Discrepant influence of vitamin D status on parathyroid hormone and bone mass after two years of calcium supplementation

P>Objective To investigate the influence of vitamin D status on parathyroid hormone and bone mass after a 2-year supplementation of calcium alone. Patients and Methods Randomized, double-blind, placebo-controlled clinical trial, in healthy postmenopausal women without osteoporosis: three hundred and thirty-six subjects aged 60-97 years were studied and randomized to receive elemental calcium 500 mg/day (n = 175) or placebo (n = 161) for 2 years. Measurements Changes in parathyroid hormone (PTH) and bone mineral density (BMD) from baseline and vitamin D status. Values are presented as means +/- SD. Results After 2 years, subjects with calcium supplementation had significant decrease in plasma PTH level (4 center dot 4 +/- 1 center dot 7 vs 4 center dot 7 +/- 1 center dot 9 pmol/l, P < 0 center dot 01), improved lumbar BMD (1 center dot 031 +/- 0 center dot 12 vs 1 center dot 004 +/- 0 center dot 12 g/cm2, P < 0 center dot 001) and total hip BMD (0 center dot 890 +/- 0 center dot 10 vs 0 center dot 883 +/- 0 center dot 10 g/cm2, P < 0 center dot 001) without change in femoral neck BMD. In the placebo group, PTH level significantly increased (4 center dot 8 +/- 1 center dot 6 vs 4 center dot 5 +/- 1 center dot 5 pmol/l, P < 0 center dot 001), lumbar BMD slightly increased (1 center dot 027 +/- 0 center dot 14 vs 1 center dot 018 +/- 0 center dot 14 g/cm2, P < 0 center dot 001), total hip and femoral neck BMD decreased (0 center dot 876 +/- 0 center dot 11 vs 0 center dot 887 +/- 0 center dot 11 g/cm2, P < 0 center dot 001 and 0 center dot 783 +/- 0 center dot 10 vs 0 center dot 798 +/- 0 center dot 10 g/cm2, P < 0 center dot 001, respectively). When subjects were classified according to baseline 25-hydroxyvitamin D [25(OH)D] levels into those with 25(OH)D in the lower tertile (lowVitD) and those in the middle and upper tertiles combined (normVitD). The degree of PTH suppression after calcium supplementation was significantly higher in the normVitD compared to the lowVitD groups (-5 center dot 6 +/- 26 center dot 7%vs 1 center dot 3 +/- 27 center dot 2%, P < 0 center dot 05). No effect of vitamin D status on the change in lumbar BMD after calcium supplementation was demonstrated. Despite the higher suppression of PTH, there was a slight decrease in femoral neck BMD after calcium supplementation in the normVitD group while femoral neck BMD was more or less maintained in the lowVitD group (-0 center dot 6 +/- 3 center dot 2%vs 0 center dot 5 +/- 2 center dot 9%, P < 0 center dot 05). Conclusion Calcium supplementation appears to affect femoral bone mass less in Thai postmenopausal women with adequate vitamin D status, despite higher suppression of PTH.