Scientists are expecting a low-cost supplement to stop the progress of Alzheimer's disease after a trial showed that deterioration in patients stopped while they took it. Resveratrol, a compound that occurs naturally, is found in raspberries, red grapes, dark chocolate and red wine.

Quantities in these foods are small, but high-dose supplements could be bought over the counter from health food shops by spending only a few pounds. In addition to that, purer forms could be purchased from pharmacists.

Scientists carried out the trial on 119 people having mild to moderate Alzheimer's. In the trial, 1g of high-grade resveratrol was given to patients two times a day for 12 months, whereas a control group was given a placebo.

In general, as the disease progresses, the level of a protein, Abeta40, falls in the blood. However, those who took the supplement, showed no change in the level.

It was found that patients taking the placebo showed reduced levels of Abeta40 and did not show any improvement in cognitive tests. As per researchers, the trial is too small, so it could not be advised that whether people should start taking the supplement. According to them, the findings are "very interesting" and it is required to do further work.

According to Dr Scott Turner, director of the memory disorders programme at Georgetown University Medical Centre, in Washington DC, "Number one, we found that resveratrol was safe in older people with Alzheimer's disease and number two, it looked like it may have had a beneficial effect on biomarkers and disease progression".