A prospective study of plasma fish oil levels and incidence of myocardial infarction in U.S. male physicians

Objectives. This study evaluated whether increased intake of fish oils (eicosapentaenoic and docosahexaenoic acids) might reduce the risk of coronary heart disease. Background. Observational and clinical studies have suggested that increased intake of fish oils, as reflected in plasma levels of fish oils, may reduce the risk of myocardial infarction. Methods. A nested case-control study was conducted among the 14,916 participants in the Physicians' Health Study with a sample of plasma before randomization. Each participant with myocardial infarction occurring during the first 5 years of follow-up was matched by smoking status and age with a randomly chosen control participant who had not developed coronary heart disease. Results. Mean levels of fish oils (with 95% confidence interval [CI] for paired differences and p values) in case and control participants, expressed as present of total fatty acids, were, for eicosapentaenoic acid, 0.26 versus 0.25 (95% CI - 0.03 to 0.05, p = 0.70) in cholesterol esters and 0.56 versus 0.54 (95% CI -0.04 to 0.09, p = 0.44) in phospholipids, and for docosahexaenoic acid, 0.23 versus 0.24 (95% CI -0.07 to 0.04, p = 0.64) in cholesterol esters and 2.22 versus 2.14 (95% CI -0.10 to 0.27, p = 0.36) in phospholipids. Results adjusted for major cardiovascular risk factors showed a very similar lack of association between fish oil levels and the incidence of myocardial infarction. Conclusions. These results indicate no beneficial effect of increased fish oil consumption on the incidence of a first myocardial infarction. However, the effect of very high levels of fish oils could not be evaluated.