There's growing concern about mercury found in certain types of fish. But there's no evidence that fish oil supplements contain mercury. Studies indicate that mercury is more likely to accumulate in the meat of the fish rather than in the oils. One recent study of 20 brands of fish oil supplements found no mercury contamination. But theoretically, it's possible that some fish oil supplements may contain mercury. If you're concerned, look for supplements that state on the label that they are free of mercury.
The American Heart Association recommends that healthy adults eat at least two servings of fish a week. Fatty fish, such as mackerel, tuna and salmon, contain omega-3 fatty acids. Studies show that omega-3 fats can help prevent heart attack and stroke. The best way to get omega-3 is from food sources. But some people may benefit from a fish oil supplement.