For many years it has been widely accepted that a diet rich in fruit and vegetables is healthy and can protect against illnesses like heart disease and reduce the risk of cancer.

As a result of this scientists have worked hard to look for chemicals in plants which might be the reason for these benefits.

One group of plant chemicals that have been suggested as being beneficial are the antioxidants. Antioxidants remove harmful chemicals, called free radicals, from the body. Free radicals can damage the DNA in the cell's nucleus and this might lead to cancer formation. Antioxidants are found in vegetables like broccoli, cauliflower, brussels sprouts and cabbage.

Clinical trials are underway in a number of countries to see whether giving supplements of antioxidants in the diet might help prevent heart disease and cancer.

One of these studies has published its results. Over 20,000 people between the ages of 40 to 80 were divided into two groups. One group received daily doses of three antioxidants: vitamin C, vitamin E and beta-carotene, for five years, the other group received placebo tablets with no antioxidants.

The study looked at the number of people who got coronary artery disease, strokes, diabetes or cancer. Overall there was no difference between the two groups. The people taking the antioxidants had the same risk of developing any of these illnesses, including cancer, as those who had no dietary supplements.

The study did show that there was no obvious harm from taking the antioxidants.

Although this was a large trial it still is not possible to say for certain that antioxidants don't help prevent cancer and the results of other studies will help answer this question once and for all. For the moment, however, there is no strong evidence of a benefit from taking these particular dietary supplements although there is also no evidence that they do any harm.

Reference:

• Heart Protection Study Collaborative Group. MRC/BHF heart protection study of antioxidant vitamin supplementation in 20 536 high-risk individuals: a randomised placebo-controlled trial. The Lancet, 2002; 360: 23-33.