Do antioxidant supplements reduce the risk of cancer and deaths related to cancer?
While some trials have suggested that antioxidants have beneficial effects, results from other trials have been negative. It has been unclear which antioxidant compounts are more beneficial (or more harmful), and how individual antioxidants affect target organs and specific patient populations. To examine these issues, Mayo researchers writing in Mayo Clinic Proceedings conducted a systematic review on the topic.
“Systematic reviews can provide reliable summaries of the research, and help understand why different studies give different results,” says Victor Montori, M.D., senior author on the study and lead for Mayo Clinic’s Knowledge and Encounter Research (KER) unit.
For the study, two authors reviewed all randomized trials on antioxidants for cancer prevention(1968-2005) and identified 12 clinical trials with a total eligible population of 104,196. The review yielded a number of interesting findings including:
- Overall, antioxidant supplementation did not reduce the risk of cancer.
- Beta carotene supplementation was actually found to increase the risk of smoking-related cancers, as well as cancer mortality, and thus should be avoided, especially by tobacco users.
- Vitamin E appeared to have no beneficial or harmful effects.
- Selenium supplementation was found to lower the risk of cancer in men (not in women), but the number of trials were few and further research is required. A large trial assessing the effect of selenium in lowering the risk of prostate cancer is currently underway.
The bottom line according to Aditya Bardia, M.D., lead author of the study, is that antioxidants do not lower the risk of cancer and beta carotene might actually increase cancer risk among smokers. Selenium might have beneficial properties, but it cannot be recommended for general use until more evidence is available.
In addition to Drs. Montori and Bardia, authors of the article include James Cerhan, M.D., Ph.D.; Amit Sood, M.D.; Paul Limburg, M.D.; and Patricia Erwin, all of Mayo Clinic; and Imad Tleyjeh, M.D., King Fahd Medical City, Riyadh, Saudi Arabia.
