What has the research found?It was already known that if you carry a certain faulty gene - known as ApoE4 - your risk of Alzheimer's is increased.
The new research compared brain scans of people with ApoE4, with brain scans of people without it.
They found that people with ApoE4 had changes in their brain activity decades before they had any symptoms of Alzheimer's. Their brains were basically working harder all the time - even when they were resting.
What does this mean?Experts think this could mean that one of the causes of Alzheimer's is the brain being over-worked and becoming exhausted.
Does this mean there's now a cure for the disease?Unfortunately not, but it's a step closer to developing a test that could tell if a person is more at risk of Alzheimer's.
People who are more at risk could then be offered early treatment and lifestyle advice to slow down Alzheimer's developing.
If I have the gene will I definitely get Alzheimer's?No, it's a complicated disease that can be caused by genetics and by environment - or by a mixture of the two.
If you do have the gene you have a higher risk of getting Alzheimer's, but it's not definite. People without the gene could still get Alzheimer's.
What is the difference between Alzheimer's and dementia?Dementia is a loss of mental ability and other related symptoms. It usually develops gradually.
Alzheimer's is actually a disease that causes dementia. It causes the brain to shrink, and brain nerve fibres and fluids reduce. This causes changes in brain activity - but it's not exactly clear how this causes dementia yet.
How common is it?Dementia affects 70, 000 people in the UK. Alzheimer's causes 6 out of 10 cases of dementia.
What do the experts say?Professor Clive Ballard, director of research at the Alzheimer's society says: 'This study paves the way for further research that could help us understand how brain function in younger adults may contribute to the development of Alzheimer's disease later in life.'
Where to next?- Get more facts and information Alzheimer's and dementia
- New memory clinics to treat dementia
- New drugs for treating Alzheimer's