July 11th, 2013

Link to Prostate Cancer Brings More Bad News for Fish-Oil Story

Adding more confusion to an already fishy story, a new study has found a significant association between omega-3 fatty acids and the risk of prostate cancer. Although the link had been previously observed, the finding surprised the investigators, who wrote that “these findings contradict the expectation that high consumption of long-chain omega-3 fatty acids and low consumption of omega-6 fatty acids would reduce the risk of prostate cancer.”

In a report published in the Journal of the National Cancer Institute, investigators analyzed data from men who had participated in the SELECT (Selenium and Vitamin E Cancer Prevention Trial) trial. They compared 834 men who developed prostate cancer with 1,393 matched controls. When compared with men who had the lowest levels of omega-3 fatty acids, men in the highest quartile of omega-3 fatty acids were at significantly increased risk for low-grade, high-grade, and total prostate cancer:

  • low-grade: hazard ratio = 1.44, CI 1.08-1.93
  • high-grade: HR = 1.71, CI 1.00- 2.94
  • total: HR = 1.43, CI = 1.09 to 1.88

Further contributing to the counter-intuitive findings, men with higher levels of trans-fatty acids had a lower risk for high-grade prostate cancer.

The authors concluded that despite the absence of a “coherent mechanism” to explain the finding, the available data,

“…suggests that long-chain omega-3 PUFA do play a role in enhancing prostate tumorigenesis. As has been made evident from many other clinical trials of nutritional supplements and cancer risk, the associations of nutrients with chronic disease are complex and may affect diseases differently. Long-chain omega-3 PUFA have been widely promoted for prevention of heart disease and cancer. Both this study and a recent meta-analysis of clinical trials showing no effects of long-chain omega-3 PUFA supplementation on all-cause mortality, cardiac death, myocardial infarction, or stroke suggest that general recommendations to increase long-chain omega-3 PUFA intake should consider its potential risks.”

The new study, although it did not specifically look at people taking fish-oil supplements, is the latest in a series of studies that have cast doubt on the benefits of fish oils and the wisdom of taking fish-oil supplements. Last year, a large meta-analysis and systematic review in JAMA found no cardiovascular benefits with fish-oil supplements. In May, a study from Italy published in the New England Journal of Medicine also found no benefits for people taking fish-oil supplements.


4 Responses to “Link to Prostate Cancer Brings More Bad News for Fish-Oil Story”

  1. Kasim Salim, MBBS MD MRCP FRCP MRCpath FRCpath says:

    Already there is cocern of Atrial arrhythmias like AF being precipitated by high dose supplementation Long chain Omega 3 PUFA in spite of the claimed benefits of preventing sudden death from Ventricular dysarrhythmias in patients with Ischemic Heart Disease(ref. Circulation Research). The added Prostate Cancer risk should alert the public to keep away Long Chain Omega 3 PUFA as a health symbol. They need not tolerate the nasty smell of Omega 3 fortified milk in tea and the difficult to swallow giant capsules filled with this oil !!
    The compound ” Resolvin” extracted from Fish Oil or Fish meat may be useful as it may help to resolve pain and inflammation.

  2. However, in another study published this year, (Mozaffarian D, et al “Plasma phospholipid long-chain omega-3 fatty acids and total and cause-specific mortality in older adults” Ann Intern Med 2013; 158:epub.) Patients with the highest levels of omega-3 fatty acids had a 27% lower risk of death during follow-up compared with study participants who had the lowest plasma levels. Most of the mortality benefit resulted from fewer cardiovascular deaths, particularly deaths related to cardiac arrhythmias. On average, people with the highest levels of the fatty acids lived more than 2 years longer compared with people who had the lowest levels. The authors concede that findings suggest that while dietary omega-3 polyunsaturated fatty acids (PUFAs) late in life may reduce total mortality, an alternative explanation for the correlational data is that “these associations could reflect an influence on life-long dietary habits.” How to reconcile these findings?

  3. Leon Hyman, Ms M.D. says:

    Did the individuals with higher levels of omega 3 fatty acids get those levels by supplements or by eating fatty fish like salmon or herring etc? Also, is there a difference between food versus supplement acquired omega 3’s? The answers to this question could seriously affect the fish industry.

  4. Review the literature. The question regarding the association between prostate cancer and long chain omega-3 fatty acid has been asked and answered many times. The answer however seems different every time.

    In a prospective study of 28,000 smokers, there was no association between prostate cancer and omega-3 FFA however there appeared to be an association with linolenic acid and increased rates of prostate cancer which was mitigated by increased Vit E. Myristic acid was also associated with increased prostate cancer risk. Cancer Epidemiol Biomarkers Prev. 2003 Dec;12(12):1422-8.

    As a prospective study, this provides better quality evidence than most epidemiologic studies.

    Another review of epidemiologic studies found no consistent in almost all cases between omega 3 consumption and prostate cancer however there was often an association between linolenic acid and prostate cancer. Some studies did show a possible correlation between fish consumption and prostate cancer. Bull Cancer. 2005 Jul;92(7):670-84.

    This association between fish consumption and prostate cancer suggests that other elements such as mercury or agricultural toxins found in fish but not in fish oil might be responsible for the observation.

    A 14 year prospective study of 47,800 men followed for 14 years found a protective association between increased DHA and EPA and prostate cancer. Am J Clin Nutr. 2004 Jul;80(1):204-16.

    A smaller case/control study found a correlation between increased ratios of n6/n3 and prostate cancer. Nutr Res. 2011 Jan;31(1):1-8. doi: 10.1016/j.nutres.2011.01.002.

    We now have another study which demonstrates something different. We do not know if the increased DHA was from eating mercury or agricultural toxin laden fish vs fish oil. We cannot be sure from this study if we are seeing selection bias with individuals seeking care with prostate screening might be more proactive in consuming DHA.

    Under any circumstance, there is a mountain of conflicting DATA out there.

    I also recoil at the credibility that a poorly designed meta analysis of omega-3 studies is granted by these authors.