Scientists have developed what they claim is a 15-minute online test which can help detect the early signs of Alzheimer's disease.

A team at Oxford University has developed the online quiz called the Cognitive Function Test which it claims could help diagnose the most common form of dementia perhaps years earlier than it might normally be spotted.

To take the test, go to 'www.foodforthebrain.org'. It has three sections which use computer-based tasks and games to measure different components of memory.

However, the test is not intended to replace checks with a doctor and it is intended that they will continue to be done to check the diagnosis is correct, 'The Daily Telegraph' newspaper reported.

The quiz will provide an instant result and could either set people's minds at rest or encourage them to act sooner than they might have to visit their doctor. It could also help some people who feel a stigma to admitting they are suffering memory problems, say the scientists.

It will also provide guidance on lifestyle and diet which could also slow the development of the condition.

In fact, the test, which is free to take, follows a significant study published last year which credited a vitamin pill with cutting brain shrinkage linked to the disease by up to five times.

The study showed the vitamin pill to be most effective when taken early but because people who are apparently healthy have no way of telling if they might benefit, the team created the test.

Prof David Smith, an expert, said: "Alzheimer's is a preventable disease, not an inevitable part of the ageing process. The trick is to identify decline in memory function as early as possible and take necessary prevention."