A large, consistent beneficial effect of omega-3 fatty acids was found only for triglyceride levels. Little or no effect of omega-3 fatty acids was found for a variety of other cardiovascular risk factors and markers of cardiovascular disease. The benefits of omega-3 fatty acids on reducing cardiovascular disease are not well explained by the fatty acids' effects on the cardiovascular risk factors we examined. A strong, linear association was found across studies between omega-3 fatty acid intake and tissue levels.
Heterogeneity of treatment effect was common among studies across the outcomes evaluated. Given the large amount of heterogeneity across studies, many questions remain about the effect of omega-3 fatty acids in improving potential CVD risk factors and intermediate markers of CVD. Few studies addressed questions related to effect modifiers and only limited conclusions could be made regarding these factors. The optimal quantity and type of omega-3 fatty acid, ratio of dietary omega-6 to omega-3, and duration of treatment remain undefined. Future research is needed to address these issues.