Duffy McKay, ND at Counsel for Responsible Nutrition also wrote a good commentary (pasted below) on this study.
Statement by Duffy MacKay, N.D., vice president, scientific and regulatory affairs, CRN:
“The numerous benefits of omega-3 fatty acids from foods (like salmon and sardines) and dietary supplements are well-established for men and women in all stages of life–and this new study does not change those recommendations about the importance of this nutrient. Hundreds of studies over the past two decades have shown omega-3 fatty acids to have positive effects associated with cardiovascular health, perinatal health, inflammation, cognitive function, or cancer. Collectively, this body of research serves as the basis for numerous recommendations from respected organizations, scientific boards and healthcare practitioners that Americans get omega-3 fatty acids in their diets.
While we encourage researchers to continue to study omega-3 fatty acids with an open mind, it is counterproductive when studying nutrition for researchers to promote their study as if it were the only piece of research that counts. In this case in particular, it is especially disingenuous for the researchers to make the kinds of assertions we’ve seen in the press, given their results are in stark contrast to previous epidemiologic studies1 that not only demonstrate no correlation between omega-3 consumption through fish and/or supplementation and the risk of prostate cancer, but in many cases also showed a protective effect against prostate cancer.
Further, the researchers were quick to blame dietary supplements even though there is no evidence that anybody in this study took fish oil dietary supplements. In fact, the study demonstrates no cause and effect; it can only purport to show an association between higher plasma levels of omega-3 fatty acids and those whom the researchers advise had an increased rate of prostate cancer.
One should also consider whether this study could have simply been measuring a biomarker reflecting recent intake of fish or fish oil supplements in a group of high risk cancer patients that had been told to increase their EPA and DHA levels, as compared to a group of non-cancer patients that had not been told to consume more EPA and DHA. Plasma levels of EPA and DHA reflect very recent intake and are considered a poor biomarker of long term omega-3 intake especially when compared to red blood cell levels, which reflect medium term intake. A single fish oil dose (or hearty serving of fish at lunch) results in >100 percent increase in plasma omega-3 levels. So looking at plasma levels in healthy and sick people may only provide insight into the recent habits of these individuals.
Additionally, the study’s conclusions are also limited by the fact that the study was not designed to evaluate the question the researchers sought to confirm.
The American Heart Association, the World Health Organization (WHO), the U.S. Institute of Medicine’s Food Nutrition Board (IOM FNB) and the 2010 Dietary Guidelines all have current policies advising Americans to eat more fatty fish to get the benefits of omega-3 fish oils. It is highly unlikely this one study will change that advice. Omega-3s can also be obtained by taking one of the many supplement products on the market. For those consumers who have concerns about prostate cancer or other questions about omega-3 fatty acids, we recommend speaking with your doctor or other healthcare practitioner.”
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Terry P, Lichtenstein P, Feychting M, Ahlbom A, Wolk A. Fatty fish consumption and risk of prostate cancer. Lancet 2001; 357: 1764-6
Chavarro JE et al. A 22-y prospective study of fish intake in relation to prostate cancer incidence and mortality. Am J Clin Nutr 2008; 88: 1297-303.
Augustsson, K., et al., A prospective study of intake of fish and marine fatty acids and prostate cancer. Cancer Epidemiol Biomarkers Prev, 12(1): p. 64-7, 2003.
Szymanski KM, Wheeler DC, Mucci LA. Fish consumption and prostate cancer risk: a review and meta-analysis. Am J Clin Nutr. 2010 Nov;92(5):1223-33.
Leitzmann MF, Stampfer MJ, Michaud DS, et al. Dietary intake of n-3 and n-6 fatty acids and the risk of prostate cancer. Am J Clin Nutr. 2004 Jul;80(1):204-16.
Ritchie JM, Vial SL, Fuortes LJ, Robertson LW, Guo H, Reedy VE, Smith EM.Comparison of proposed frameworks for grouping polychlorinated biphenyl congener data applied to a case-control pilot study of prostate cancer. Environ Res. 2005 May;98(1):104-13.