Omega-3 fatty acids are a form of polyunsaturated fat important to overall health. As it pertains to heart disease, their main benefit is their ability to reduce the risk of heart rhythm problems in certain groups of people, thus reducing the risk of sudden cardiac death. In addition, omega-3s may help reduce triglycerides, lower blood pressure slightly and reduce blood clotting.
The best source of omega-3s is fatty, cold water fish such as herring, mackerel, salmon and tuna. Plant oils, such as canola and flaxseed oils, also are sources of omega-3s.
For heart disease prevention, near-maximum benefit comes from eating two 3-ounce servings of cold water fish a week. More than that doesn't appear to offer any additional preventive benefit.
Higher amounts of two kinds of omega-3, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), may benefit some people with established heart disease or high triglyceride levels and can have an anti-inflammatory effect for people with rheumatoid arthritis. In addition, DHA is being studied to see if it can slow the progression of Alzheimer's disease.
For those who don't eat fish, a fish oil supplement or an algae supplement can provide omega-3 fatty acids. However, supplements aren't cheap, and the amount of DHA and EPA in supplements varies widely. Except for people who have established heart disease, the evidence of heart disease prevention is stronger when one eats fish instead of taking supplements. Supplements can pose risks, too.
Taking more than 3 grams of fish oil a day may increase the risk of bleeding, worsen heart rhythm problems in those who have arrhythmias or cause other side effects.