Effect on blood pressure of potassium, calcium, and magnesium in women with low habitual intake.
Sacks FM, Willett WC, Smith A, Brown LE, Rosner B, Moore TJ
Hypertension 1998 Jan 31:1 131-8

Abstract
In populations, dietary intakes of potassium, calcium, and magnesium each have been inversely associated with blood pressure.
However, most clinical trials in normotensive populations have not found that dietary supplements of these minerals lowered blood
pressure. We tested the hypothesis that normotensive persons who have low habitual intake of these minerals would be particularly
responsive to supplementation. Three hundred normotensive women in the Nurses Health Study II (mean age, 39 years), whose
reported intakes of potassium, calcium, and magnesium were between the 10th and 15th percentiles, received for 16 weeks' duration
daily supplements of either potassium 40 mmol, calcium 30 mmol (1200 mg), magnesium 14 mmol (336 mg), all three minerals
together or placebos. At baseline, mean (+/-SD) 24-hour ambulatory blood pressures were 116+/-8 and 73+/-6 mm Hg systolic and
diastolic, respectively, and mean dietary intakes of potassium, calcium, and magnesium were 62+/-20 mmol/d, 638+/-265 mg/d, and
239+/-79 mg/d, respectively. The mean differences (with 95% confidence intervals) of the changes in systolic and diastolic blood
pressures between the treatment and placebo groups were significant for potassium, -2.0 (-3.7 to -0.3) and -1.7 (-3.0 to -0.4), but
not for calcium, -0.6 (-2.2 to 1.0) and -0.7 (-2.0 to 0.6), or for magnesium, -0.9 (-2.6 to 0.8) and -0.7 (-2.2 to 0.8). The
administration of calcium and magnesium with potassium did not enhance the effect of potassium alone, and the changes in blood
pressure were not significant -1.3 (-3.0 to 0.4) and -0.9 (-2.2 to 0.4). In conclusion, potassium, but not calcium or magnesium
supplements, has a modest blood pressure-lowering effect in normotensive persons with low dietary intake. This study strengthens
evidence for the importance of potassium for blood pressure regulation in the general population.