I’m not the fan of supplements that I used to be, especially fish oil. Recall the recent big and well-publicized study which found that men with high blood levels of omega-3 fatty acids were more likely to develop prostate cancer. It hasn’t been the only one to suggest that omega-3s contribute to cancer, just the most recent:

Plasma Phospholipid Fatty Acids and Prostate Cancer Risk in the SELECT Trial, Journal of the National Cancer Institute, July 2013

“Conclusions: This study confirms previous reports of increased prostate cancer risk among men with high blood concentrations of [long-chain omega-3]-PUFA. 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.”

Here’s another recent study in the same vein.  It also ends with a warning about taking fish oil:

Dietary Supplementation With Lovaza And Krill Oil Shortens The Life Span Of Long-Lived F1 Mice, Age, June 2014

Lovaza/Omacor* and/or krill oil:

• Significantly shortened life span.
• Increased the number of enlarged seminal vesicles (7.1-fold).
• Significantly increased lung tumors (4.1- and 8.2-fold).
• Increased levels of blood urea nitrogen, bilirubin, triglycerides, and blood glucose.

Doses of krill oil and Lovaza consistent with those recommended for human use decreased the life span of healthy mice. In light of the current uncertainties regarding the efficacy of purified marine oils in treating human diseases, our results do not support their use to increase health or life span.

The authors say that the mice died of either heavy bleeding or lung tumors, both a result of the effects of fish oil, not any possible toxins in the fish oil.

* These are concentrated and highly purified forms of fish oil approved as drugs by the FDA for treatment of hyperlipidemia.