Studies of fish oils and extract in the form of pills and formulas for heart disease have not been uniformly promising. The best results are for patients with a history of heart attack. In the GSSI Prevenzione Study, 11,000 Italian post heart attack patients on standard medication therapy who took 850 mg of omega-3 fatty acids (present in fish oil) each day had a 45% reduction in cardiac health (GISSI. 1999). In another study extracts of n-3 polyunsaturated fatty acids also led to a significant reduction in heart attacks in men with heart disease (Burr et al 1989). Contrary to public opinion and to what you read in the papers, however, omega-3 fatty acids will not prevent heart disease.
A recent analysis of the studies of omega-3 fatty acids looked at 41 studies with a total of 36,913 participants (Hooper et al 2006). This analysis showed no reduction in cardiovascular events or total mortality with omega-3 supplementation using fish oils and other supplements. There was a 7% increase in cancer, which was not statistically significant.
In the Study on Omega-3 Fatty Acids and Ventricular Arrhythmia (SOFA) study, 546 patients with implantable fibrillators and ventricular arrhythmias were randomized to receive 2g/day fish oil or placebo. Thirty percent of the fish oil group had their defibrillator go off or died compared to 33% of the placebo group (not a significant difference) (Brouwer et al 2006).
In addition to not helping to prevent heart disease, omega-3 fatty acids in the form of fish oil supplements may even cause harm in some heart disease patients. In the DART-2 study 3114 men with stable angina (chest pain) were randomly assigned to receive omega-3 supplements or placebo. Instead of protection from heart disease, the omega-3 group had a statistically significant increase in sudden death and cardiac death (Burr et al 2003). The excess of deaths was seen more in those taking fish oil capsules than in those eating oily fish. In another study (Leaf et al 2003) 200 patients with a history of a potentially lethal heart arrhythmia called ventricular tachycardia were given omega-3s or placebo. The supplements increased the amount of potentially lethal ventricular tachycardias.
Fish oil supplements or other food products to which omega-3 fatty acids have been added do not prevent heart disease in people without a history of heart disease and have questionable beneficial effects in people with a history of heart disease. I do not recommend taking them unless you have had a heart attack, and in that case you should confer with your doctor since they may exacerbate heart arrhythmias. You can get these effects by eating the foods like fish that contain Omega-3, and people that ate those foods in the clinical trials did better than people who took the supplements. In addition, if you take too many fish oil supplements you might end up smelling like a fish! Better to eat a 4-6 ounce serving of seafood in your diet at least twice a week).
Brouwer IA, Zock PL, Camm AJ, et al (2006): Effect of fish oil on ventricular tachyarrhythmia and death in patients with implantable cardioverter defibrillators: The study on Omega-3 fatty acids and ventricular arrhthmia (SOFA) randomized trial. Journal of the American Medical Association 295:2613-2619.
Burr ML, Ashfield-Watt PAL, Dunstan FDJ, Fehily AM, Breay P, Ashton T (2003): Lack of benefit of dietary advice to men with angina: results of a controlled trial. European Journal of Clinical Nutrition 57:193-200.
Burr ML, Fehily AM, Gilbert JF, Rogers S, Holliday RM, Sweetnam PM (1989): Effects of changes in fat, fish, and fibre intakes on death and myocardial reinfarction. Lancet 2:757-761.
GISSI. (1999): GISS-Prevenzione Investigators (Gruppo Italiano per lo Studio della Sopravvivenza Nell'Infarto Miocardio). Dietary supplementation with n-2 polyunsaturated fatty acids and vitamin E after myocardial infarction: results of the GISSI-Prevenzione Trial. Lancet 354:447-455.
Hooper L, Thompson RL, Harrison RA, et al (2006): Risks and benefits of omega 3 fats for mortality, cardiovascular disease, and cancer: systematic review. Bmj 332:752-60.
Leaf A, Kang JX, Xiao Y-F, Billman GE (2003): Clinical presentation of sudden cardiac death by n-3 polyunsaturated fatty acids and mechanism of prevention of arrhythmias by n-3 fish oils. Circulation 107:2646-2652.
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