LONDON (Reuters) - Millions of people take them to
stay healthy but scientists said on Friday that vitamin supplements do not
protect against stomach and other cancers -- and may even make them worse.
An analysis of 14 trials of vitamins, or antioxidant, supplements involving
more than 170,000 people showed no benefit against cancer of the stomach,
esophagus, large bowel and pancreas. "Antioxidant supplements do not have any
influence on the incidence of gastro-intestinal cancers. On the contrary, they
seem to increase overall mortality," Dr Goran Bjelakovic, of the University of
Nis in Serbia and Montenegro, said in a telephone interview.
In a few trials included in the analysis published in The Lancet medical
journal, selenium seemed to have a protective effect against liver cancer.
But Bjelakovic said the quality of the data was poor and more trials were
needed to test the mineral's potential as a cancer preventive. "The overall
effect of all antioxidant supplements was not beneficial," Bjelakovic added.
MULTI-BILLION DOLLAR INDUSTRY
But Annette Dickinson, president of the Council for Responsible Nutrition
(CRN), a U.S.-based trade group that represents companies in the dietary
supplement industry, said clinical trials in high risk people do not really test
the hypothesis that a diet, including supplements, rich in antioxidants is
protective against cancer.
"The antioxidant story is not yet fully known and The Lancet's apparent
effort to close the chapter is premature," she added in a statement.
Antioxidants are molecules that work to reduce the damage done to cells and
DNA by free radicals -- charged chemical particles found in the environment and
produced by processes in the body.
Vitamins A, E, C and beta-carotene, a pre-cursor to vitamin A, and the trace
mineral selenium are antioxidants.
Fruits and vegetables are good sources of antioxidants. The highest
concentrations are found in spinach, carrots, red bell peppers and tomatoes.
Antioxidant supplements are a multi-billion dollar industry.
Some observational studies have suggested that antioxidant supplements could
protect against some cancers, heart disease, stroke and aging. But randomized
control trials comparing the supplements to a placebo have not backed them up.
"Antioxidant supplements are not having a good press," David Forman and
Douglas Altman, of the University of Leeds in England, said in a commentary on
the research in the journal.
They added that earlier trials to study prevention of lung cancer showed that
beta-carotene raised the risk of disease. Another trial of patients with a high
risk of cardiovascular disease showed no benefit after 5 years of treatment with
a supplement combination.
"The prospect that vitamin pills may not only do no good but also kill their
consumers is a scary speculation given the vast quantities that are used in
certain communities," they said.
