EPA and DHA, the omega-3 fatty acids found in fish oil, lower blood pressure, according to an analysis of 31 trials. The effect was dependent on the amount of omega-3 oil used, with the best results occurring in trials using unsustainably high levels: 15 grams per day—the amount often found in 50 grams of fish oil. Taking 3 grams per day of omega-3 also reported significant reductions in blood pressure. One double-blind trial reported that DHA had greater effects on blood pressure than EPA or mixed fish oil supplements.

Morris MC, Sacks F, Rosner B. Does fish oil lower blood pressure? A meta-analysis of controlled trials. Circulation 1993;88:523–33.

Does fish oil lower blood pressure? A meta-analysis of controlled trials.

ACP J Club. 1994 Jan-Feb;120 Suppl 1:8-10.

Morris MC, Sacks F, Rosner B.

Department of Epidemiology, Harvard School of Public Health.

BACKGROUND. In a meta-analysis of 31 placebo-controlled trials on 1356 subjects, we examined the effect of omega-3 fatty acids in fish oil on blood pressure by grouping studies that were similar in fish oil dose, length of treatment, health of the subjects, or study design. METHODS AND RESULTS. The mean reduction in blood pressure caused by fish oil for the 31 studies was -3.0/-1.5 mm Hg (95% confidence intervals: systolic blood pressure: -4.5, -1.5; diastolic blood pressure: -2.2, -0.8). There was a statistically significant dose-response effect when studies were grouped by omega-3 fatty acid dose: -1.3/-0.7 mm Hg at doses < or = 3 g/d, -2.9/-1.6 mm Hg at 3.3 to 7 g/d, and -8.1/-5.8 mm Hg at 15 g/d. Both eicosapentaenoic acid and docosahexaenoic acid were significantly related to blood pressure response. There was no effect on blood pressure in eight studies of "healthy" persons (mean reduction, -0.4/-0.7 mm Hg) at an overall mean dose of 4.2 g omega-3 fatty acids/d. By contrast, there was a significant effect of -3.4/-2.0 mm Hg in the group of hypertensive studies with a mean fish oil dose of 5.6 g/d and on systolic blood pressure only in six studies of hypercholesterolemic patients (-4.4/-1.1 mm Hg) with a mean dose of 4.0 g/d. A nonsignificant decrease in blood pressure was observed in four studies of patients with atherosclerotic cardiovascular disease (-6.3/-2.9 mm Hg). Variations in the length of treatment (from 3 to 24 weeks), type of placebo, and study design (crossover or parallel groups) did not appear to account for inconsistent findings among studies. CONCLUSIONS. There is a dose-response effect of fish oil on blood pressure of -0.66/-0.35 mm Hg/g omega-3 fatty acids. The hypotensive effect may be strongest in hypertensive subjects and those with clinical atherosclerotic disease or hypercholesterolemia.

PMID: 8339414 [PubMed - indexed for MEDLINE]

The effect of fish oil on blood pressure in mild hypertensive subjects: a randomized crossover trial.

Am J Clin Nutr. 1993 Jan;57(1):59-64.

Morris MC, Taylor JO, Stampfer MJ, Rosner B, Sacks FM.

Center for Research on Health and Aging, Chicago, IL 60612.

We conducted a double-blind, crossover trial with 18 healthy, untreated mildly hypertensive subjects to test the effect on blood pressure of 6 or 12 g fish oil/d (50% n-3 fatty acids) as compared with an olive oil placebo. Blood pressure was measured every 6 wk in the clinic and three times daily by subjects using a semiautomated device in their homes. Compliance was determined biochemically. No significant changes in home or clinic blood pressure measurements were noted for either dose after 6 or 12 wk of treatment. Clinic blood pressure after 12 g fish oil/d was slightly lower than after placebo treatment by -0.8/-0.4 mm Hg [95% CI: systolic blood pressure (-4.4, +2.8); diastolic blood pressure (-3.2, +2.4)]. Blood pressure changes were not correlated with compliance, baseline dietary fish consumption, or blood pressure. Moderate doses of fish oil did not have a substantial effect on blood pressure. We conclude that fish oil is not a practical treatment for mild hypertension.

PMID: 8416666 [PubMed - indexed for MEDLINE]

Blood pressure lowering effect of eicosapentaenoic acid-rich diet in normotensive, hypertensive and hyperlipemic subjects.

Experientia. 1985 Apr 15;41(4):462-4.

Singer P, Wirth M, Godicke W, Heine H.

41. Mori TA, Bao DQ, Burke V, et al. Docosahexaenoic acid but not eicosapentaenoic acid lowers ambulatory blood pressure and heart rate in humans. Hypertension 1999;34:253–60.

A mackerel diet or a herring diet in which two cans of fish fillet were consumed daily over 2 weeks within a prescribed regimen, in a crossover design, were given to 15 normotensive volunteers, 14 patients with mild essential hypertension and eight patients with type IV and V hyperlipoproteinemia (HLP). In normotensives a markedly lower systolic and diastolic blood pressure at the end of the period on the mackerel diet could be observed, whereas in hypertensive and hyperlipemic subjects only systolic blood pressure was significantly decreased. After the herring diet, which served as control, changes in blood pressure were of a minor degree.

PMID: 2985425 [PubMed - indexed for MEDLINE]

Docosahexaenoic acid but not eicosapentaenoic acid lowers ambulatory blood pressure and heart rate in humans.

Hypertension. 1999 Aug;34(2):253-60.

Mori TA, Bao DQ, Burke V, Puddey IB, Beilin LJ.

Department of Medicine, University of Western Australia, and the West Australian Heart Research Institute, Perth, Australia. tmori@cyllene.uwa.edu.au

Animal studies suggest that the 2 major omega3 fatty acids found in fish, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), may have differential effects on blood pressure (BP) and heart rate (HR). The aim of this study was to determine whether there were significant differences in the effects of purified EPA or DHA on ambulatory BP and HR in humans. In a double-blind, placebo-controlled trial of parallel design, 59 overweight, mildly hyperlipidemic men were randomized to 4 g/d of purified EPA, DHA, or olive oil (placebo) capsules and continued their usual diets for 6 weeks. Fifty-six subjects completed the study. Only DHA reduced 24-hour and daytime (awake) ambulatory BP (P<0.05). Relative to the placebo group, 24-hour BP fell 5.8/3.3 (systolic/diastolic) mm Hg and daytime BP fell 3.5/2.0 mm Hg with DHA. DHA also significantly reduced 24-hour, daytime, and nighttime (asleep) ambulatory HRs (P=0. 001). Relative to the placebo group, DHA reduced 24-hour HR by 3. 5+/-0.8 bpm, daytime HR by 3.7+/-1.2 bpm, and nighttime HR by 2. 8+/-1.2. EPA had no significant effect on ambulatory BP or HR. Supplementation with EPA increased plasma phospholipid EPA from 1. 66+/-0.07% to 9.83+/-0.06% (P<0.0001) but did not change DHA levels. Purified DHA capsules increased plasma phospholipid DHA levels from 4.00+/-0.27% to 10.93+/-0.62% (P<0.0001) and led to a small, nonsignificant increase in EPA (1.52+/-0.12% to 2.26+/-0.16%). Purified DHA but not EPA reduced ambulatory BP and HR in mildly hyperlipidemic men. The results of this study suggest that DHA is the principal omega3 fatty acid in fish and fish oils that is responsible for their BP- and HR-lowering effects in humans. These results have important implications for human nutrition and the food industry.

PMID: 10454450 [PubMed - indexed for MEDLINE]