Over the past 20 years, there has been a dramatic increase in the scientific scrutiny of and public interest in omega-3 and omega- 6 fatty acids and their impact on personal health. Omega-3 fatty acids possess anti-inflammatory, antiarrhythmic, and antithrombotic properties; omega-6 fatty acids are proinflammatory and prothrombotic. Increased consumption of vegetable oils high in omega-6 fatty acids (such as corn, safflower, sunflower, and cottonseed oils) and meats from animals that were fed grains high in omega-6 fatty acids has drastically shifted the dietary ratio of omega-6 to omega-3 fatty acids from an estimated 1:1 in the early human diet to approximately 10:1 in the typical modern American diet.
Fish and fish oil are rich sources of omega- 3 fatty acids, specifically eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are present in fatty fish and algae. Alpha-linolenic acid (ALA) is an omega-3 fatty acid present in seeds and oils, green leafy vegetables, and nuts and beans (such as walnuts and soybeans). Linoleic acid, an omega-6 fatty acid, is present in grains, meats, and the seeds of most plants. While omega-3 fatty acids have been used for treatment of many conditions, this article discusses only the most common and well-researched treatment uses.
Uses and efficacy
Cardiac mortality, sudden death, and all-cause mortality
The Diet and Reinfarction Trial (DART) was one of the first studies to investigate a relationship between dietary intake of omega-3 fatty acids and secondary prevention of myocardial infarction. In this study, 1,015 men were advised to eat at least two servings of fatty fish per week, and 1,018 men were not so advised. At the two-year follow-up, the men who had been advised to consume fish had a 29 per cent reduction in all-cause mortality but no reduction in the incidence of myocardial infarction. Sudden death caused by sustained ventricular arrhythmias accounts for 50 to 60 per cent of all deaths in persons with coronary heart disease (CHD). To date, the largest, prospective, randomised controlled trial on the effects of omega-3 fatty acids is the GISSI-Prevenzione Trial. The study included 11,324 patients with known CHD who were randomised to receive either 300 mg of vitamin E, 850 mg of omega-3 fatty acids, both, or neither. After three and one half years, the group given omega-3 fatty acids alone had a 45 per cent reduction in sudden death and a 20 per cent reduction in all-cause mortality. A meta-analysis of 11 randomised controlled trials conducted between 1966 and 1999 and including 7,951 patients with heart disease found that dietary and non-dietary fatty acids reduced overall mortality, mortality caused by myocardial infarction, and sudden death. The number needed to treat in patients at low risk to prevent one premature death was 250 for one and one-half years, and 24 patients at high risk to prevent one death. The U.S. Physicians’ Health Study surveyed roughly 20,000 male physicians and found no apparent association between fish consumption or supplementation with omega-3 fatty acids and risk for myocardial infarction, non sudden cardiac death, or total cardiovascular mortality. However, men who consumed fish at least once per week had a 50 per cent reduction in the risk for sudden death and a significant reduction in all-cause mortality.
A reanalysis of the U.S. Physicians’ Health Study found a significant inverse relationship between blood levels of omega-3 fatty acids and the risk of sudden death in men with no history of CHD.
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