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Full Title: Health Effects of Omega-3 Fatty Acids on Cardiovascular Disease
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Objectives: To describe the reported intake levels of various omega-3 fatty acids in the United States population, and to systematically review the literature to assess the benefits of omega-3 fatty acid supplements or fish consumption on various cardiovascular disease (CVD) outcomes.
Data Sources: The Continuing Survey of Food Intakes by Individuals (CSFII) and the Third National Health and Nutrition Examination Survey (NHANES III) were analyzed for dietary intake. MEDLINE®, EMBASE, Cochrane Central Register of Controlled Trials, Biological Abstracts, and Commonwealth Agricultural Bureau databases were searched for potentially relevant studies regarding the effects of omega-3 fatty acids.
Review Methods: Studies analyzed were limited to randomized, controlled trials (RCTs) and observational studies that assessed the effects over at least 1 year of measured omega-3 fatty acid consumption on CVD outcomes or risk of CVD in the general population (persons without known CVD) and in populations at high risk due to pre-existing CVD or multiple CVD risk factors. Methodological quality was assessed for both the RCTs and prospective cohort studies.
Results: Based on analyses of a single 24-hour dietary recall (in NHANES III), only a quarter of the US population reported any amount of daily intake of fish oil components. Eleven RCTs and one prospective cohort study reported outcomes on CVD populations. The largest trial reported that fish oil reduces all-cause mortality and CVD events, although fish oil has no effect on stroke. In the only RCT that directly compared alpha-linoleic acid (ALA) and fish oil, both treatments were comparable in effectiveness in improving CVD outcome.
Twenty-two prospective cohort studies, differing considerably in the populations used and estimated omega-3 intake, and one RCT reported data on general populations. Most of the large cohort studies found fish consumption was associated with lower rates of all-cause mortality and CVD outcomes, but several studies reported either no significant or negative results for the CVD outcomes.
Conclusions: Overall, consumption of omega-3 fatty acids, whether from fish or from supplements, reduces all-cause mortality and improves various CVD outcomes. The evidence for benefit from ALA supplements is sparse and inconclusive. The adverse events due to consumption of fish oil or ALA supplements, most commonly gastrointestinal symptoms, appear to be minor. It may not be appropriate to apply the results of the non-U.S. population studies to the U.S. population. Future research needs to address optimal quantity and type of omega-3 fatty acid, ratio to omega-6 fatty acids, the effect of different fish and types of preparation, and the needs of different subpopulations.
Health Effects of Omega-3 Fatty Acids on Cardiovascular Disease
Evidence-based Practice Center: Tufts-New England Medical Center
Topic Nominator: Office of Dietary Supplements, National Institutes of Health
Current as of March 2004