Vexed vitamins

Vexed vitamins nobel laureate Linus Pauling, who died at the age of 93, consistently extolled the benefits of vitamin c . He was said to stir 18 gramme of the vitamin into his daily orange juice. Last April, however, researchers at the University of Leicester, uk , reported that a supplement of as little as 500 milligrammes of vitamin c a day may produce free radicals that can damage dna and cause cancer. Many people pop pills containing thousands of milligramme of the same vitamin, hoping to prevent cancers or ward off the common cold.

Long regarded as harmless, overdoses have come under close scrutiny after two large studies showed that beta-carotene can increase the risk of cancer. Many European countries have already laid down the maximum safe levels for vitamin tablets that are sold to the public. But what should be the maximum limit?

There is a lack of data and the studies that have been carried out frequently contradict each other. Antioxidants can neutralise free radicals and they have been touted as cure-alls for a whole range of diseases. But the evidence on the benefits of antioxidants is ambiguous. A study conducted by the National Cancer Institute in the us and Finland's National Public Health Institute tested the hypothesis that antioxidants would help prevent cancer in smokers.

Nearly 29,000 male Finnish smokers were recruited and divided into four groups. From 1985 to 1993, one group was given a daily pill with 50 milligramme of alpha-tocopherol (a form of vitamin e ), the second took 20 milligramme of beta-carotene and the third took both vitamins, and the rest took a placebo. The risk of cancer among the group on the beta-carotene supplement increased by 16 per cent. "It was a huge shocker to the whole field,' says Susan Taylor Mayne of Yale University. Further analysis of the data showed that heavy smokers and people who drank alcohol seemed worst affected.

Mayne believes that oxidising gases in cigarette may degrade beta-carotene and produce harmful byproducts in the lungs. But John Hathcock of the Council for Responsible Nutrition in Washington, which represents the manufacturers of supplements, argues that "Betacarotene is safe for everyone except long-term smokers who continue the habit while they are taking beta-carotene'. Scientists think that vitamin e prevents free radicals from oxidising low-density lipoprotein, which contributes to heart disease. But too much vitamin e can also promote bleeding.

"Some of the studies have seen a modest increase in haemorrhage-related strokes,' says Manfred Steiner of the East Carolina University School of Medicine in Greenville, North Carolina.