Research shows that consuming omega-3 fatty acids through diet is more beneficial than getting it from supplements. But if you do opt for supplements, are they safe? Here's what the studies suggest.
Contaminants. Analyses of fish oil supplements have generally not found detectable or significant levels of mercury or unsafe levels of PCBs, dioxins or other contaminants. This is not surprising, since mercury tends to accumulate in larger fish, and supplements are generally made from smaller species or algae. Moreover, the mercury in fish is water-soluble and thus tends to accumulate in muscle tissue (meat), not in the fat or oil. While most supplements are processed to reduce levels of PCBs and other contaminants, testing by ConsumerLab.com in 2012 did find that two out of 35 omega-3 supplements exceeded PCB limits.
Bleeding. Contrary to previous thinking, fish oil does not cause excessive bleeding, even when combined with blood-thinning drugs. An interaction with anti-clotting medication (such as warfarin) is theoretically possible, but recent research has found no evidence of significant risk, even at high doses. People taking anti-clotting drugs should be monitored as usual by their doctors. Similarly, you need not worry about interactions with aspirin. Indeed, the American Heart Association (AHA) advises low-dose aspirin and omega-3s for people with heart disease.
Blood sugar and cholesterol. Despite earlier concerns that fish oil supplements can raise blood sugar, a Tufts review found that the doses used in most studies have little or no effect on blood sugar control. And two studies in the American Journal of Clinical Nutrition in 2011 found that people with the highest dietary intakes or blood levels of omega-3s have a reduced risk of developing diabetes. Still, the AHA advises that taking more than three grams of omega-3 supplements daily may worsen glucose control in people with diabetes. The Tufts analysis concluded that while fish oil does not affect total cholesterol, it tends to slightly increase both LDL (“bad”) and HDL (“good”) cholesterol—but that this is unlikely to affect cardiovascular risk.
Gastrointestinal distress. In some people, fish oil supplements cause belching, a fishy aftertaste, heartburn or diarrhea.