EVERY day, about 10 million Britons take almost £1m worth of vitamin supplements to help improve their health and stay youthful. Many celebrities swear by them - the actress Jenny Seagrove, for instance, uses high-dose vitamin C supplements as a booster when she's feeling rundown, and few people could argue about her success in maintaining a healthy glow.

Yet a new study has cast doubt on the benefits of these wonder pills, showing that, far from helping us, some vitamin tablets may be killing us prematurely. The study, carried out at Copenhagen University, looked at the effects of certain antioxidants (vitamins A and E, beta-carotene, vitamin C and selenium) on 250,000 patients and found that some of these compounds could harm some people, potentially causing a 5% increased risk of premature death in those who took them compared with those who did not.

The study, published in the Journal of the American Medical Association, examined the results of 68 trials on antioxidant vitamins, which are claimed to mop up free radicals, the disease-causing compounds in the body. It found that while vitamin C and selenium did not increase the risk of death, vitamins A, E and beta carotene may damage the natural defence mechanisms in some people and could lead to early death.

The vitamin supplement industry in Britain is currently worth more than £300m a year, with the most popular vitamin being C. Millions of Britons take this in the belief that in high doses it will prevent or cure a cold, which was a theory first put forward in the 1970s by Nobel-prize winning chemist Linus Pauling. Though his work was controversial, it helped kick-start the development of the vitamin-therapy industry.

Antioxidant vitamins are among the most popular supplements and are promoted by the health food industry as a way to protect ourselves from the detrimental effects of modern living: stress, pollution and pesticides. While there is anecdotal evidence to show that some people benefit from certain supplements geared at particular health conditions, some health experts have been claiming for some time that taking any vitamin in high doses regularly can be harmful. The British Nutrition Foundation says that taking too much vitamin A, for example, can make bones more brittle in old age. Some experts go as far as to say that we should bin all of our vitamin supplements.

"I'd abolish the entire vitamin supplement business, aside from giving supplements to people who are deficient or at risk of deficiency," says Mike Lean, professor of human nutrition at Glasgow University. "When you have a new medicine, there is extensive training for safety and efficacy - only then are you allowed to see if it works in general practice. If you're going to propose that a supplement is beneficial for health, it should go through the same process. This industry's claims are not based on evidence, and indeed there is evidence that says some products could be dangerous."

THE reason for this, he says, is that our bodies aren't built to handle them. "We were not designed to take mega doses of vitamins or anything else. If you take large doses of many things it will do you damage, even water. There are some vitamins you can't overdose on, like (water-soluble) vitamin C. If you take too much it just comes out in the urine, whereas fat-soluble ones such as E and A are more likely to cause problems as they accumulate in the body.

"The problem is in taking large doses in isolation. When you eat food that contains vitamin E, it contains lots of other things like carbohydrates and proteins.

"It is this balance in the food that we have evolved to accommodate. If you fish out one chemical, like vitamin E, which we need in small doses, and take a huge dose of it, no wonder it can cause damage."

Lean suggests that for good health it is better to rely on a balanced diet. However, many people say they are sceptical about how fresh and nutritious their modern diet really is, which is why they're taking vitamin supplements in the first place.

Robin Wicks, manager at the Complementary Health Centre in Dunblane, who is also a natural therapist treating patients with food allergies, says: "The soil in western countries is now demineralised and we don't always follow proper biodynamic practices that give you better food. With poor water quality, pollution and use of pesticides, we need antioxidant protection. Of course, the best thing would be to get antioxidants from natural sources like cereals or nuts. Just four brazil nuts a day will provide you with adequate selenium. But again, we can't always get the quality of produce we need, unless we pay a lot for it."

Daniela Grunwald, a nutritionist and director of studies at the College of Naturopathic Medicine in Glasgow, agrees that we can't be sure about the quality of the vitamins we're getting from food today, even organic food - much of which comes from overseas. "A lot of the fruit and vegetables we get are picked while they're still green, so they're not getting the vitamins and minerals out of the soil which they would if they were left to ripen naturally on the vine, or tree," she says.

Grunwald agrees with the findings of the study, saying that fat-soluble vitamins in particular can be dangerous. "They can be harmful to pregnant women and may damage the baby. A lot of people also think that if they take more than the recommended amounts of vitamins it's doing them extra good, but that's not the case. And even if you keep to the recommended amounts, every person tolerates vitamins differently. If you are smaller, you need smaller amounts. You won't be able to absorb vitamins properly if you are ill, if your body is clogged with toxins from a poor diet or if you have poor bowel health," says Grunwald.

However, she says, if you think you need vitamins, get advice from a trained nutritionist and steer clear of cheaper synthetic types. Go for more natural, "superfood" vitamins in powdered form, made from fermented vegetables and other foods, available from health stores.

While the British Nutrition Foundation also says that obtaining vitamins from food is preferable, it concedes that a low-dose multi-vitamin supplement can help in certain circumstances. "The times of life when individuals may benefit from supplements include pregnancy, childhood and older age."

But before you go and bin all your supplements, not everyone agrees with the findings of this latest study about antioxidants. Balz Frei, director of the Linus Pauling Institute at Oregon State University, said the Danish study and the data were flawed because more than two-thirds of its research used people with heart disease and cancer, and many were smokers. "Over the years it has become clear that antioxidants don't work in disease treatment."

  • The Food Standards Agency (FDA) has information on its website about vitamins and doses. Visit www.eatwell.gov.uk.