Authors' objectives:

As the first of a 3-part report on this topic, we analyzed relevant nutrition databases to describe the intake levels of various omega-3 fatty acids in the US population. We also performed a systematic review of the literature to assess the benefits of omega-3 fatty acid supplements or fish consumption on various CVD outcomes and to assess adverse events associated with intake of omega-3 fatty acid supplements.

Authors' results and conclusions: The intake of omega-3 fatty acids in the population varies. Corrected for energy intake, men consume significantly less alpha-linolenic acid (ALA, 18:3 n-3) than women, adults more than youths, and subjects with a history of CVD less than those without CVD. Based on analyses of a single 24-hour dietary recall in NHANES III, only 25% of the US population reported any amount of daily eicosapentaenoic acid (EPA, 20:5 n-3) or docosahexaenoic acid (DHA, 22:6 n-3) intake. Eleven RCTs and 1 prospective cohort study reported outcomes on CVD populations. The largest trial reported that fish oil (EPA + DHA) reduces all cause mortality and CVD events, although fish oil has no effect on stroke. Most other studies evaluating either fish oil or ALA supplements reported similar findings. There were few trials of ALA. In the only RCT that directly compared ALA and fish oil, both treatments were efficacious in reducing CVD outcome. No significant difference was found between the 2 supplements. Twenty-two prospective cohort studies and 1 RCT reported data on general populations. Among the cohort studies there were considerable differences among the populations studied, as well as in the estimates of fish or omega-3 fatty acids consumed. 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 no significant or negative results for the CVD outcomes. A significant benefit for stroke was reported in 1 study. The single RCT which evaluated ALA in a large general population lasted only 1 year yielding no significant results. Gastrointestinal symptoms associated with fish oil or ALA supplements are the most commonly reported adverse event and may require dose reduction or discontinuation in some individuals. Clinical bleeding is a theoretical concern but this was not borne out by the evidence.

Authors' recommendations: Overall, consumption of omega-3 fatty acids from fish or from supplements of fish oil reduces all cause mortality and various CVD outcomes. The evidence for ALA supplements is sparse and inconclusive. The adverse events due to consumption of fish oil or ALA supplements appear to be minor. Many questions remain. The studies were heterogeneous with regard to the methods of estimating fish or omega-3 fatty acid intake, background diets, settings, and the methods of reporting results. Due to these reasons, the validity of applying the results of studies conducted in countries outside of the US to the US population is uncertain. The optimal quantity and type of omega-3 fatty acid, and the optimal ratio of omega-3 to omega-6 fatty acid (if such an optimal ratio exists), remain undefined. Not much data exists concerning the needs of different subpopulations. Different types of fish and the method of food preparation may have different effects. Future research needs to address these issues.

Authors' methods: Systematic review

Project Status: Completed

URL for project: http://www.ahrq.gov/clinic/tp/o3cardtp.htm

Year Published: 2004

English language abstract: An English language summary is available

Publication Type: Not Assigned

Country: United States

Organisation Name: Agency for Healthcare Research and Quality

Contact Address: Center for Outcomes and Evidence Technology Assessment Program, 540 Gaither Road, Rockville, MD 20850, USA. Tel: +1 301 427 1610; Fax: +1 301 427 1639;

Contact Name: martin.erlichman@ahrq.hhs.gov

Contact Email: martin.erlichman@ahrq.hhs.gov

Copyright: Agency for Healthcare Research and Quality (AHRQ)