Im a bit rusty on my fish oil but the general consensus that I subscribe to is fish oil is a good thing as long as its from cold sources and not heat processed which causes the oil to become rancid which just adds to our toxic load. 3g seems to be a good starting point. I know a lot of high end athletes literally take >10g a day. Have to be careful with thinning your blood too much though.
Recently there was a study done on selenium and vit E as they relate to prostate cancer. Over the course of the study they found in the men who got prostate cancer there were elevated amounts of omega 3's. They also claimed the the selenium had no effect and vit E raised risk slightly.
The problems with so many of these nutritional studies is that first and foremost the overall health of an individual is questionable at best and secondly a complete nutritional evaluation isnt done for participants and in cases where one element may be missing from a diet, adding others may promote the bodies secondary actions that are often (inaccurately) linked to disease or make something worse.
What I mean by the above is that often times having a nutritional imbalance can have a negative effect and if that isnt considered or taken into account then it can lead to an inaccurate or at least misleading outcome.
A prime example of this is iodine and selenium. If you supplement with selenium and are iodine deficient it will just make your iodine deficiency even worse. Thyroid health does have a direct effect on prostate health so maybe the results from the study were also impacted by degrading thyroid function by adding selenium but not iodine?