Study Links Omega-3 Fatty Acids and Prostate Cancer Risk

A large and prospective study shows that a high concentration of omega-3 fatty acids is linked to a higher risk of aggressive prostate cancer. Alan Kristal, professor of epidemiology at the school of Public Health at the Fred Hutchinson Cancer Center in Seattle, and colleagues show that high concentrations of fatty acids from nutritional supplements-eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA), and docosahexaenoic acid (DHA)-was linked to an overall 43% higher relative risk of prostate cancer. The results are published in the Journal of the National Cancer Institute.

The study also showed that men with high concentrations of these fatty acids had a 44% higher risk of low-grade prostate cancer and a 71% higher risk of high-grade prostate cancer compared with men who had the low levels of these fatty acids in their blood.

"We've shown once again that use of nutritional supplements may be harmful," said Kristal in a press release.

Still, the results do not show a direct cause-and-effect relationship. More studies are needed to confirm this result.

The researchers analyzed samples and followed patients from men who were part of the Selenium and Vitamin E Cancer Prevention Trial (SELECT). Participants were randomized to selenium, vitamin E, the combination of both supplements, or to placebo to test whether these supplements reduce prostate cancer risk. The study showed that while selenium had no effect, vitamin E increased the risk of prostate cancer. More than 35,000 men in North America were randomized in the study.

For the current analysis, Kristal and colleagues analyzed 834 men who had diagnosed with primary prostate cancer (including 156 who had high-grade disease) and 1,393 men randomly selected from the SELECT study.

The study results corroborate a study published by the same authors in 2011 that showed high levels of DHA in the blood also increased the risk of high-grade prostate cancer. That analysis used samples from the Prostate Cancer Prevention Trial.

According to the authors, these two studies together demonstrate a role of omega-3 fatty acids in the occurrence of prostate cancer, but do not address whether these fatty acids have a role in progression in men already diagnosed with prostate cancer.

Another recent meta-analysis on the effect of omega-3 supplementation on cardiovascular disease was published in JAMA. While several studies showed that omega-3 supplements could prevent stroke, heart attack, and other cardiac-related death, the compiled data did not come to the same conclusion, finding that omega-3 supplements did not show a benefit.

“Whereas a lack of coherent mechanism had led the authors of previous studies, including us, to consider findings suspect, their replication here strongly suggest that long-chain omega-3 poly-unsaturated fatty acids do play a role in enhancing prostate tumorigenesis,” state the authors in the discussion of their publication.

The results are surprising as omega-3 fatty acids are known to have anti-inflammatory effects and have been thought to have positive effects on health and because inflammation has been shown to promote tumorigenesis. In fact, poly-unsaturated fatty acids have been promoted to prevent cancer and cardiovascular risks.

More research is needed to understand whether high levels of omega-3’s do indeed contribute to prostate cancer tumorigenesis and the mechanism for how this occurs.