I do support my patients taking omega 3 fish oil supplementation, though I caution that there is no proof that it is effective for breast cancer prevention. In addition, no one knows what "dose" is appropriate. If you can calculate based on the supplement you have the equivalent of 1/2 serving of fish a day that is reasonable. Most supplements are mercury free, but it is always important to verify.
I had a clinical trial open a few years ago 'treating' women at high risk with fish oil supplements. It was a rather involved study requiring multiple blood tests and a procedure known as ductal lavage (where a tiny catheter is placed in the nipple to extract fluid). We couldn't get women to join the study because they thought, "Gee, I'll just take the fish oil and not go through all that riga-ma-roll!" Of course that is understandable, but the problem is the medical community cannot prove benefit to any intervention, no matter how 'low tech' like a supplement, without individuals being willing to sacrifice their time and energy for an unproven benefit. Its certainly easy to see why healthy at risk women would be less motivated than perhaps a woman with cancer.
In this study reviewed by Joi, there is one group for whom use of fish oil was associated with an increase in breast cancer risk, that is the group of women who reported having recent coronary artery disease. This is surprising as one of the main beneficial properties to fish oil is the anti-inflammatory effect, and there is substantial evidence that fish oil is protective against athero-sclerotic heart disease. Perhaps having had a heart attack leads to different inflammatory markers in the blood that the fish oil has an negative interaction with. Or that finding will not hold up with future investigation. Most importantly you must remember the nature of this study- it was a prospective survey collecting many health and dietary characteristics on healthy women without cancer which was then repeated years later and matched with the state registry for breast cancer cases. It provided reinforcement that the study I was trying to do a few years ago is really needed- we have to give fish oil in a controlled environment (with a placebo) and find a minimally invasive way to look at breast biomarkers that can serve as indicators that the fish oil is reducing inflammation or cell growth without having to wait 20 years to see who develops breast cancer and who does not.
This post sent from Tel Aviv, Israel where I am enjoying a fish oil rich diet and lots of vitamin D for a week!