potassium, calcium and magnesium and blood pressure

Doug Skrecky (oberon@vcn.bc.ca)
Fri, 29 May 1998 05:25:51 -0700 (PDT)

Sacks FM. Willett WC. Smith A. Brown LE. Rosner B. Moore TJ.
Department of Nutrition, Harvard School of Public Health, Brigham and Women's
Hospital, Boston, Mass 02115, USA. fsacks:hsph.harvard.edu
Effect on blood pressure of potassium, calcium, and
magnesium in women with low habitual intake.
Hypertension. 31(1):131-8, 1998 Jan.
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.