The omega-3 fatty acid DHA in fish oil is associated with a reduced risk of heart disease. Epidemiologists suggest men should be cautious about loading up on DHA, though. They found men getting high levels of DHA had more than double the risk of an aggressive prostate tumor. There was no impact on the more common low-grade prostate cancer. Eating fish, on the other hand, should pose no risks.
[American Journal of Epidemiology, online April 24, 2011]