Updated September 4, 2019
Looking for a way to protect themselves against heart attack and stroke, many men have turned to eating more oily, cold water fish—or taking fish oil supplements—to boost the amount of omega-3 fatty acids in their body. But a study links high blood levels of omega-3 fatty acids—found in fatty fish and fish oil supplements—to a 71 percent increase in aggressive prostate cancer in men.
This approach once seemed reasonable, largely due to the anti-inflammatory properties of this naturally-occurring compound, as well as previous studies that showed some benefit of omega-3 fatty acids for people who had already had a heart attack or stroke.
Study Finds Link Between Omega-3 Fatty Acids and Prostate Cancer Risk
The most recent study, published July 11 in the Journal of the National Cancer Institute, used data on over 2,200 men from a previous study to examine the link between blood levels of omega-3 fatty acids and prostate cancer.
Instead of asking men how much fish or fish oil supplements they consumed, researchers measured the blood levels of EPA, DPA and DHA, three omega-3 fatty acids found in cold water fish such as Alaskan salmon, mackerel and sardine.
Men with the highest levels of omega-3 fatty acids in their blood had a 43 percent increased risk of prostate cancer overall, compared to men with the lowest levels.
In addition, men with high omega-3 fatty acid blood levels were 71 percent more likely to develop an aggressive form of prostate cancer. This is especially important, because this type is most likely to be fatal.
The difference in the blood level of omega-3 fatty acids between men in the highest and lowest groups was about 2.5 percent. That means men in the high group would need to eat salmon two more times per week—or the equivalent in fish oil pills—than the low group to achieve this greater amount in their blood.
Foods Are Not Good Or Bad, But Gray
“These fatty acids have been promoted as a blanket anti-chronic disease fatty acid,” said the study’s lead author Theodore Brasky, PhD. “But nutrition is more nuanced, as is disease occurrence. It’s about time we stop talking about foods as good or bad and no gray area.”
While the study shows a connection between intake of omega-3 fatty acids from oily, cold water fish, it doesn’t prove that these compounds cause prostate cancer. It does, however, support two previous studies with similar results.
In addition, the study didn’t look at whether higher amounts of omega-3 fatty acids in the blood increase the risk of dying from prostate cancer.
Future research should take into account other risk factors for prostate cancer, such as family history, age and race. In addition, studies are needed in which men are assigned to take either omega-3 fatty acids or a neutral placebo pill, to see how many men develop prostate cancer from each group.
This type of randomized clinical trial was carried out by Italian researchers—published recently in the New England Journal of Medicine. In their study, they found that omega-3 fatty acids didn’t reduce the risk of death from heart disease, heart attacks or strokes in people who already had risk factors for those.
Moderation With Omega-3 Fatty Acids Is Key
Long touted for its anti-inflammatory benefits, omega-3 fatty acids have now moved into what Brasky refers to as the “gray area.”
“We’ve shown once again that use of nutritional supplements may be harmful,” said Alan Kristal, Dr.P.H., the senior author of the JNCI paper.
This, no doubt, leaves many men in nutritional limbo. Currently, the American Heart Association recommends eating oily, cold water fish at least two times a week (or two servings).
For men concerned about both their hearts and their prostate, though, the best advice—until more definitive studies are done—may be to eat oily, cold water fish or fish oil pills only in moderation, and hold off on the mega-doses unless recommended by your doctor.