Overall, the findings "do not provide strong support for population-wide implementation of high-dose antioxidant supplementation for the prevention of prostate cancer," write the researchers. They included Richard Hayes, PhD, of the National Cancer Institute.
However, they note two possible exceptions: Men who smoke and men whose diets don't include much beta-carotene, the nutrient that makes carrots orange.
Past studies haven't settled whether or not antioxidants prevent prostate cancer, the researchers write. Their study may not be the final verdict, either.
About the Study
The researchers studied more than 29,000 men for up to eight years. When the study started, the men took surveys about the foods they ate and any supplements they took.
Of particular interest were the men's intake of the antioxidants vitamin E, vitamin C, and beta-carotene. The researchers wanted to see if consuming those antioxidants -- from food or supplements -- affected prostate cancer risk.
The surveys covered 137 foods. But nuts and vegetable oil -- prime sources of vitamin E -- were generally not captured by the survey, Kirsh's team notes. As for supplements, most don't include all forms of vitamin E.
None of the men was asked to change his diet or use of supplements. Instead, the researchers observed which men developed prostate cancer. They also adjusted for prostate cancer's known risk factors, including advanced age.
During follow-up, a total of 1,338 cases of prostate cancer were identified in the group.
Vitamin E, vitamin C, and beta-carotene consumption didn't appear to affect prostate cancer risk, the study shows. But two groups of men stood out.
Among current and recent smokers, advanced prostate cancer risk was lower in men taking vitamin E supplements. However, there was a trend for increased risk of nonadvanced cancer with increasing use of vitamin E supplements in current and recent smokers. In men with low dietary intake of beta-carotene, prostate cancer risk was lower with use of beta-carotene supplements.
The reasons for those findings aren't clear. A journal editorial calls the data on vitamin E and smoking "intriguing" but stresses that quitting smoking is a surer way to avoid cancer and many other chronic diseases.
Past studies of vitamin E and cancer have generally been "disappointing," write the editorialists, who included I-Min Lee, MBBS, ScD, of Harvard Medical School in Boston.