Followers of trendy health programmes that involve high doses of vitamins and minerals are allowing themselves to be used as unwitting 'guinea pigs', according to British researchers.
No one knows what adverse long term effects there might be from taking supplements at the levels promoted by some alternative therapists and celebrities, warned dietician Catherine Collins.
The mainly affluent middle-class professionals who turned to vitamins and minerals in search of 'nutrition nirvana' were putting themselves at risk, she said.
"A lot of these people who follow the example of actresses and models and do not eat very much food will be taking supplements to avoid constipation, or because they think they're good for their skin," said Collins, chief dietician at St George's Hospital, south London, and spokeswoman for the British Dietetic Association.
"They are paranoid about disease and see anything that optimises health as being good, but they are fooling themselves.
"This idea that supplements are safe to use is unproven - they haven`t been around for long enough.
"People taking high dose supplements are the guinea pigs of the future. There's no way you can record adverse effects for high levels of supplements, and absence of reported effects does not mean there's an absence of effects."
Collins also hit out at therapists and lifestyle gurus such as Cherie Blair's mentor Carole Caplin and Dr Gillian McKeith.
She accused them, and some supplement manufacturers, of taking advantage of people`s health fears and pre-occupation with diet.
"Programmes like those promoted by Gillian McKeith I think exploit the fascination we have with food," said Collins, speaking at a science briefing in London.
Dieticians were becoming concerned by the way vitamins and mineral supplements had moved into the realm of 'pseudo-medicine'.
"People are using vitamins and minerals no longer as an adjunct to diet, but as medicines in their own right," added Collins.
She saw nothing wrong with people taking a low-dose one-a-day multivitamin and mineral supplement.
There was evidence that people taking low dose supplements had reduced rates of chronic disease.
"It certainly doesn't do any harm, and could well do you some good," she said.
However taking doses many times the recommended daily allowance (RDA) could be seriously harmful.
Collins said she saw four or five people a year whose health was affected by high levels of supplements, and at least one a week who was taking an "inappropriate" dose of vitamins or minerals.
She gave the example of a woman admitted to hospital after collapsing at a bus stop who was suffering from severe unexplained diarrhoea.
Extensive investigations failed to find what was wrong with her. Then it was discovered she had been taking 3.5 gm of vitamin C and 1.5 gm of magnesium each day on the advice of a homeopath.
The recommended daily allowance (RDA) for vitamin C is 60mg and for magnesium 300mg.
"As soon as the supplements stopped, so did the diarrhoea," said Collins.
Vitamin A was one supplement commonly taken in excessive amounts, she said.
The RDA for vitamin A is 700 micrograms. Doses over 1,000 micrograms had been associated with osteoporosis and bone fractures.
A new European Union directive banning the sale of high-dose supplements is expected to come into force in August.
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