Questions about fish oil: Study links Omega-3s to prostate cancer

September 3, 2013 | by Tami Dennis

The long-chain omega-3 fatty acids found in fish oil have so many health benefits and so few side effects that a daily dose has seemed like a no-brainer. Until now.


Fish oil has now been linked to a significantly higher risk of prostate cancer. One expert calls the findings a "game-changer." Fish oil has now been linked to a significantly higher risk of prostate cancer. One expert calls the findings a "game-changer."


Long linked to heart health, Omega-3s have been shown to lower high triglycerides and, at the right dosages, to reduce the risk of heart disease. Though the evidence of their benefits is less conclusive for other health conditions, Omega-3s in the form of fish oil are sometimes used in attempts to reduce the effects of rheumatoid arthritis, menstrual pain, artherosclerosis, kidney problems and age-related eye disease, to name just a few.

Now a new study has linked the consumption of these Omega-3s to a significantly increased risk of prostate cancer. For men who take the supplements to protect their heart, this study could well be “a game changer,” says City of Hope’s Cy Stein, M.D., the Arthur & Rosalie Kaplan Chair in Medical Oncology.

For the study, researchers analyzed data from a larger trial of selenium and vitamin e, known as the SELECT trial, focusing their analysis on 834 men diagnosed with prostate cancer and 1,393 randomly chosen men who didn’t have prostate cancer. The researchers then assessed the blood levels of three types of Omega-3s – EPA, DPA and DHA. They found that, compared to men who consumed the least fish oil, those who consumed the highest amounts had a 71 percent higher risk of developing high-grade prostate cancer and a 44 percent increased risk of developing any type of prostate cancer.

“A 70 percent increased risk in high-grade prostate cancer, given it’s the No. 1 cancer in men and fish is a commonly consumed thing and is thought to be a healthy food, I think it’d be a concern for people,” the study’s lead author, Theodore Brasky, said in an interview with NBCNews.

Previous studies had suggested such a connection, but the latest research – published in the Journal of the National Cancer Institute – seems fairly clear on the potential risks of consuming fish oil.

As the researchers themselves wrote: “Whereas a lack of coherent mechanisms has led authors of previous studies, including us, to consider these findings suspect, their replication here strongly suggests that long-chain Omega-3 polyunsaturated fatty acids do play a role in enhancing prostate tumorigeneis.”

Brasky, a research assistant professor at Ohio State University Comprehensive Cancer Center, speculated in an interview with HealthDay that Omega-3s may cause oxidative stress. Such stress, which damages DNA, has been linked to other cancers, he said. Brasky was at Fred Hutchinson Cancer Research Center when the study was conducted.

But the true connection is unknown. And, as Brasky points out, the study didn’t focus on fish oil’s effect on men who have prostate cancer. Some studies have suggested that, for those men, fish oil may be beneficial.

Ultimately, said City of Hope’s Stein, an expert in prostate cancer, the latest message is a familiar one: More research is needed.

Join our Prostate Cancer TweetChat on Thursday, Sept. 5 at 11 am. Follow #ProstateChat to participate.Have questions about prostate cancer? Join our TweetChat.

Cy Stein, M.D., Ph.D., and Mark Kawachi, M.D., associate clinical professor in City of Hope's Division of Urology and Urologic Oncology, will be participating in a TweetChat on Thursday, Sept. 5, from 11 a.m. to noon Pacific. They'll be discussing prostate cancer research, screening, treatment and management of possible side effects such as incontinence and impotence. To participate, follow the hashtag #ProstateChat on Twitter during that time.

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