The Relative Influence of Calcium Intake and Vitamin D Status on Serum Parathyroid Hormone and Bone Turnover Biomarkers in a Double-Blind, Placebo-Controlled Parallel Group, Longitudinal Factorial Design

Background: Adequate calcium and vitamin D are needed to maintain calcium balance. Objective: Our objective was to examine the influence of calcium intake and vitamin D exposure separately and their interaction on biomarkers of calcium sufficiency. Design: Healthy men and women, age 20-80 yr, were randomly allocated to four groups: 1) double placebo, 2) calcium (1200 mg daily) plus placebo, 3) vitamin D-3 (100 mu g) plus placebo, and 4) vitamin D-3 and calcium. Fasting serum and urine as well as serum and urine 2 h after a calcium load (600 mg of calcium carbonate) were obtained at baseline and 3 months. Results: Ninety-nine participants were randomized; 78 completed the study. Baseline demographics, protein intake and laboratory studies did not differ among the four groups. Study medication compliance was 90%. Fasting bone turnover markers declined after 3 months only in the two groups given calcium supplements and increased in the vitamin D-3 plus placebo calcium group. The calcium load resulted in a decrease in PTH and in bone turnover markers that did not differ among groups. Urinary calcium excretion increased in the combined group. Mean serum 25-hydroxyvitamin D increased from a baseline of 67 (18 SD) nmol/liter to 111 (30 SD) nmol/liter after vitamin D supplementation. Conclusion: Increased habitual calcium intake lowered markers of bone turnover. Acute ingestion of a calcium load lowered PTH and bone turnover markers. Additional intake of 100 mu g/d vitamin D-3 did not lower PTH or markers of bone turnover. (J Clin Endocrinol Metab 95: 3216-3224, 2010)