Discrepant influence of vitamin D status on parathyroid hormone and bone mass after two years of calcium supplementation.
OBJECTIVE
To investigate the influence of vitamin D status on parathyroid hormone and bone mass after a 2-year supplementation of calcium alone.


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.


METHODS
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 (4.4 +/- 1.7 vs 4.7 +/- 1.9 pmol/l, P < 0.01), improved lumbar BMD (1.031 +/- 0.12 vs 1.004 +/- 0.12 g/cm(2), P < 0.001) and total hip BMD (0.890 +/- 0.10 vs 0.883 +/- 0.10 g/cm(2), P < 0.001) without change in femoral neck BMD. In the placebo group, PTH level significantly increased (4.8 +/- 1.6 vs 4.5 +/- 1.5 pmol/l, P < 0.001), lumbar BMD slightly increased (1.027 +/- 0.14 vs 1.018 +/- 0.14 g/cm(2), P < 0.001), total hip and femoral neck BMD decreased (0.876 +/- 0.11 vs 0.887 +/- 0.11 g/cm(2), P < 0.001 and 0.783 +/- 0.10 vs 0.798 +/- 0.10 g/cm(2), P < 0.001, 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 (-5.6 +/- 26.7%vs 1.3 +/- 27.2%, P < 0.05). 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 (-0.6 +/- 3.2%vs 0.5 +/- 2.9%, P < 0.05).


CONCLUSIONS
Calcium supplementation appears to affect femoral bone mass less in Thai postmenopausal women with adequate vitamin D status, despite higher suppression of PTH.
Chailurkit
La-or
LO
Department of Medicine, Faculty of Medicine, Ramathibodi Hospital, Bangkok 10400, Thailand. ralcl@mahidol.ac.th
Saetung
Sunee
S
Thakkinstian
Ammarin
A
Ongphiphadhanakul
Boonsong
B
Rajatanavin
Rajata
R
D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D015519:Bone Density / Q000187:drug effects*; D002118:Calcium / Q000494:pharmacology / Q000627:therapeutic use*; D019587:Dietary Supplements; D004311:Double-Blind Method; D005260:Female; D006304:Health Status; D006801:Humans; D008875:Middle Aged; D015663:Osteoporosis, Postmenopausal / Q000097:blood / Q000517:prevention & control; D010281:Parathyroid Hormone / Q000097:blood*; D010919:Placebos; D013997:Time Factors; D014807:Vitamin D / Q000097:blood*
D010281:Parathyroid Hormone; D010919:Placebos; D014807:Vitamin D; D002118:Calcium