A weakly constructed study was reported recently that purportedly associated higher levels of omega-3 fatty acid blood levels and prostate cancer. See this CBS News report, for instance.
Lipid and omega-3 fat expert, Dr. William Harris, posted this concise critique of the study, exposing some fundamental problems:
First, the reported EPA+DHA level in the plasma phospholipids in this study was 3.62% in the no-cancer control group, 3.66% in the total cancer group, 3.67% in the low grade cancer group, and 3.74% in the high-grade group. These differences between cases and controls are very small and would have no meaning clinically as they are within the normal variation. Based on experiments in our lab, the lowest quartile would correspond to an HS-Omega-3 Index of <3.16% and the highest to an Index of >4.77%). These values are obviously low, and virtually none of the subjects was in “danger” of having an HS-Omega-3 Index of >8%. So to conclude that regular consumption of 2 oily fish meals a week or taking fish oil supplements (both of which would result in an Index above the observed range) would increase risk for prostate cancer is extrapolating beyond the data.
This study did not test the question of whether giving fish oil supplements (or eating more oily fish) increased PC risk; it looked only a blood levels of omega-3 which are determined by intake, other dietary factors, metabolism and genetics.
The authors also failed to present the fuller story taught by the literature. The same team reported in 2010 that the use of fish oil supplements was not associated with any increased risk for prostate cancer. A 2010 meta-analysis of fish consumption and prostate cancer reported a reduction in late stage or fatal cancer among cohort studies, but no overall relationship between prostate cancer and fish intake. Terry et al. in 2001 reported higher fish intake was associated with lower risk for prostate cancer incidence and death, and Leitzmann et al. in 2004 reported similar findings. Higher intakes of canned, preserved fish were reported to be associated with reduced risk for prostate cancer. Epstein et al found that a higher omega-3 fatty acid intake predicted better survival for men who already had prostate cancer, and increased fish intake was associated with a 63% reduction in risk for aggressive prostate cancer in a case-control study by Fradet et al). So there is considerable evidence actually FAVORING an increase in fish intake for prostate cancer risk reduction.
Another piece of the picture is to compare prostate cancer rates in Japan vs the US. Here is a quote from the World Foundation of Urology:
“[Prostate cancer] incidence is really high in North America and Northern Europe (e.g., 63 X 100,000 white men and 102 X 100,000 Afro-Americans in the United States), but very low in Asia (e.g., 10 X 100,000 men in Japan).”
Since the Japanese typically eat about 8x more omega-3 fatty acids than Americans do and their
blood levels are twice as high, you’d think their prostate cancer risk would be much higher…
but the opposite is the case.
Omega-3 fatty acids are physiologically necessary, normalizing multiple metabolic phenomena including augmentation of parasympathetic tone, reductions of postprandial (after-meal) lipoprotein excursions, and endothelial function. It would indeed make no sense that nutrients that are necessary for life and health exert an adverse effect such as prostate cancer at such low blood levels. (Recall that an omega-3 RBC index of 6.0% or greater is associated with reduced potential for sudden cardiac death.)
I personally take 3600 mg per day of EPA + DHA in highly-purified, non-oxidized triglyceride form (Ascenta Nutrasea liquid) that yields an RBC omega-3 index of just over 10%, the level that I believe the overwhelming bulk of data suggest is the ideal level for humans.
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