The effects of omega-3 polyunsaturated fatty acids on blood pressure: a methodologic analysis of the evidence.

The potentially beneficial blood pressure (BP)-lowering effects of marine omega-3 polyunsaturated fatty acids (omega-3-PUFAs) remain controversial. The objective of this qualitative and quantitative (meta-analysis) analysis was to evaluate the results of all available randomized controlled trials that studied the effect of omega-3-PUFAs on BP response. A comprehensive search of the English literature from 1970 to 1988 disclosed only six randomized controlled investigations out of 22 published reports. Four of these were evaluable and therefore eligible for this analysis. Of these, only one evaluated hypertensive subjects. In two trials, there were statistically significant reductions in BP; the one reporting an investigation of hypertensive subjects showed the greatest reduction. Using established methodologic criteria, the quality of each report was evaluated by independent observers. Following this appraisal, the outcomes of each investigation were reanalyzed and pooled using a meta-analysis. There was no statistically significant difference between the omega-3-PUFA groups and the control groups, possibly because of failure to include hypertensive subjects in all but one trial. Despite the positive effects in two studies, little scientifically valid evidence is available to demonstrate a significant BP-lowering effect of omega-3-PUFAs. Areas needing more attention in future research are identified and methods to improve study designs are suggested.