A 15-minute online test has been developed to reveal early signs of Alzheimer's disease.
The free quiz was developed by mental health experts and is aimed at 50 to 70-year-olds who are worried about memory decline.
The interactive test provides an immediate result and advice about lifestyle and diet changes. Those at risk are given a letter for their GP.
Professor David Smith, of Oxford University, said: "Alzheimer's is a preventable disease, not an inevitable part of the ageing process.
"Rather than leaving it until too late, the trick is to identify any decline in memory function as early as possible and take the necessary prevention steps."
Research shows poor diet and a bad lifestyle are linked to memory decline and the risk of Alzheimer's.
Three in 10 over-70s have impaired memory, and potentially 75% of these will develop Alzheimer's or some form of dementia within five years.
"Only about one in a hundred cases of Alzheimer's is caused by genes," said Prof Smith.
"As long as decline in memory function is identified early, research has shown that a combination of specific B vitamins, dietary and lifestyle changes, can greatly reduce the rate at which your brain shrinks, and your memory worsens."
Visit www.foodforthebrain.org to take the test.
