July 11th, 2013
Link to Prostate Cancer Brings More Bad News for Fish-Oil Story
Adding more confusion to an already fishy story, a new study has found a significant association between omega-3 fatty acids and the risk of prostate cancer. Although the link had been previously observed, the finding surprised the investigators, who wrote that “these findings contradict the expectation that high consumption of long-chain omega-3 fatty acids and low consumption of omega-6 fatty acids would reduce the risk of prostate cancer.”
In a report published in the Journal of the National Cancer Institute, investigators analyzed data from men who had participated in the SELECT (Selenium and Vitamin E Cancer Prevention Trial) trial. They compared 834 men who developed prostate cancer with 1,393 matched controls. When compared with men who had the lowest levels of omega-3 fatty acids, men in the highest quartile of omega-3 fatty acids were at significantly increased risk for low-grade, high-grade, and total prostate cancer:
- low-grade: hazard ratio = 1.44, CI 1.08-1.93
- high-grade: HR = 1.71, CI 1.00- 2.94
- total: HR = 1.43, CI = 1.09 to 1.88
Further contributing to the counter-intuitive findings, men with higher levels of trans-fatty acids had a lower risk for high-grade prostate cancer.
The authors concluded that despite the absence of a “coherent mechanism” to explain the finding, the available data,
“…suggests that long-chain omega-3 PUFA do play a role in enhancing prostate tumorigenesis. As has been made evident from many other clinical trials of nutritional supplements and cancer risk, the associations of nutrients with chronic disease are complex and may affect diseases differently. Long-chain omega-3 PUFA have been widely promoted for prevention of heart disease and cancer. Both this study and a recent meta-analysis of clinical trials showing no effects of long-chain omega-3 PUFA supplementation on all-cause mortality, cardiac death, myocardial infarction, or stroke suggest that general recommendations to increase long-chain omega-3 PUFA intake should consider its potential risks.”
The new study, although it did not specifically look at people taking fish-oil supplements, is the latest in a series of studies that have cast doubt on the benefits of fish oils and the wisdom of taking fish-oil supplements. Last year, a large meta-analysis and systematic review in JAMA found no cardiovascular benefits with fish-oil supplements. In May, a study from Italy published in the New England Journal of Medicine also found no benefits for people taking fish-oil supplements.