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High doses of fish oil reduce blood pressure.


High doses of fish oils have helped reduce blood pressure in men with mild hypertension, says a team of Vanderbilt University researchers. The Nashville, Tenn., team reports they could not duplicate this effect with low doses of fish oil, safflower oil, or a mixture of oils that approximated the types of fat present in the American diet. The study also raises new questions about how the fish oils produce this effect biologically.

Thirty-two men with mildly elevated blood pressure were tested over a 12-week interval. The team reports that tests showed that high amounts of fish oil supplements produced a "magnitude of effect...similar to that of a diuretic or propanolol [a drug used to lower blood pressure]." The study was designed to measure the effects of fatty acids derived from fish oils and from polyunsaturated vegetable oils in producing prostaglandins, naturally occurring fatty acids that, among other functions, have the ability to regulate blood pressure. All of the subjects in the study were expected to undergo a four-week run-in period followed by four weeks of consuming dietary oil supplements and a four-week recovery period. The men were divided into four eight-man groups: one group received 10 ml. of fish oil daily, while another received five times that amount; one group consumed 50 ml. of safflower oil, while another consumed the same amount of a mixture of oils.

"Blood pressure decreased in the men who received the high dose of fish oil, but not in the other groups," says Dr. Howard R. Knapp of Vanderbilt's division of clinical pharmacology. Mean systolic and diastolic pressures both dipped slightly in the fish oil group, Knapp adds. It wasn't the synthesis of prostaglandins that turned out to be the cause of it all, as originally thought, however. Knapp says that although the initial formation of prostaglandins increased, this increase did not maintain itself once blood pressure levels fell. Knapp adds, however, that one potentially adverse effect of high amounts of fish oil supplements might be further problems for patients with kidney impairments, and that "further work will be needed to clarify the issue."

Overall, the study concludes that its findings" raise the possibility that dietary supplementation with marine oils or, more probably, highly enriched preparations of [fish oil derived] fatty acids m be found to have benefit in the treatment of essential hypertension." (New England Journal of Medicine, April 20, 1989; 320:1037-1043.)
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Publication:Medical Update
Date:Jun 1, 1989
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