Vitamin supplements promise health insurance for the fast-food generation. Yet there is no proof they work, and some may be harmful

Suppose there was a pill that prevented cancer, stopped heart disease, delayed ageing, boosted brain power, enhanced vision, and preserved libido well into old age, even into the nineties.

Imagine that as an encore it also stopped snoring, prevented colds and tooth decay, cleared up spots, aided fertility, boosted memory, and kept dementia at bay.

According to some enthusiasts, there is no need to look for such a pill, it already exists and it's on sale through pharmacies, supermarkets, corner shops, the Internet, and even a few petrol stations.

The ubiquitous vitamin pill has now become as essential a part of daily life as cornflakes and breakfast TV. It comes in all shapes and sizes and colours, and there are products aimed at children, growing teenagers, pregnant women, stressed workers, sporty types, the middle aged, the elderly, and even the dog. There are also individual vitamins, combination of vitamins, some with added vitamin C, and of course, the multivitamin.

It is estimated that each day in Britain around £1m worth of vitamins and supplements are chewed, chomped, swallowed, drunk, or even, in Geri Halliwell's case, injected.

For those who use them, they are a convenient way of getting essential vitamins they believe they may not be getting in their diet, but for the sceptics, these pills of many hues are the modern-day equivalent of the medicine man's coloured potions that also came with the promise of health and well being.

What's more, say the critics, there is little proof that some of the bottled pills have the same beneficial effect as the natural vitamins, or in some cases, any benefit at all. Research is also emerging that in some cases they may be positively harmful. Researchers have warned, for example, that far from protecting against cancer, large doses of vitamin C may actually increase the risk. Vitamin C has also been linked in separate research to DNA damage.

Vitamins are a group of chemicals that are essential for life. They provide the chemical keys, or catalysts, that allow the millions of chemical reactions throughout the body, which support and maintain life, to happen. They regulate the cells, control growth and maintain health.

Despite their importance, the human body, unlike many other animals, is not capable of making vitamins without outside help.

"There are 13 vitamins that we need, but somewhere along the evolutionary line we lost the ability to make them ourselves, and we have to get them from our diet. It's suggested that we lost the ability because vitamins were so readily available in the food we ate, we no longer needed that in-house production capability,'' says Dr Sian Astley, a specialist in vitamins and health at the Institute of Food Research.

The essential vitamins are mostly found naturally in different types of food, and diet has traditionally been the main source. But the increasing use of vitamin pills ­ a 30 per cent increase in five years ­ suggests that more people are supplementing their diets with vitamins from a bottle, not from the more traditional source.

"There is no evidence that vitamins like this work, although we get through a massive number of them, but the manufacturers would probably say there is no evidence they don't work. One study we did here found that there was no beneficial effect with supplements compared to the same natural vitamin,'' says Dr Astley.

"There are also some questions we need to answer about the use of vitamins in large doses in pill form. We know, for example, that eating food rich in beta-carotene leads to a reduced risk of heart disease and cancer. But some research suggests that large supplements of beta-carotene can result in an increase in cancer. A lot of questions are being raised about whether long-term mega dosing is a good idea.''

One of the most popular of the vitamin pills is vitamin C, yet a number of different research studies have been showing that large amounts of the vitamin may have adverse effects.

Teams at Leicester and Pennsylvania have reported that large doses of the vitamin can damage DNA, potentially increasing the risk of cancer and rheumatoid arthritis. The American study found that vitamin C is capable of triggering the production of DNA-damaging chemical agents called gentoxins. DNA mutations caused by these compounds have been found in a number of different types of tumour.

"It's possible that vitamin C isn't working in cancer prevention studies because it is causing as much damage as it is preventing, although that is really speculation at this point. What we can say is that vitamin C doesn't work when you expect it to,'' suggests Dr Ian Blair, one of the Pennsylvania researchers.

And it's the lack of evidence of effectiveness that concerns a number of other specialists too, including Dr Astley.

"I personally don't take vitamin supplements because I resent coughing up the money for something the jury is still out on about whether they work and whether they are beneficial. We know that eating vitamins as a food doesn't cause harm, and with a balanced diet, people should be able to get all the vitamins they need in that way,'' she says.

The Proprietary Association of Great Britain or PAGB, the trade association responsible for regulating manufacturers of over-the-counter medicines and food supplements, says that the latest report on vitamin C and DNA damage needs to be put into perspective.

"It should not cause concern for the many people who benefit from taking vitamin C supplements. The study was performed in vitro, and not in the body.

"Because of this, it doesn't take into account that the body naturally eliminates any unwanted toxins that may be formed from using vitamin C to perform necessary functions," says a spokesman.

The industry maintains that vitamin supplements are valuable because many people are not getting the natural vitamins they need in their diets.

Karen Kelshaw of PAGB said: "People are not eating enough nutrients in their diet. There are recommended daily amounts and below those levels you can run into trouble. Some people are not receiving all the nutrients their body requires and would benefit from regular supplementation.

"Obviously, the best way to get your nutrients is through your diet, but not everybody is able to do that. Current evidence shows that the average consumption of fruit and vegetables in the UK is only three portions per day.

"If you are not eating your five portions of fruit and vegetables per day, plus fish, whole grains and dairy products, you may not be getting the right amounts of the nutrients you need to stay healthy, and in those situations, supplements may be of benefit."