In July 2013 a study was published in the Journal of the National Cancer Institute linking elevated blood levels of omega-3 fatty acids to prostate cancer development. As you would expect, any such announcement would be met with both anxiety and concern. In order to discuss this in greater detail let's look into how the study was performed.
The data was gathered from the SELECT trial (2001), which originally was started to determine if selenium or vitamin E could reduce prostate cancer development; neither of which was the case. The authors of the current study used blood sample information from SELECT and compared this to the rate of prostate cancer development. They found that patients with elevated levels of omega-3 fatty acids had a 43% higher risk of developing prostate cancer, and a 71% higher chance of developing high-grade (more fatal) prostate cancer.
What is important to realize is that this study was not a randomized attempt to determine if omega-3 fatty acids increase the risk of prostate cancer. Multiple studies have been done without this being shown. Furthermore, the statistical difference between the control group and the study (fatty-acid group) was 0.2%. Whether this was meaningful in the real world is not yet known.
In addition, whether this level difference was due to use of dietary supplements was unknown as this was not asked during the study. Were these men eating more fish, using supplemental pills (and what type or dose), or is there an unknown factor?
Therefore, the story is still incomplete. Omega-3 fatty acids are essential nutrients -- meaning that we must get them from our diet as we cannot produce them. Evidence exists that they promote cardiovascular health and cognitive function and higher levels have been associated with reduced risk of death from all causes.
As a result, I recommend we promote a well-rounded diet. If you can eat without needing supplements you can likely obtain all the nutrients you need without assistance. Obviously, this is an area in need of much study which I suspect will be coming.