Keep on taking the tablets?

Vitamins are a multi-million pound industry, but no one knows how useful they are.

The British public spends more than pounds 250m a year on vitamin supplements. The array is overwhelming - chewable, soluble, round, square, in every colour. Earlier this year, Barbara Cartland, who pops more than 60 pills a day, launched her own brand. In 1993, Mel Gibson, who attributes his victory over the bottle to vitamin C, forked out pounds 250,000 to defend consumers' rights against US government threats to ban over-the-counter vitamins. Even Baroness Thatcher thanks vitamins for her vigour.

The industry grew by 12 per cent last year. In our snacking society, vitamin supplements feed on our health anxieties, while we feed on fast food. Yet the jury remains out on the exact role that supplements should play in modern diet.

Vitamins were first identified in 1906 as a group of otherwise chemically unrelated organic compounds with two distinct properties. First, they are essential for the body's metabolism. Second, they are not capable of being produced by the body itself: they must come from the environment. If we don't consume enough vitamins, deficiency can lead to dramatic diseases such as scurvy. But illness actually caused by vitamin deficiency is rare in Western society.

Over the years, vitamins supplements have been the source of wild claims. They have been said to prevent heart disease and cancer, and increase intelligence. The World Health Organisation recommends that we eat 400g (14oz) of fruit and vegetables a day for our normal vitamin requirements (this daily quota is twice the current UK average). So what is to stop us boosting our diet with a few pills?

"Adding vitamin supplements to a diet does not transform it from unhealthy to healthy," says Sue Dibb of the Food Commission, an independent watchdog. As she points out, in April of this year, Juice Plus, a supplement that claimed to offer the benefit of eating five to seven portions of fruit and vegetables in four capsules, was told by the Advertising Standards Authority to tone down its advertisements after complaints.

On the whole, the large vitamin manufacturers make modest claims, and insist that supplements are exactly that - supplements, not replacements. The Proprietary Association of Great Britain, which represents the vitamin and health food industry, doesn't advocate replacing healthy eating with pills: "People usually get enough vitamins from their diet. Supplements can help different sorts of people who for one reason or another don't manage to get everything they need - teenagers who eat a lot of junk food or people who are losing weight."

Still, manufacturers are keen to buy into the general health benefits that vitamins may promise. The most recent claims are based on the effect of vitamins on "free radicals", the industry's latest buzzword. Free radicals are an inescapable by-product of burning food for energy. They each contain at least one unpaired electron, and are highly volatile particles that can be a contributing factor to heart disease and cancer. Free radicals are stabilised by anti-oxidants. Some anti-oxidants are produced by the body, but most are nutrients - vitamins and minerals, particularly vitamin C, vitamin E and beta-carotene.

Two years ago, the Food Commission slammed vitamin manufacturers for poor quality control. The content of pills was often wildly divergent from packaging promises and many pills dissolved so slowly they would pass straight through the bowel. Ms Dibb even talks of super rats in the sewers, gorging on second-hand vitamins. Most manufacturers dismiss thecommission's findings, but the watchdog is lobbying the Government for vitamins to be regulated like prescription medicines.

Until the day that conclusive proof of the benefits - and dangers - of vitamin supplements is found, we are left with a mere insurance policy - for those who can afford it, a relatively cheap one, or for those who are grappling with old age or long-term illness, a policy it would seem reckless not to invest in.

Vitamins: what you should know

When enough is enough: You can overdose on certain vitamins. In 1994, the National Poisons Unit issued a warning about careless use of herbal remedies after dealing with more than 600 cases where children swallowed pills and remedies thinking they were sweets. Overdoses of vitamins A, D and B6 may cause grievous illness: too much vitamin A can damage the liver and cause blurred vision and headaches; excessive vitamin D can cause kidney stones.

When to take them: The Department of Health recommends pregnant women should take folic acid up to the 12th week of pregnancy to help prevent spinal defects in the foetus. Some women are recommended to take mineral supplements to combat osteoporosis. Smokers and alcoholics, whose habits can reduce the body's ability to absorb certain vitamins, may benefit from supplements (although Finnish research early this year found that smokers had an increased risk of lung cancer while taking vitamin E and beta-carotene, an anti-oxidant and source of vitamin A).

The elderly: If certain foods are hard to eat, particularly some hard fruits, then supplements may be needed.

Children: Providing children with vitamin supplements is a controversial subject. It hits at the crux of the balanced diet debate at a time when individuals are going through important physical developments. Some argue that the modern mother has little hope of keeping track of what her children eat, so supplements are all well and good.

Dieting: Low-fat diets may cut out certain vitamins, such as vitamin E - found in vegetable oil - or some B vitamins in meat.

How they are made: Single vitamins make up 14 per cent of the market. Vitamin C is the most popular, followed by vitamin E. Vitamin C pills are synthesised from glucose, usually derived from sugar cane. The powdered vitamin is mixed for 15 minutes with maize starch after the starch has been filtered through a fine sieve. The mix is passed through a further sieve and punched into tablets.Most modern pills are film-coated rather than sugar-coated.