Alzheimer’s is a disease that causes dementia. It is the most common cause of dementia, accounting for about two-thirds of cases in older people.

What is Alzheimer’s disease?

Alzheimer’s disease is the most common cause of dementia, affecting around six in every 10 people with dementia.  Alzheimer’s may also occur with other types of dementia, such as vascular dementia or dementia with Lewy bodies. You might hear this called ‘mixed dementia’.

Alzheimer’s becomes more common with advancing age, but it’s not a normal part of ageing. The majority of people who develop the disease are over the age of 65.

More rarely, Alzheimer’s can affect younger people. It’s thought that over 42,000, or around 5% of people with Alzheimer’s are under 65. These rare cases of the disease are called early-onset Alzheimer’s.

In Alzheimer’s disease, changes occur in the brain that go beyond those associated with normal ageing. These changes include the build-up of two proteins, called amyloid and tau. Although researchers don’t yet have a complete understanding of what triggers Alzheimer’s, research suggests that both proteins are involved in driving the disease. As Alzheimer’s progresses, more and more nerve cells in the brain become damaged. This damage leads to the symptoms of Alzheimer’s.

With our help, researchers are learning more about why these proteins build up in the brain and how they damage nerve cells. Research is underway to understand more about what happens in the brain during Alzheimer’s and find new ways to treat the disease.

What is Alzheimer's disease?

Find out more about the symptoms and causes of Alzheimer's disease, and the treatments currently available.

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Alzheimer’s Research UK has a wide range of information about dementia. Order booklets or download them from our online form.

This information was updated in May 2018 and is due for review in May 2020. It does not replace any advice that doctors, pharmacists or nurses may give you. Please contact us if you would like a version with references.

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