contain. For example, salmon oil naturally contains more DHA than EPA; a supplement derived from algae may only contain DHA. Krill oil contains significant amounts of both EPA and DHA. Read the labels and remember, whatever supplement you buy, it must have at least 600 mg of DHA.
Be aware that only about one-third of the oil from fish is rich in EPA and DHA. Many supplements also contain vitamin E or other antioxidants to stabilize the oils and prevent them from becoming rancid. If you choose to buy a fish oil supplement, check the label carefully to see if it recommends refrigeration to prevent spoiling.
Most brands of fish oil have been proven safe, free of detectable traces of mercury, and do not contain unsafe levels of PCBs (polychlorinated biphenyls), a toxin and pollutant believed to pose various health threats.
To avoid contaminants in an unrefined supplement, it's best to choose a fish oil supplement made from small, oily fish like anchovy, sardines, or menhaden.