Consuming omega-3 fatty acids - touted for their anti-inflammatory properties - from fatty fish or fish-oil supplements may up the risk of high-grade prostate cancer by 71 per cent, scientists have found.
The findings, by Fred Hutchinson Cancer Research Center in US, indicate that high concentrations of EPA, DPA and DHA - the three anti-inflammatory and metabolically related fatty acids derived from fatty fish and fish-oil supplements - are associated with a 71 per cent increased risk of high-grade prostate cancer.
The study also found a 44 per cent increase in the risk of low-grade prostate cancer and an overall 43 per cent increase in risk for all prostate cancers.
The findings confirm a 2011 study published by the same Fred Hutch scientific team that reported a similar link between high blood concentrations of DHA and a more than doubling of the risk for developing high-grade prostate cancer. The latest study also confirms results from a large European study.
"The consistency of these findings suggests that these fatty acids are involved in prostate tumorigenesis and recommendations to increase long-chain omega-3 fatty acid intake, in particular through supplementation, should consider its potential risks," the authors wrote in the Journal of the National Cancer Institute.
"We've shown once again that use of nutritional supplements may be harmful," said Alan Kristal, the paper's senior author and member of the Fred Hutch Public Health Sciences Division.
"What's important is that we have been able to replicate our findings from 2011 and we have confirmed that marine omega-3 fatty acids play a role in prostate cancer occurrence," said corresponding author Theodore Brasky.
Kristal said the findings in both Fred Hutch studies were surprising because omega-3 fatty acids are believed to have a host of positive health effects based on their anti-inflammatory properties.
It is unclear from this study why high levels of omega-3 fatty acids would increase prostate cancer risk, according to the authors, however the replication of this finding in two large studies indicates the need for further research into possible mechanisms, researchers said.
The difference in blood concentrations of omega-3 fatty acids between the lowest and highest risk groups was about 2.5 percentage points (3.2 per cent vs. 5.7 per cent), which is somewhat larger than the effect of eating salmon twice a week, Kristal said.
The study consisted of 834 men who had been diagnosed with incident, primary prostate cancers (156 were high-grade cancer) along with a comparison group of 1,393 men selected randomly from the 35,500 participants in the Selenium and Vitamin E Cancer Prevention Trial (SELECT).
