MARGOT HILL is a slim, fit and perfectly healthy 23-year-old. Yet every morning she swallows six different pills with her breakfast. “I take vitamin C and E every day,” she said. “Vitamin C boosts my immune system and E is great for hair and skin. I started taking Perfectil — a new supplement on the market — about two weeks ago.”

The financial consultant is only just getting started. She’s part of a generation of health nuts who won’t rely on five portions of fruit and vegetables a day to keep them fit.

They spend £400m a year on vitamins and they don’t just want to keep coughs and colds at bay. They want optimum performance from their brains and bodies: nutritional nirvana.

But Hill, from East Sussex, claims it is hard to tell if it is the vitamins that are making the difference. “Unless you consult a nutritionist, you don’t have any idea and you have to work it out on your own,” she said.

It’s a trend that started in the 1970s, when Britons began taking vitamin C to prevent the common cold. Thirty years on, a nation of health fanatics wants pills to intercept everything from cancer to split ends.

In recent years dietary supplements have come in and out of fashion more regularly than the miniskirt. A couple of years ago everyone was taking St John’s wort for depression and PMS; then it was kava kava to calm the nerves; the B vitamins were big a year ago; and now simply everyone’s taking omega-3 — said to boost concentration, prevent breast cancer and stave off heart attacks.

Once the preserve of health food stores and hippie outlets, supplements have gone mainstream and the biggest suppliers are now supermarkets and high street chemists.

More than 21m Britons are on supplement pills, many having lost track of what they actually do. Yet they have become a sort of health insurance policy for the modern age, despite the fact that recent studies have suggested vitamin C does little to stop you catching a cold. But taking supplements cannot do you any harm. Or can it?

A European Court judgment last week upheld a European Union ruling preventing the sale of certain vitamin and mineral supplements whose health benefits have not been proven. Officials have drawn up a “positive list” of 112 that have been verified: everything else is effectively banned. British health food retailers and nutritionists have, however, appealed for a further 500 to be added to the list and they are now under review.

Once the list has been dealt with, the EU will explore the upper limits of vitamin dosage permissible and, later still, it is expected herbal supplements will come under scrutiny. Many nutritionists are up in arms, arguing that meddling Eurocrats are limiting consumer choice. Others — mostly dieticians — say it’s time this all but unregulated area was taken into hand. Vitamins and minerals, they say, can be harmful.

Too much vitamin C, for example, can give you mouth ulcers and diarrhoea. You can get kidney stones if you overdose on calcium. Excessive iron intake can prompt digestive problems and increase the risk of bowel cancer.

The checkout girl at Boots or Holland & Barrett can hardly be expected to be au courant with all of this and neither can consumers. Yet so-called megadoses of supplements are highly popular, on the basis that our fruit and vegetables have fewer nutrients than they used to and the recommended daily allowance (RDA) of vitamins and minerals established 50 years ago is out of date.

This kind of self-medication, however, can be dangerous. Catherine Collins, chief dietician at London’s St George’s hospital, once treated a patient who had overdosed on vitamin A and suffered liver failure. The pills, manufactured in Korea, contained 10 times the recommended amount.

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