DALLAS, Jan. 16 -- Potassium, either in the form of fruits and vegetables, or in supplements can lower high blood pressure, a risk factor for heart attack or stroke, Harvard researchers report in Hypertension: Journal of the American Heart Association.
Individuals should eat more fruits such as bananas, oranges and green leafy vegetables to help prevent high blood pressure, says Frank M. Sacks, M.D., professor of nutrition, Harvard School of Public Health. "If he or she already has high blood pressure, then they should eat a diet high in potassium or take supplements."
The study, which involved 300 women in the Nurses' Health Study, showed that potassium was far more important than magnesium or calcium in lowering blood pressure. In the past, it was hard to delineate which of these was more important or whether they worked together in lowering blood pressure.
The nurses, average age 39 years and weight 140 pounds, had an average blood pressure of 116/73 millimeters of mercury. They were divided into five groups with each receiving either potassium supplements, magnesium, calcium, a combination of the three, or a placebo. Blood pressures were taken over a 24-hour period.
Average changes in both systolic (when the heart contracts with each heartbeat) and diastolic (when the heart muscle is relaxed between beats) blood pressures were significant with potassium, but not with magnesium or calcium.
The daily 40 millimoles of potassium supplementation (about 1,600 milligrams) lowered systolic blood pressure by 2 mm of Hg and diastolic blood pressure by 1.7 mm of Hg. A glass of orange juice or a banana contains about 400 milligrams of potassium
While calcium and magnesium lowered blood pressure, the drop was not statistically significant. "Suprisingly, when we put the three together, the effect was no greater than potassium alone," he says. "In fact, it was a little lower."
The effect of potassium was small because the nurses' blood pressures were normal, Sacks says. "But previous studies have shown that potassium in people with high blood pressure has a greater effect of lowering blood pressure 4 to 5 mm Hg."
Co-authors are Walter C. Willett, M.D.; Angela Smith, B.A.; Lisa Brown, M.P.H.; and Bernard Rosner, Ph.D.; all with Harvard School of Public Health; &Co., Inc., and Thomas Moore, M.D., formerly of Harvard Medical School and now an employee of Merck and Co., Inc.
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