The Antihypertensive Effects of Fish Oil

Abstract

Both n–3 and n–6 polyunsaturated fats have been suggested to lower blood pressure, an effect ascribed to altered biosynthesis of eicosanoids. To test these hypotheses, we studied blood pressure and eicosanoid production during supplementation of dietary fat for four weeks in 32 men with mild essential hypertension. Supplementation was preceded and followed by four-week run-in and recovery periods. Groups of eight subjects received either 10 ml or 50 ml of fish oil (3 or 15 g of n–3 fatty acids) daily, 50 ml of safflower oil (39 g of n–6 fatty acids), or 50 ml of a mixture of oils that approximated the types of fat present in the American diet. The biosynthesis of eicosanoids was assessed by the measurement of urinary metabolites.

Blood pressure decreased in the men who received the high dose of fish oil (systolic pressure by a mean of 6.5 mm Hg [P<0.03] and diastolic pressure by 4.4 mm Hg [P<0.015]), but not in the other groups. Although the formation of vasodilatory prostacyclins (prostaglandins I₂ and I₃) increased initially, this increase was not maintained as blood pressure fell. The level of THROMBOXANE A₂ metabolites fell; metabolites of thromboxane A3 were detected in the groups receiving fish oil. The formation of prostaglandin E₂ increased during supplementation with safflower oil and tended to decrease with fish oil; no prostaglandin E₃ metabolite was detected.

Our data indicate that high doses of fish oil can reduce blood pressure in men with essential hypertension. However, the clinical usefulness and safety of fish oil in the treatment of hypertension will require further study. (N Engl J Med 1989; 320:1037–43.)