News

Does a high intake of fatty fish and fish-oil supplements increase prostate cancer risk?

July 12, 2013

A new US study suggests that high blood levels of omega-3 fatty acids may increase the risk of developing aggressive prostate cancer. Experts commented that the study showed no evidence of a causal relationship. However, as there is a wealth of data supporting the health benefits of an increased intake of omega 3 fatty acids, including the prevention of prostate cancer, people should not alter their behavior based on the indications found in this study.

The analysis of case studies measured plasma omega-3 fatty acid concentrations of 834 men who had been diagnosed with incident, primary prostate cancers (156 with high-grade cancer) and compared their blood levels with those of a group of 1,393 men of the same age and race (1). The participants were selected from the 35,500-strong cohort of a previously conducted large randomized controlled trial (SELECT) (2). The study results indicated that high blood concentrations of omega-3 fatty acids were associated with a 71 percent increased risk of high-grade prostate cancer, a 44 percent increased risk of low-grade prostate cancer and an overall 43 percent increased risk of all prostate cancers. The difference in blood concentrations of omega-3 fatty acids between the lowest and highest risk groups was around 2.5 percentage points (3.2 percent vs. 5.7 percent), which is somewhat larger than the effect of eating salmon twice a week.

The researchers commented that fatty acids such as eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and docosapentaenoic acid (DPA) – found in fatty fish and fish-oil supplements – seem to be involved in tumor occurrence. The findings support those of an earlier study by the same scientists which reported a similar link between high blood concentrations of DHA and a more than doubled risk of developing high-grade prostate cancer (3). According to the researchers, the results of both studies were surprising because omega-3 fatty acids are believed to have a host of positive health effects based on their anti-inflammatory properties, potentially preventing the development and growth of many cancers. It is unclear from this study why high levels of omega-3 fatty acids might increase prostate cancer risk. There is need for further re-search into possible mechanisms.

Experts commented that the study findings do not indicate a cause and effect relationship between omega-3 fatty acids and prostate cancer. Much more conclusive data is needed before we can say that the actual cause of this correlation is the intake of oily fish or fish-oil supplements. A recent meta-analysis (4), which included 31 studies, showed just how complex this research field is: in the individual studies, high fish con-sumption was linked to a decrease in the risk of prostate cancer diagnosis, some linked it with an increase in risk and several showed no significant differences in risk at all. In the same meta-analysis, pooled data from four studies on fish consumption and death from prostate cancer found a 63 percent decrease in risk as a result of high fish consumption. 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 have current policies advising 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, the experts concluded.

References

  1. Brasky T. M. et al. Plasma phospholipid fatty acids and prostate cancer risk in the SELECT trial. J Natl Cancer Inst. Published online July 2013.
  2. Lippman S. M. et al. Effect of selenium and vitamin E on risk of prostate cancer and other cancers. JAMA. 2009; 301(1):39-51.
  3. Brasky T. M. et al. Serum phospholipid fatty acids and prostate cancer risk: results from the prostate cancer prevention trial. American Journal of Epidemiology. 2011; 173(12):1429-1439.
  4. Szymanski K. M. et al. Fish consumption and prostate cancer risk: a review and meta-analysis. Am J Clin Nutr. 2010; 92:1223-1233.