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What causes Alzheimer's disease?

Alzheimer’s disease is caused by parts of the brain wasting away (atrophy), which damages the structure of the brain and how it works.

It is not known exactly what causes this process to begin, but people with Alzheimer’s disease have been found to have abnormal clumps of protein (called amyloid plaques) and bundles of protein fibres (called tau tangles) in the brain.

These interfere with the ability of neurons (nerve cells) to communicate with one another, and gradually destroy them. Over time, this damage spreads to other areas of the brain, such as the grey matter (responsible for processing thoughts) and the hippocampus (responsible for memory).

Over time, this damage spreads to other areas of the brain, such as the grey matter (responsible for processing thoughts) and the hippocampus (responsible for memory).

Risk factors

It is still unknown what actually causes the deterioration of brain cells, although there are several things known to affect your risk of developing Alzheimer’s disease. These are described in more detail below.


Age is the greatest factor in the development of Alzheimer’s disease. The likelihood of developing the condition doubles every five years after you reach 65 years of age. However, sometimes younger people can develop Alzheimer’s disease. This is called ‘younger onset dementia’.

Family history

Alzheimer’s disease can also be inherited (run in the family), although the risk is only marginally higher than that of someone who has no family history of the condition.

In cases where Alzheimer’s disease is inherited, the symptoms usually start to develop at a relatively early age (between 35 and 60 years of age).

Down syndrome

People with Down syndrome are at a higher risk of developing Alzheimer’s disease.

This is because people with Down syndrome have an extra copy of chromosome 21, which contains a protein thought to contribute to the development of Alzheimer’s disease.

Whiplash and head injuries

People who have had a severe head injury, or severe whiplash (a neck injury caused by a sudden movement of the head forwards, backwards or sideways), have been found to have a higher risk of developing Alzheimer’s disease.

Lifestyle and health factors

Research shows that several lifestyle factors and health conditions – particularly those linked with cardiovascular disease – can increase your risk of Alzheimer’s disease. These include:

You can help reduce your risk by quitting smoking (if you are a smoker), eating a healthy balanced diet, and having regular health tests as you get older. It is also important to keep as active as possible both mentally and physically to help reduce the risk of developing Alzheimer’s disease.

Read more about Alzheimer’s disease prevention.

Last reviewed: May 2017

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