Calcium attenuates cardiovascular reactivity to sodium and stress in blacks

The roles of dietary and behavioral factors in the etiology of hypertension are not well understood. Vulnerability to hypertension is thought to be affected by a complex interaction of nutritional, genetic, neurophysiological, and psychosocial influences. We studied cardiovascular reactivity to sodium and stress in a group of 29 normotensive young men who were vulnerable to hypertension by virtue of familial and/or racial factors. Subjects with positive and negative parental histories of hypertension were provided all meals for five days during which blood pressure was monitored before each meal. Two groups were given 300 mEq/day dietary sodium with either 1100 mg/day or 410 mg/day dietary calcium. A third group consumed a 10mEq sodium diet with low dietary calcium. On the fifth day of the diet all subjects were tested for cardiovascular reactivity using a modified Stroop test as a mentally challenging task. Adaptation of systolic blood pressure (SBP) from the first to the fifth breakfast was most pronounced in subjects consuming high calcium with high sodium. Perseveration of SBP reactivity to repeated mental challenge was found in subjects who consumed high sodium with low calcium and in subjects with positive parental histories of hypertension. The perseverative phenomenon was particularly well-defined in subjects who had the highest urinary excretion of calcium. Our findings suggest a prophylactic influence of dietary calcium and its retention on cardiovascular reactivity to sodium and stress. We also elucidate a theoretical proposition concerning the role of neurophysiological inhibitory capacity in the transition from normotension to the chronic dysregulatory state of essential hypertension.