ORAL CALCIUM SUPPLEMENTATION REDUCES INTRAPLATELET FREE CALCIUM-CONCENTRATION AND INSULIN-RESISTANCE IN ESSENTIAL HYPERTENSIVE PATIENTS

We evaluated the effect of oral calcium supplementation on blood press ure, calcium metabolism, and insulin resistance in essential hypertens ion. After receiving a standard diet with 500 mg of calcium per day du ring a 4-week period, 20 nondiabetic, essential hypertensive patients were randomized in a double-blind fashion to receive oral calcium supp lementation (1500 mg of calcium per day) or placebo for 8 weeks. At th e end of the 4-week period of low-calcium diet and after the 8-week pe riod of intervention, we measured blood pressure (by both office and 2 4-hour ambulatory blood pressure monitoring), calcium-regulating hormo nes [urinary hydroxyproline and serum osteocalcin, parathormone, and 1 ,25(OH)(2)-vitamin D-3], intraplatelet free calcium concentration, fas ting plasma glucose and insulin levels, and the insulin-sensitivity in dex (euglycemic-hyperinsulinemic clamp). Compared with patients mainta ined at low calcium intake, essential hypertensive patients under oral calcium supplementation significantly reduced serum osteocalcin (from 22.2 +/- 1.9 to 17.9 +/- 2.0 mu g/L; P = .0015), parathormone (from 4 .20 +/- 0.38 to 3.30 +/- 0.36 pmol/L, P = .0003), and 1,25(OH)(2)-vita min D-3 (from 98.0 +/- 11.0 to 61.6 +/- 5.7 pmol/L; P = .0062). Likewi se, we found a significant reduction in intraplatelet free calcium con centration (from 35.9 +/- 1.2 to 26.5 +/- 0.8 nmol/L; P = .0005) and f asting plasma insulin levels (from 71.8 +/- 5.9 to 64.6 +/- 6.2 pmol/L ; P = .05) and a significant increase in the insulin-sensitivity index (from 2.89 +/- 0.77 to 4.00 +/- 0.95 mg . kg(-1). min(-1); P = .0007) . None of these parameters were significantly modified in patients mai ntained at low calcium intake. Office and 24-hour mean values of systo lic and diastolic blood pressure did not change after 8 weeks of oral calcium supplementation or placebo.