The Cochrane Library has published a review of antioxidant supplements for preventing mortality in health individuals and those with various diseases. The general media (The Times) have reported the findings.
The study identified 67 trials including 232,550 participants. 21 trials were conducted in 164,439 healthy individuals and 46 trials were conducted in 68,111 participants with various diseases (including gastrointestinal, cardiovascular, neurological, ocular, dermatological, rheumatoid, renal or endocrinological diseases).
The study analysed the data in many different ways examining different supplement components (for example beta-carotene, vitamin A, vitamin C, vitamin E and selenium), trials with low risk of bias and whether the study assessed primary or secondary prevention.
Overall there was no significant difference in mortality however some analyses of vitamin A, vitamin E and beta-carotene found an increased risk of mortality. Vitamin C had no significant effect either way. Selenium appeared to reduce mortality overall but when high-bias risk and low-bias risk trials were analysed separately the effect was not significant.
The authors conclude that, "we found no convincing evidence that antioxidant supplements decrease mortality". Furthermore that state, "we cannot recommend the use of antioxidant supplements as a primary and secondary preventive measure".
Action: Clinicians should be aware of this review; the wider reporting may generate patient queries. Patients who eat a healthy diet should be advised that vitamin supplements are not usually necessary.