Prostate cancer is very rare among Inuit in Greenland and Canada, who live largely on fish, as well as among Japanese men, who also eat a lot of fish. But evidence on the role of fatty fish and the omega-3 acids they contain on men’s risk of prostate cancer remains contradictory.
In theory, omega-3s might be protective, perhaps because of their anti-inflammatory properties (inflammation plays a role in many cancers). And indeed, most observational studies have linked fish intake to reduced risk of prostate cancer or improved survival rates. But some studies have found no effect, and a few studies have actually linked high blood levels of omega-3s to an increased risk of prostate cancer. Those include a headline-making study published in 2013 in the Journal of the National Cancer Institute (JNCI), which linked moderately high blood levels of omega-3s to a 44 percent elevated risk of low-grade prostate cancer and a 71 percent increased risk of high-grade cancer in men over 50.
While that study merits further research, we’re not convinced by its findings. For one thing, it used data from an older study not designed to evaluate the effect of omega-3s on prostate cancer, which can complicate the interpretation of the results. More important, there are too many inconsistencies in the totality of the research, and no apparent explanation for an increased risk. Plus, if fish increased the risk of prostate cancer, then why would its incidence be lower in countries where men eat the most fish than in countries where men eat less fish? And even if fatty fish did somehow increase the risk of prostate cancer, the cardiovascular benefits of fatty fish would almost definitely outweigh any potential harms.
The same isn’t true of omega-3 (fish oil) supplements, however. Nearly all clinical trials on supplemental omega-3s for cardiovascular disease have yielded disappointing results in recent years. And studies on other proposed benefits of the capsules (against dementia or arthritis, for instance) have been even iffier. Thus, for the supplements, there are no benefits so far to outweigh the potential harms.
Our advice: Aim for two or more servings a week of fatty fish such as salmon, and steer clear of omega-3 capsules.