Last week, the Journal of the National Cancer Institute published the results of a randomized clinical trial by researchers at the University of California, Los Angeles, that found folic-acid supplements significantly increase the risk of prostate cancer. In the same issue, the Center's Dr. Alan Kristal co-authored a related editorial concluding that the data on folate supplementation and prostate cancer adds to the growing body of knowledge indicating that micronutrient supplementation does not lower cancer risk.
In "Nutritional Prevention of Cancer: New Directions for an Increasingly Complex Challenge," Kristal, a nutritional epidemiologist in the Public Health Sciences Division's Cancer Prevention Program, and co-editorialist Dr. Scott Lippman, of M.D. Anderson Cancer Center, suggest that it is time for researchers to go back to large, epidemiological studies, using improved modern methods, to look for ways in which diet—whole foods—can lower cancer risk. They also suggest that investigators should first complete small studies in humans to understand how dietary chage or supplements affect biological mechanisms related to cancer, and only then progress to large-scale randomized clincial trials.
According to a secondary analysis from the Aspirin/Folate Polyp Prevention Study (AFPP), men who took a daily folic-acid supplement had more than twice the risk of prostate cancer compared with men who took a placebo. The primary goal of the AFPP study was to determine the impact of aspirin and folate on colon polyps in men and women who were at high risk of disease. The effect of folate supplementation on prostate-cancer risk was unknown.
To learn how folate supplements might affect prostate-cancer risk, Dr. Jane Figueiredo, of the Keck School of Medicine at the University of Southern California in Los Angeles, and colleagues analyzed prostate cancer incidence among 643 men who were randomly assigned to folate or placebo in the AFPP study and who enrolled in an extended follow-up study.
The estimated prostate cancer risk was 9.7 percent at 10 years in men assigned to folate supplements, compared with 3.3 percent in men assigned to placebo; the difference was statistically significant. In contrast, baseline dietary folate intake and plasma folate showed a trend toward reduced risk of prostate cancer, although the difference did not reach statistical significance.
Editorialists Kristal and Lippman wrote, "It is safe to conclude that cancer prevention is not going to be as simple as recommending high-dose micronutrient supplements for middle-aged and older adults.
[Adapted from a Journal of the National Cancer Institute news release.]