I suppose it may help diffuse any relevant tensions to get the punch line out of the way: I have a prostate, and in the context of my mostly-plant diet, will continue to eat fish and take a daily omega-3 supplement (krill oil in my case). We will, as well, continue using various omega-3 supplements in varying doses for specific therapeutic purposes in my clinic.
And now, let's turn to the news. Using Google this morning, I found over 8 million Web pages addressing the combination of fish oil and prostate cancer — just shy of 600,000 blogs and over 9,000 news items. Not all of these relate directly to the recent study suggesting a link between fish oil intake and prostate cancer, but many do.
So it's pretty clear I was far from alone in my eagerness to pounce on this story and opine when such headlines as "Fish oils may raise prostate cancer risks, study confirms," embellished with images of fish oil capsules, began populating print media and cyberspace alike. I have benefited from the more insightful reactions of others, mixed up though they may be with a venting of passions.
But I think it's just as well that my wife and I had a couple of vacation days out of town in a place with negligible Internet access while this tale went through the mad, early gyrations of a fish out of water. It would be easier to get the implications of this study wrong than right, and in either direction.
The study does not prove that fish oil intake causes prostate cancer. But nor is the study dismissible rubbish, as the large crowd of fish oil proponents gathered around it with harpoons in hand would like to contend.
The study in question is observational — or at least, the relevant portion of it is — meaning no intervention was undertaken. Men were not given fish oil supplements, nor fish dinners.
Rather, blood was obtained from men at baseline as they enrolled into the study. Over time, more than 800 men developed prostate cancer. The researchers matched these men on the basis of age and race to others in the study who had not developed prostate cancer, and compared those baseline blood samples for various things, notably the levels of different kinds of phospholipid fatty acids, a metabolized form of dietary fats correlated with their intake. The authors found, and they state several times in the paper, that this was at odds with their expectations, that higher omega-3 levels were seen in the men with prostate cancer than in those without.
Because the findings were counter-intuitive, and counter to the researchers' expectations, they compared them statistically to the results of other studies that had examined the same association in a meta-analysis. This part of the paper was too vaguely described for my purposes, but indicated that an association between higher omega-3 levels and increased prostate cancer has been observed with some consistency.
Others have waded deep into the kelp already and gone after this paper's school of statistical details: differences in the strength of association between prostate cancer and DHA as opposed to EPA, for instance. HuffPost blogger Johnny Bowden does some of this himself, and cites others who have as well. I leave them to it, and you to the risk of drowning in the details accessible with Google or Bing should you choose to ply these waters further.
David Katz, M.D. is director of the Yale Prevention Research Center