Response of several markers of bone collagen degradation to calcium supplementation in postmenopausal women with low calcium intake

Abstract

We investigated the response of bone-specific resorption markers in fasting urine samples from postmenopausal women with low daily dietary calcium (Ca) intake (<800 mg/day) who received either Ca supplementation (1200 mg/day, n = 18) or placebo (n = 14) for 2 months. We measured urinary hydroxyproline, total pyridinoline, and deoxypyridinoline by HPLC, and free deoxypyridinoline (i-F-Dpd) and N- and C-telopeptide fragments of type I collagen (NTX and CTX) by immunoassays. Before supplementation, the urine concentrations of bone resorption markers in the 32 subjects were not statistically different from those measured in 21 subjects with daily dietary Ca intake >800 mg/day. In contrast to the placebo group, Ca supplementation decreased all collagen-related degradation markers except i-F-Dpd as early as the first month. The magnitude of response after 2 months of Ca supplementation, expressed as mean percentage of decrease from baseline values or as individual Z scores, was greatest for the telopeptide assays. Furthermore, the percentage of change assessed at 2 months was greater than the within-person biological variability (CV) assessed in the placebo-treated women for NTX and CTX, whereas for the other markers the percentage of change was very close of the within-person CVs. We conclude that cross-linked telopeptide fragments of type I collagen most sensitively reflect the change in bone resorption after Ca supplementation.