A study published in the Journal of the National Cancer Institute in 2013 reports a link between omega-3 fatty fish oil supplements and higher rates of prostate cancer among men. However, Dr. Andrew Weil and Dr. Mark Hyman both note flaws in the study, including reliance on secondary data.
Dr. Weil noted in his 2013 response to the study that omega-3 fatty acids provide numerous physical and mental health benefits to people who take them regularly. He suggested that the published study used questionable scientific methods and offered unwarranted conclusions. Dr. Hyman stated that correlation is not causation. He pointed out that the study showed a correlation between prostate cancer and men who take fish oils, but the study didn't prove a cause-and-effect relationship.