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, oesophagus, large bowel and pancreas. “Antioxidant supplements do not have any influence on the incidence of gastrointestinal cancers.

On the contrary, they seem to increase overall mortality,” Dr Goran Bjelakovic, of the University of Niss 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

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 ageing. But randomised 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.

SOURCE: The Lancet, October 2, 2004.