According to a double-blind, placebo controlled study appearing in the Journal of Nutrition (2007 Apr;137(4):973-8), a small amount of DHA (docosahexaenoic acid) can moderately reduce blood pressure. The 38 male subjects were randomized to receive either 700 mcg of DHA or a placebo each day of the three month study. The study paused for four months and the role of the subjects were reversed, with the original placebo group receiving the supplement and the original supplement group receiving the placebo. Overall, subjects taking DHA had a diastolic blood pressure that was lower by 3.3 mm Hg. Heart rate was also lower in the DHA group, by 2.1 beats per minute.

 Blood pressure measuring on blue backgroundA cross-sectional epidemiological study appearing in the journal, Hypertension (2007;50:313-319) looked at blood pressure in relationship to 4,680 subjects. Blood pressure was measured eight times over four doctor visits. The researchers found an inverse relationship between omega-3 fatty acid consumption from food.

A meta-analysis of studies relating fish-oil consumption to blood pressure appeared in the Archives of Internal Medicine (June 28, 1993;153:1429-1438). In 11 studies, it was found that omega-3 fatty acids reduced blood pressure in people with normal blood pressure. Another six studies found that omega-3 fatty acids reduced blood pressure in hypertensive individuals. The greatest blood pressure reduction was in individuals with the highest blood pressure.