Numerous studies have concluded that fish oil consumption lowers blood pressure, but a few have found no effect and others have been inconclusive.
Researchers at the Harvard Medical School in Boston, MA, have just completed a major evaluation of the results of 31 placebo-controlled trials involving 1356 subjects. They found that fish oil supplementation (mean dose of 5.6 grams/day) lowers systolic blood pressure (first [highest] reading of blood pressure measurement) by an average of 3.4 mm Hg and diastolic pressure (second [lowest] reading) by an average of 2.0 mm Hg. The effect is highly dose-dependent with 1 gram/day of fish oil lowering systolic pressure by an average of 0.66 mm Hg and diastolic pressure by an average of 0.35 mm Hg.
Fish oil supplementation does not affect blood pressure in people with normal blood pressure, but relatively dramatic effects are seen in patients with high cholesterol levels and in patients with atherosclerosis. Both eicosapentaenoic (EPA) and docosahexaenoic acids (DHA) (the main components of fish oils) are effective in blood pressure reduction with docosahexaenoic acid being slightly superior.
The Harvard researchers conclude that supplementation with 7.7 to 9 grams/day of fish oils will reduce systolic blood pressure by 4 mm Hg and diastolic pressure by 3 mm Hg in hypertensive individuals. Blood pressure reductions may be substantially larger among patients with atherosclerosis or high cholesterol levels.
Morris, Martha Clare, et al. Does fish oil lower blood pressure? A meta-analysis of controlled trials. Circulation, Vol. 88, No. 2, August 1993, pp. 523-33