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Dietary Omega-3 Fatty Acids: Cardioprotective or Not?



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Am Fam Physician. 1999 Sep 1;60(3):962-964.

Fish and other dietary sources of omega-3 fatty acids have been considered preventive against coronary atherosclerosis. Actual cardiovascular benefit in humans has been more difficult to demonstrate. The Diet and Reinfarction Trial (DART) showed a 29 percent reduction in overall mortality rates in survivors of a first myocardial infarction who consumed fish that was rich in omega-3 fatty acids at least twice weekly for two years. Other study results show no benefit of omega-3 fatty acids in the prevention of restenosis after percutaneous coronary angioplasty. Von Schacky and associates studied the effect of two years of consumption of foods rich in omega-3 fatty acids on the progression or regression of coronary atherosclerosis as assessed by angiography.

Patients who were hospitalized for coronary angiography were asked to participate if stenosis greater than 20 percent was noted in at least one vessel and if revascularization with percutaneous transluminal angioplasty (PCTA) or coronary bypass surgery was planned or performed in the previous six months in no more than one vessel. Patients with more severe disease and significant comorbid conditions such as diabetes or bleeding tendency were excluded. In a randomized, double-blind, stratified, single-center trial, 162 patients were assigned to receive either placebo capsules or fish oil capsules and underwent angiography at baseline and at the end of the study. All capsules contained 4 mg of alphatocopherol as an antioxidant.

Patients were seen at regular intervals, with fasting lipid levels determined before randomization and after 24 months of participation. Coronary angiography was performed initially and at 24 months. All films underwent expert evaluation. If PCTA had been performed during the six months before the study or during the study, that vessel, but not the patient, was excluded from analysis. Cardiovascular events as well as coronary bypass surgery were monitored as end points.

Coronary segments among those who had ingested 1.5 g of omega-3 fatty acids per day (the approximate equivalent of the average European diet) for two years showed significantly less progression and more regression than did coronary segments in the placebo group. Clinical cardiovascular events occurred in seven patients in the placebo group and in two patients in the fish-oil group. No adverse effects were noted in either trial group. The magnitude of the mitigation of coronary atherosclerosis progression was similar to that described with cholesterol-lowering therapy, lifestyle changes designed to reduce risk factors and vigorous exercise. Fish oil increased the low-density lipoprotein (LDL) cholesterol level, which may indicate that the beneficial action is other than LDL–cholesterol lowering.

The authors conclude that intake of approximately 1.5 g of omega-3 fatty acids daily for two years modestly mitigated the course of human coronary atherosclerosis as assessed by angiography. Fewer cardiovascular events were noted. Fish eaten twice weekly or fish oil concentrate may be a useful adjunct to other treatments for the secondary prevention of coronary heart disease.

Von Schacky C, et al. The effect of dietary ω-3 fatty acids on coronary atherosclerosis. A randomized, double-blind, placebo-controlled trial. Ann Intern Med. April 6, 1999;130:554–62.

editor's note: Although fish oil is not specifically recommended in the management of hypercholesterolemia, it may be useful in patients with severe hypertriglyceridemia when diet, exercise and gemfibrozil treatment are inadequate. The beneficial effect of omega-3 fatty acids is most noticeable in persons with triglyceride levels higher than 1,000 mg per dL (11.3 mmol per L). Modest elevations of LDL cholesterol levels may occur, which are less important in patients who are severely hypertriglyceridemic. Fish oils may also prevent thrombosis by reducing platelet aggregation and may enhance thrombolysis by increasing levels of tissue plasminogen activator. Although these observations and the described study support the role of omega-3 fish oil consumption in reducing coronary disease, clear evidence for clinically significant benefit does not yet exist. Recommending fish in the diet of patients with coronary disease is still useful, since fish is a good source of protein without the high saturated fat content of many meat products.—r.s.

 


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