Calcium and vitamin D supplementation in postmenopausal women

Context: Bone health is influenced by the intake of both calcium and vitamin D. Objective: Our objective was to evaluate the influence of calcium and vitamin D supplementation on PTH and bone turnover. Setting, Patients, and Design: At an ambulatory research center, 159 postmenopausal healthy white women participated in this double-blind, placebo-controlled parallel, longitudinal factorial study that was 6 months in duration. Interventions: Subjects were randomly allocated to 4 groups: 1) double placebo, 2) calcium (1200 mg daily) plus placebo, 3) vitamin D₃ (100 μg) plus placebo, and 4) vitamin D₃ and calcium. Serum and urine were collected fasting and 2 hours after a calcium load at baseline and at 3 and 6 months. Main Outcome Measures: Serum PTH, cross-linked C-telopeptide (CTX), and procollagen type I N-terminal propeptide (P1NP) were measured. Results: Before study medication, a calcium load resulted in a decline in PTH and CTX and an increase in urinary calcium excretion. Serum CTX and P1NP declined over time with calcium supplementation but did not change with increased vitaminDintake. There was a decline in PTH in the vitaminDgroups in the fasting state compared with placebo. Suppression of PTH was greater after a calcium load in the vitamin D groups. A calcium load decreased PTH and CTX and raised urinary calcium. Conclusions: Fasting PTH declines with vitamin D supplementation. PTH declines after calcium intake. Supplementation of the diet with 1200 mg calcium/d reduces bone turnover markers, whereas supplementation with up to100 μg vitamin D₃/d does not.