Epidemiology

Antioxidant supplements do not prevent GI cancers

Last Updated: 2004-09-30 18:30:03 -0400 (Reuters Health)

NEW YORK (Reuters Health) - Findings from a meta-analysis of trial data indicate that antioxidant supplements offer no protection against gastrointestinal (GI) cancers. In fact, use of such supplements was actually tied to an increase in overall mortality. The one possible exception was selenium, but further research with better methodology is needed to verify the anti-cancer effect seen, the investigators note.

Several reports have implicated oxidative stress in the pathogenesis of cancer. However, it has been unclear if regular use of antioxidant supplements provides protection against GI malignancies.

To investigate, Dr. Goran Bjelakovic, from the University of Nis in Serbia and Montenegro, and colleagues conducted a pooled analysis of data from 14 randomized trials that compared antioxidant supplements with placebo in their ability to prevent GI cancers. A total of 170,525 patients were included in the analysis.

The researchers' findings appear in the October 2nd issue of The Lancet.

There was no evidence that use of supplements containing beta-carotene, vitamins A, C, E, or selenium, alone or in combination, protected against esophageal, stomach, colorectal, pancreatic, or liver cancer. Selenium use may have had a beneficial effect on cancer risk, but this was only observed in four trials, three of which had unclear or inadequate methodology.

In seven trials, use of antioxidant supplements was tied to an increase in mortality. In particular, beta-carotene combined with vitamin A or E significantly increased mortality.

In a related editorial, Dr. David Forman, from the University of Leeds in the UK, and Dr. Douglas Altman, from the Centre for Statistic in Medicine in Oxford, UK, urge caution in interpreting the mortality results, noting that the researchers' analysis is a "work in progress, and does not offer convincing proof of hazard."

Lancet 2004;364:1193-1194,1219-1228.