Transcript: Omega 3s, Prostate Cancer, and Atrial Fibrillation
2013 was a bad year for fish oil. Claims were crushed that the long chain omega-3s in fish oil, EPA, and DHA would stop the progression of heart disease. And then, DHA was associated with increased risk of prostate cancer and monumentally failed to treat macular degeneration. This over-the-top rhetoric sounded a little suspicious, and indeed, the paper was retracted because the author sells some rival supplement that he failed to disclose. But, he does have a point.
I covered the fish oil failure for heart disease. What about the increased cancer risk? Men with the highest circulating levels in their blood of the long chain omega-3 fat DHA were found to be at higher risk for prostate cancer. Though, a subsequent compilation of all such studies suggested EPA, the other major long chain omega-3 in fish and fish oil, may be more closely associated with increased cancer risk. Either way, these long chain omega-3s have been promoted for prevention of heart disease and cancer.
But now, we know that not only does there appear to be no benefit for death, heart attack, or stroke, but there may be an elevation in cancer risk. The general recommendations to increase the intake of these fats should consider its potential risks.
How could eating more fish or fish oil increase cancer risk? Well, there are some industrial pollutants, like PCBs, linked to increased prostate cancer risk, and the primary source of exposure in the general population is believed to be through diet: from fish, meat, and dairy products. If you do a supermarket survey, the PCBs, shown in white here, are highest in freshwater fish, and lowest in vegans—cannibals take note! No, that’s just how they label the market basket of plant foods, though vegans have been tested, and they were found to be significantly less polluted, including the PCB linked to prostate cancer.
But, this study was done in North America where people don’t eat a lot of fish. And indeed, even the group with the highest DHA levels weren’t that high. And so, maybe the confounding factor was meat consumption in general, not just fish. And, lower meat consumption may be a reason for the lower rates of prostate cancer in the lower DHA group, as the consumption of well-done meat is associated with an increased risk of prostate cancer, and intake should be restricted.
We also used to think omega-3s could protect us from arrhythmias (abnormal heart rhythms), like atrial fibrillation. Millions suffer from the condition, which causes an irregular heartbeat and a higher risk of stroke and death, but fish and fish oil consumption does not appear effective for preventing it or treating it.
Other arrhythmias can be life-threatening and cause sudden death. Despite initial encouraging results, in more recent studies, fish and fish oil consumption have not only failed to reduce sudden cardiac death with omega-3s, but actually increased mortality in cardiac patients. For example, men with heart disease, advised to eat more oily fish, or supplied with fish oil capsules, were found to have a higher risk of cardiac death—maybe because of the contaminants in fish, such as mercury?
In either case, given the inconsistent benefits and the potential adverse effects, omega-3s must be prescribed with caution, and generalized recommendations to increase fish intake or to take fish oil capsules need to be reconsidered.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.
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