Alzheimer's disease is caused by a build-up of normal brain protein inside and around brain cells. This damages and eventually kills the brain cells. One of the proteins involved is amyloid. Deposits of these form plaques around brain cells. The other protein is tau, deposits of which form tangles within 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, different 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

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 a few 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's syndrome

People with Down's syndrome have a much higher risk of developing Alzheimer's disease. The genetic fault that causes Down's syndrome also causes a build-up of amyloid plaques. This lead to Alzheimer's disease in most people with Down's syndrome.

Head injuries

People who have had a severe head injury may be at higher risk of developing Alzheimer's disease. But much 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 by:

• stopping smoking
• eating a healthy, balanced diet
• leading an active life, 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 things. These include:

• genetics
• lifestyle
• environment
• old age

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