A study published in 2013 found that men with high levels of omega-3 fatty acids or fish oil in their blood had a 44 percent overall higher risk for prostate cancer, according to MedlinePlus. The study was published in the Journal of the National Cancer Institute.
The study involved a large, randomized and controlled trial that assessed the impact of particular vitamins and supplements on the group's chances of developing prostate cancer. The alarming results showed that men with high levels of omega-3 fatty acids in their blood were at a 71 percent heightened risk for developing a form of aggressive prostate cancer and a 43 percent higher risk for slower-growing prostate cancer overall, according to MedlinePlus.
The study included 35,500 men and was funded in part by the National Center for Complementary and Alternative Medicine and the National Cancer Institute. The authors of the study were not able to discern if the increased incidence of prostate cancer was derived from eating herring, salmon and other fish rich in omega-3 fatty acids or from taking fish oil supplements, according to MedlinePlus. Still, the study's authors claim that their results suggest that the level of fish oil in the blood seemed to indicate that prostate cancer risks were greatly increased.