Vitamins and minerals - recommended and maximum daily doses (from all sources)

Vitamin C - 90mg men, 75mg women (max 2,000mg) Vitamin E - 15mg men and women (max 1,000mg) Selenium - 55mcg men and women (max 400mcg)

And the experts said that large doses of some supplements may cause health problems rather than protect health.

They said that the belief that large doses of vitamins were of extra benefit was a myth.

A British advisory expert group reviewing vitamin dose levels is expected to take account of the American recommendations.

The group, set up by the Ministry of Agriculture last year, is due to report to the new Food Standards Agency in April 2001 with its own upper limit guidelines.

Antioxidant supplements are said to reduce the chances of suffering cancer, heart disease, diabetes, Alzheimer's and other illnesses by reducing the number of molecules called free radicals in the body.

The US National Academy of Sciences panel looked at the evidence for the effectiveness of four of the most popular antioxidants, vitamins C and E, selenium, and beta carotene, which is turned into vitamin A in the body.

It concluded there was nothing in the scientific literature to suggest that high doses of these supplements could protect against illness.

Excess beta carotene, in particular, was known to increase the risk of cancer in some people, especially smokers.

The panel set no limits for beta carotene, holding the view that it should not be taken at all other than by people with a vitamin A deficiency.

At least one study has suggested that very large vitamin C doses can cause rather than prevent oxidative damage to DNA in cells.

The panel set a 2,000 milligram daily upper limit for vitamin C from a combination of food and supplements.

Stroke damage

An upper limit for adults of 1,000 milligrams was set for vitamin E because people taking doses above this level were thought to run a risk of stroke.

However the recommended daily intake of vitamin E was raised from its old 1989 level of 10 milligrams for men and eight for women, to 15 milligrams.

Selenium was also given an upper limit for the first time, of 400 micrograms per day.

A spokesman for the Food Standards Agency said: "There's a lot of information around that suggests some supplements may be harmful if used to excess, but it remains to be seen whether that is actually proven. The jury is still out in many cases.

"Generally the advice is that if you eat a balanced diet you don't need supplements unless you are deficient in some way."

Recommended vitamin C levels can easily be achieved by eating five servings of fruit and vegetables per day, said the American experts.

The chief source of vitamin E should be food such as nuts, seeds, liver and leafy green vegetables, said the panel.

Sheila Kelly, Executive Director of the Proprietary Association of Great Britain, which represents manufacturers of vitamins and minerals, said: "The ppossible danger is in taking mega-doses of supplements, many times higher than the recommended daily allowance.

"Responsible manufacturers of health supplements would never claim that huge doses of health supplements can prevent , treat or cure disease."