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(Hypertension. 1997;29:531.)
© 1997 American Heart Association, Inc.

State-of-the-Art-Lecture

Oral Calcium Supplementation Reduces Intraplatelet Free Calcium Concentration and Insulin Resistance in Essential Hypertensive Patients

Miquel Sánchez; Alejandro de la Sierra; Antonio Coca; Esteban Poch; Vicent Giner; Alvaro Urbano-Márquez

From the Hypertension Unit, Departments of Internal Medicine and Nephrology (E.P.), Hospital Clínic, University of Barcelona, Spain.

Correspondence to Alejandro de la Sierra, MD, Hypertension Unit, Department of Internal Medicine, Hospital Clínic, Villarroel 170, 08036-Barcelona, Spain. E-mail iserte{at}medicina.ub.es

We evaluated the effect of oral calcium supplementation on blood pressure, calcium metabolism, and insulin resistance in essential hypertension. After receiving a standard diet with 500 mg of calcium per day during a 4-week period, 20 nondiabetic, essential hypertensive patients were randomized in a double-blind fashion to receive oral calcium supplementation (1500 mg of calcium per day) or placebo for 8 weeks. At the end of the 4-week period of low-calcium diet and after the 8-week period of intervention, we measured blood pressure (by both office and 24-hour ambulatory blood pressure monitoring), calcium-regulating hormones [urinary hydroxyproline and serum osteocalcin, parathormone, and 1,25(OH)₂-vitamin D₃], intra-platelet free calcium concentration, fasting plasma glucose and insulin levels, and the insulin-sensitivity index (euglycemic-hyperinsulinemic clamp). Compared with patients maintained 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 µg/L; P=.0015), parathormone (from 4.20±0.38 to 3.30±0.36 pmol/L; P=.0003), and 1,25(OH)₂-vitamin D₃ (from 98.0±11.0 to 61.6±5.7 pmol/L; P=.0062). Likewise, we found a significant reduction in intraplatelet free calcium concentration (from 35.9±1.2 to 26.5±0.8 nmol/L; P=.0005) and fasting 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·^-1; P=.0007). None of these parameters were significantly modified in patients maintained at low calcium intake. Office and 24-hour mean values of systolic and diastolic blood pressure did not change after 8 weeks of oral calcium supplementation or placebo.

Key Words: calcium, dietary • calcium supplements • intracellular free calcium • insulin resistance • hypertension

Abbreviations: ABPM = ambulatory blood pressure monitoring • BP = blood pressure • DBP = diastolic blood pressure • Fura 2-AM = Fura 2-acetoxymethylester • HBS = HEPES-buffered saline • PRP = platelet-rich plasma • SBP = systolic blood pressure

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