Dietary cation intake and blood pressure in black girls and white girls.

The authors examined the relative importance of dietary sodium, potassium, calcium, and magnesium intakes as correlates of blood pressure in a cross-sectional analysis of 987 black and 1,043 white 9- and 10-year-old girls from Richmond, California, Cincinnati, Ohio, and Washington, DC, who were enrolled in the National Heart, Lung, and Blood Institute Growth and Health Study between January 1987 and May 1988. Dietary intake was measured using a 3-day food record. Dietary cation intake was not associated with blood pressure in black girls. An inverse association between magnesium intake and diastolic (fifth Korotkoff phase) blood pressure was found in white girls (p < 0.01). After controlling for factors often associated with blood pressure, such as pulse rate, body mass index, and household income, the authors found that dietary magnesium intake (range, 53-511 mg/day) continued to be associated with diastolic (fifth Korotkoff phase) blood pressure in white girls, such that each 100-mg/day increase in intake was associated with a 3.22-mmHg decrease in diastolic pressure (95% confidence interval -5.70 to -0.75). However, after adjustment for dietary fiber intake, the authors were no longer able to discern an association between dietary magnesium intake and blood pressure. They conclude that the body mass index and pulse rate are the strongest correlates of blood pressure in 9- and 10-year-old black girls and white girls and that studies examining the relation between dietary magnesium and blood pressure should control for the effects of dietary fiber intake.