The March 2008 issue of the "Mayo Clinic Proceedings" includes an article reviewing three decades of research examining the effects of omega-3s on preventing heart attacks. In aggregate, these studies affirm a protective effect of the type of omega-3 found in fish oil. The studies demonstrate omega-3s reduce heart attack incidents in a range of from 19 to 45 percent. The authors report that the findings suggest that intake of omega-3s, either in supplement form or from dietary sources should be increased, especially in those with or at risk of coronary disease.
Primary or Secondary Prevention
The authors caution that rigorously controlled studies examining the effects of omega-3 fatty acids in reducing the risk of a first heart attack have not yet been performed. However, there is evidence supporting a primary prevention benefit. Studies of people's diets demonstrated that those with a high omega-3 intake are at reduced risk of all types of cardiovascular diseases. One fish meal a week was associated with a 15 percent reduction in heart attack risk. Consumption of five or more fish meals per week was associated with a 40 percent decrease in risk.
Is EPA or DHA Better?
The heart-protective nutrients in omega-3 fish oil include eicosapentaenoic acid and docosahexaenoic acid -- EPA and DHA, respectively. No trials comparing EPA and DHA with heart attack prevention have been conducted. Subsequently neither can be assessed as more cardio-protective than the other; however, some studies have shown that DHA can reduce blood pressure more than EPA. Accordingly, physicians recommend patients supplement equal amounts of DHA and EPA. Most patients with heart disease find it difficult to take in recommended amounts from food sources and take supplements instead.
Dosages
The American Heart Association endorsed omega-3 fatty acids for use by people to help prevent second heart attacks, and for those at high risk. Their recommendation calls for 1 g mixture of DHA and EPA daily. While dietary sources are preferred, supplementation in capsules or liquid form is also endorsed. The Food and Drug Administration approved an omega-3 ethyl ester formulation, at a dosage of 4 g per day to treat high triglyceride levels. Target levels for people without heart disease are at least 500 mg daily.
Adverse Effects
In the placebo-controlled trials, adverse side effects occurred no more frequently than 5 percent of the time. Further, there was no difference in side effect frequency between the placebo and omega-3 fatty acid groups. The most common adverse effects were a fishy burp, gastrointestinal upset and nausea. These were largely avoided by taking the capsules at meals, bedtime or ingesting an enteric coated form. While early studies indicated high doses might prolong bleeding times, a 2007 study concluded virtually no increased bleeding risk at doses up to 7 g per day.
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