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 vitamin D intake. There was a decline in PTH in the vitamin D groups 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.
Trial registration: ClinicalTrials.gov NCT00762775.