BIOCHEMICAL EFFECTS OF CALCIUM SUPPLEMENTATION IN POSTMENOPAUSAL WOMEN - INFLUENCE OF DIETARY CALCIUM INTAKE

We studied the biochemical effects of calcium supplementation during a 2-mo course in postmenopausal women ((x) over bar +/- SD: 64 +/- 5 y of age and 14.5 +/- 6.7 y since menopause). The effects on calcium hom eostasis and bone remodeling were assessed after 1 and 2 mo of daily a dministration of either calcium carbonate (1200 mg elemental Ca/d, n = 60) or a placebo (n = 56). The daily dietary calcium intake assessed before the beginning of calcium supplementation was 786 mg/d. We found a significant inverse relation between baseline intact parathyroid ho rmone (iPTH) and dietary calcium intake before supplementation (r = -0 .48, P = 0.0002). A significant increase in urinary excretion of pyrid inoline was observed when the dietary calcium intake was lower than th e median value. Calcium supplementation resulted in a significant incr ease in 24-h urinary calcium (39%, P < 0.02) and a significant reducti on of bone alkaline phosphatase at 2 mo and of all bone-resorption mar kers (hydroxyproline, pyridinoline, and deoxypyridinoline) at 1 and 2 mo without significant changes in 44-68 PTH fragments or iPTH concentr ations. When the dietary calcium intake was low (mean +/- SD: 576 +/- 142 mg/d), calcium supplementation was responsible for a greater incre ase in urinary calcium excretion and a greater decrease in markers of bone turnover. The greatest variations were observed for deoxypyridino line at 1 and 2 mo (-18.5%, P < 0.05) and for pyridinoline at 1 mo (-1 6.3%, P < 0.01). Two months of calcium supplementation in postmenopaus al women was efficient in reducing markers of bone turnover, with a gr eater effect in women with a low dietary calcium intake.