Hospitals

The Omega-3/Prostate Cancer Media Fiesta — Mistaking Correlation for Causation Puts Patients at Risk

In recent days, medical news headlines have been dominated by a new study that linked omega-3 plasma levels to an increased risk of aggressive prostate cancer.  Published in the Journal of the National Cancer Institute, results from Dr. Theodore Brasky and colleagues certainly contribute to the evidence-base for omega-3 fatty acids and prostate cancer.  Yet […]

In recent days, medical news headlines have been dominated by a new study that linked omega-3 plasma levels to an increased risk of aggressive prostate cancer.  Published in the Journal of the National Cancer Institute, results from Dr. Theodore Brasky and colleagues certainly contribute to the evidence-base for omega-3 fatty acids and prostate cancer.  Yet the study — and, perhaps more accurately, the media coverage of the study — extrapolated the findings far beyond the data themselves and failed to provide adequate perspective and context around the findings. The ramifications for patient health could be serious.

There are several critical clarifications that need to be made.  First, taken as a whole, the body of evidence on omega-3s and prostate cancer points to a neutral, if not beneficial, effect of fish oil on prostate cancer.  In fact, the same team reported in 2010 that the use of fish oil supplements was not associated with any increased risk for prostate cancer.  Second, the study did not test the question of whether giving fish oil supplements or eating more oily fish increased prostate cancer risk – it simply measured omega-3 levels in the plasma (which can also be affected by genetics and metabolism) and correlated them with incident prostate cancer up to 9 years later. The authors’ conclusion that omega-3 intake causes an increase in prostate cancer risk represents an unfortunate extrapolation far beyond their data and reflects a simple logical fallacy: correlation does not imply causation. Finally, the omega-3 levels were far lower than would expected from individuals taking omega-3 supplements. Coupled with the fact that there are no fish intake or supplement use data in this paper, there is no way to reach an evidence-based conclusion that higher omega-3 intakes increase risk for prostate cancer.

Perhaps most importantly, lost in the media swirl is the critical fact that omega-3 fatty acids are associated wtih reduced risk of cardiovascular disease — the number one killer of men and women in the United States.  After reading these alarmist headlines without adequate clinical context or medical oversight, patients might take healthcare decisions into their own hands.  A patient at increased risk for heart disease may decide to cut fish from his diet, or those with elevated triglycerides may stop taking a prescription omega-3, all in order to “reduce” his risk for prostate cancer.  But at what cost?

The risk of dying from prostate cancer vs. ischemic heart disease (IHD) is startling.  The National Vital Statistics Report for deaths in the US in males in 2010 report 28,500 deaths from prostate cancer and 207,500 deaths from IHD:  a greater than seven-fold higher rate of death for heart disease.  If one assumes (conservatively) that higher fish intake reduces risk for death from heart disease by only

10%, and (liberally) increases risk for death from prostate cancer by 50%, then the chances of dying from IHD are still nearly four and a half times higher than from prostate cancer.  Even this very crude worst-case scenario analysis suggests that the benefit of higher omega-3 intakes still outweighs the risk.

Study authors and the media alike must discipline themselves to report the findings themselves and to resist the temptation to wildly extrapolate in order to grab headlines. They need to provide a balanced context to show the nuances in science that might be lost on general audiences, and to ensure that their conclusions do not overreach their data – particularly when doing so can put patients at risk.

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