Alterations in calcium metabolism in young people at risk for primary hypertension: The Dutch hypertension and offspring study

Abstract

Several disturbances in calcium metabolism have been reported in primary hypertensive subjects. It is, however, not clear whether these alterations predate the development of hypertension or occur as a consequence of high blood pressure. We studied indexes of calcium metabolism in three groups of normotensive children with different familial predispositions for hypertension, based on parental blood pressure levels, with two, one, or no hypertensive parents. Plasma intact parathyroid hormone [1-84] was higher in the offspring of hypertensive parents compared with offspring of normotensive parents (difference, 0.58 pmol/L; standard error of the difference [SED], 0.24; p=0.02). Mean serum calcium levels were slightly reduced in the offspring of two hypertensive parents (-0.019 mmol/L, SED=0.013, p=0.17). Plasma magnesium and phosphate levels were lower in the offspring of hypertensive parents (-0.032 mmol/L [SED=0.016, p=0.05] and -0.045 mmol/L [SED=0.024, p=0.05], respectively). Mean 1,25-dihydroxyvitamin D3 levels were similar among the groups. No differences in dietary intake of calcium, phosphate, or fiber were found. Urinary calcium excretion per 24 hours and the ratio of 24-hour urinary calcium excretion to daily calcium intake were somewhat higher in the offspring of hypertensive parents. Renal fractional excretion of calcium was similar in the offspring of two hypertensive parents, and renal fractional excretion of phosphate was lower in the offspring of two hypertensive parents compared with offspring of two normotensive parents (-1.50%, SED=0.74, p=0.05). These findings indicate that changes in calcium metabolism may be implicated in the early pathogenesis of primary hypertension and suggest a reduced renal sensitivity to parathyroid hormone in those at risk for hypertension.