Next review due: 1 September 2025