Effect of isolated vitamin D supplementation on bone turnover markers in younger postmenopausal women: a randomized, double-blind, placebo-controlled trial.

Abstract

The purpose of this study is to evaluate the effect of VD supplementation alone on bone turnover markers in younger postmenopausal women. In this double-blind, placebo-controlled trial, 160 women were randomized into the VD group (supplementation with 1000IU of vitamin D3/day, orally; n = 80) or placebo group (n = 80). Women aged 50-65years with amenorrhea ≥ 12months and normal bone mineral density were included. The intervention lasted 9months, and the participants were assessed at the beginning and end of treatment. Serum levels of total calcium, parathormone (PTH), alkaline phosphatase (AP), and 24-h urine calcium were determined. Serum C-terminal telopeptide of type I collagen (s-CTX) and procollagen type 1 N-terminal propeptide (P1NP) were measured by immunoassay as markers of bone resorption and formation, respectively. Plasma 25-hydroxyvitamin-D [25(OH)D] concentrations were measured by HPLC. Intention-to-treat analysis was performed using ANOVA, Student's t test, Tukey's test, and gamma distribution. Over the period of 9months, 25(OH)D concentrations increased from 15.0 ± 7.5 to 27.5 ± 10.4ng/mL (+ 45.4%) in the VD group and decreased from 16.9 ± 6.7 to 13.8 ± 6.0ng/mL (- 18.5%) in the placebo group (p< 0.001). There was a decrease (- 21.3%) of PTH levels in the VD group with a significant difference between groups at the end of the study (p< 0.001). No significant differences were observed in the other laboratory parameters (total calcium, AP, and calciuria) in either group (p> 0.05). A comparison of bone turnover markers showed a significant reduction in of s-CTX (- 24.2%, p< .0001) and P1NP (- 13.4%, p= 0.003) levels in the VD group. No significant variations in bone turnover markers were observed in the placebo group (s-CTX, - 6.9%, p= 0.092 and P1NP, - 0.6%, p= 0.918). In younger postmenopausal women with VD deficiency, isolated supplementation with 1000IU of vitamin D3 for 9months is associated with a reduction in bone turnover markers. However, any between-group differences was not observed in bone turnover markers.