Omega-3 fatty acid may be linked to prostate cancer risk

Issue: May 25, 2011

Docosahexaenoic acid may be linked to prostate cancer risk, according to researchers from Fred Hutchinson Cancer Research Center. Their analysis demonstrated that the risk for developing aggressive, high-grade prostate cancer was two-and-a-half-times greater in men with the highest percentages of DHA compared with those with the lowest levels of DHA.

Conversely, the study found that men with the highest blood ratios of trans-fatty acids – commonly linked to inflammation and heart disease – had a 50% reduction in the risk for high-grade prostate cancer. Omega-6 fatty acids were not linked with prostate cancer risk, and none of the fats were associated with low-grade prostate cancer risk.

The findings are published in the American Journal of Epidemiology.

"We were stunned to see these results and we spent a lot of time making sure the analyses were correct," said Theodore M. Brasky, PhD, study author and postdoctoral research fellow in the Hutchinson Center's Cancer Prevention Program, said in a press release. "Our findings turn what we know or rather what we think we know about diet, inflammation and the development of prostate cancer on its head and shine a light on the complexity of studying the association between nutrition and the risk of various chronic diseases."

Chronic inflammation is associated with an increased risk for several cancers, and omega-3 fatty acids have been found to have anti-inflammatory effects. In contrast, other fats, such as the omega-6 fats in vegetable oil and trans-fats, may promote inflammation. "We wanted to test the hypothesis that the concentrations of these fats in blood would be associated with prostate cancer risk," Brasky said. â€œSpecifically, we thought that omega-3 fatty acids would reduce and omega-6 and trans-fatty acids would increase prostate cancer risk."

The mechanisms behind the effect of omega-3 fatty acids on risk for high-grade prostate cancer are unknown. "Besides inflammation, omega-3 fats affect other biologic processes. It may be that these mechanisms play a greater role in the development of certain prostate cancers," Brasky said. "This is certainly an area that needs more research."

The study was based on data from the Prostate Cancer Prevention Trial, a nationwide randomized clinical trial that examined the efficacy of finasteride for prostate cancer prevention. The trial included nearly 19,000 men age 55 and older, but the data in this analysis came from a subset of more than 3,000 of the study participants; half of these men developed prostate cancer during the course of the study and half did not. The clinical trial used prostate biopsy to confirm the presence or absence of prostate cancer in all study participants.

The majority of study participants received omega-3s through fish consumption; very few took fish oil supplements.

"Overall, the beneficial effects of eating fish to prevent heart disease outweigh any harm related to prostate cancer risk," Brasky said. "What this study shows is the complexity of nutrition and its impact on disease risk, and that we should study such associations rigorously rather than make assumptions," Brasky said.

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