Benefits of Omega-3 Fatty Acids
Consumption of fish oil can help reduce deaths from heart disease, but its effects on other outcomes are inconclusive, according to evidence reports from the Agency for Healthcare Research and Quality (AHRQ). The reports are available online at www.ahrq.gov/clinic/epcindex.htm#dietsup.
An analysis of 10 randomized controlled trials (RCTs) and nine other studies addressed the effects of omega-3 fatty acids on respiratory outcomes. The AHRQ could not conclude whether omega-3 fatty acids are an efficacious adjuvant or monotherapy in improving respiratory outcomes in adults or children.
Six studies were analyzed to determine the role of omega-3 fatty acids in primary prevention of asthma. Dietary fish consumption appears to serve as primary prevention for asthma in pediatric populations. However, asthma prevalence and fish intake were significantly and positively related in studies that included Asian adolescents. Another study found no association between adult asthma onset and dietary fish intake.
In terms of cardiovascular benefits, a number of studies show that fish consumption and fish and α linolenic acid (ALA) supplementation reduces all-cause mortality and various cardiovascular outcomes, although the evidence is strongest for fish and fish oil. The effects on specific outcomes (especially myocardial infarction [MI] and stroke) are uncertain, and the optimal quantity and type of omega-3 fatty acid, and the optimal ratio of omega-3 to omega-6 fatty acid remain unknown. The most significant benefit may be in reducing sudden cardiac death. Four of six RCTs found a benefit, one found no benefit, and one found harm, although all six were thought to be poorly designed. Adverse events from fish oil and ALA supplementation appear to be minor.
Overall, strong evidence shows that fish oils have a strong, dose-dependent beneficial effect on triglyceride levels. There also is evidence of possible small beneficial effects on blood pressure and coronary artery restenosis after angioplasty, exercise capacity in patients with coronary atherosclerosis, and heart rate variability, particularly in patients with recent MI. Omega-3 fatty acids do not appear to affect total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, fasting blood sugar, or glycosylated hemoglobin levels, and they had no effect on plasma insulin levels and insulin resistance in patients with type 2 diabetes.