The study, published July 11 in the online
Journal of the National Cancer Institute, titled,
Plasma Phospholipid Fatty Acids and Prostate Cancer Risk in the SELECT Trial, showed that men with high blood levels of the omega-3 fatty acids,
EPA, DPA and DHA, have a 71 percent increased risk of high grade prostate cancer, 44 percent increase in the risk of low-grade prostate cancer and an overall 43 percent increase for all prostate cancers.
According to the
study, the difference in blood levels of omega-3 fatty acids between the lowest and the highest-risk groups in the trial was estimated at about 2.5 percent, equivalent to eating salmon twice a week.
Salmon, trout, fresh tuna and fish oil capsules are rich in omega-3 fatty acids and are believed to have significant health benefits because of their
anti-inflammatory properties.
The implication of the study is that taking a lot of fish oil supplements, and possibly, eating plenty of oily fish, could raise tremendously the risk of aggressive prostate cancer.
According to the
authors:
... recent large prospective studies have found increased risk of prostate cancer among men with high blood concentrations of long-chain ω-3 polyunsaturated fatty acids ([LCω-3PUFA] 20:5ω3; 22:5ω3; 22:6ω3]. This case–cohort study examines associations between plasma phospholipid fatty acids and prostate cancer risk among participants in the Selenium and Vitamin E Cancer Prevention Trial... [and confirmed]... previous reports of increased prostate cancer risk among men with high blood concentrations of LCω-3PUFA. The consistency of these findings suggests that these fatty acids are involved in prostate tumorigenesis. Recommendations to increase LCω-3PUFA intake should consider its potential risks.
The study was based on data collected from 834 men previously diagnosed with primary prostate cancers, including 156 with high-grade cancer, and a group of 1, 393 selected randomly from 35,000 participants in the Selenium and Vitamin E Cancer Prevention Trial (SELECT) conducted to determine whether selenium ( an essential trace mineral) and Vitamin E reduced prostate cancer risk.
The study found that fatty acids found in vegetable oils, flaxseeds and other vegetable sources had no effect on prostate cancer risk. The SELECT study also found that selenium intake did not reduce prostate cancer risk and that Vitamin E actually increased prostate cancer risk.
The marked increase in high-grade prostate cancer risk found in men with high blood levels of omega-3 fatty acids is worrisome because high grade cancer tumors are highly malignant. According to Theodore Brasky, research assistant professor at The Ohio State University Comprehensive Cancer Center, and one of the authors of the
study: "These anti-inflammatory omega-3s were associated with a 43 percent increased risk for prostate cancer overall, and a 71 percent increased risk in aggressive prostate cancer."
The authors noted that the study confirms the findings
of a previous study (2011) that reported a link between high blood concentrations of phospholipid fatty acids (including omega-3, omega-6, and trans-fatty acids) and risk of developing high-grade prostate cancer.
According to the
authors: "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."
Alan Kristal, lead author of the study and member of the Fred Hutch Public Health Sciences Division,
said: "We've shown once again that use of nutritional supplements may be harmful."
Kristal noted that although omega-3 fatty acids have been promoted as beneficial for heart patients, results of recent studies have raised doubts about the claims that omega-3 fatty acid supplementation reduces death from heart attacks and strokes in high-risk people.
Brasky, commenting on the recent studies,
said: "These fatty acids have been promoted as a blanket anti-chronic disease fatty acid. But nutrition is more nuanced, as is disease occurrence. It's about time we stop talking about foods as good or bad and no gray area. We are getting to the point where we don't see a lot of benefit for heart disease. Some of the enthusiasm for these fats has been premature."
He added: "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. It's important to note, however, that these results do not address the question of whether omega-3's play a detrimental role in prostate cancer prognosis."
The findings will come as a shock to many and highlight the risk inherent to use of supplements. Researchers will also be struggling to make sense of the findings because the anti-inflammatory properties of omega-3 fatty acids would appear to recommend them as ideal for prevention of degenerative diseases of aging, including cancer.
The authors noted that further studies are needed to explain how and why high levels of omega-3 fatty acids should increase prostate cancer risk. But they suggested that one possible mechanism may be that omega-3 fatty acids cause oxidative stress in high doses and lead to cellular and DNA damage.
