Eating two servings of fatty fish a week — equal to about two grams of omega-3 fatty acids — lowered the risk of death from heart disease by more than a third and total deaths by 17 percent.
Omega-3s in fish clearly have effects that can account for such findings. They protect against abnormal heart rhythms, lower blood pressure and heart rate and improve the function of blood vessels. They may also lower heart-damaging triglycerides and counter inflammation, a known risk to the heart.
The question is whether the observed cardiovascular benefits often found among fish eaters is due solely to the oils in fish or to some other characteristics of seafood or to still other factors common to those who eat lots of fish, like eating less meat or pursuing a healthier lifestyle over all. Whatever the answer, it does not seem to be fish oil supplements.