Three doses of vitamin D, bone mineral density, and geometry in older women during modest weight control in a 1-year randomized controlled trial.

The effects of higher than recommended vitamin D doses on bone mineral density (BMD) and quality are not known. In this study, higher intakes, in postmenopausal women undergoing weight control over 1 year, had no effect on areal or volumetric BMD but prevented the deterioration in cortical bone geometry. INTRODUCTION: Studies examining how bone responds to a standard dose of vitamin D supplementation have been inconsistent. In addition, the effects of higher doses on BMD and quality are not known. Postmenopausal women undergoing weight control to improve health outcomes are particularly at risk for bone loss and might benefit from supplemental vitamin D intake above the recommended allowance. METHODS: This 1-year-long, randomized, double-blind controlled study addresses whether vitamin D supplementation, in healthy overweight/obese older women, affects BMD and bone structural parameters. In addition, bone turnover and serum total, free, and bioavailable 25-hydroxyvitamin D (25OHD) responses to one of three daily levels of vitamin D3 (600, 2000, 4000 IU) with 1.2 Ca g/day during weight control were examined. RESULTS: Fifty-eight women (age, 58 ± 6 years; body mass index, 30.2 ± 3.8 kg/m2, serum 25OHD, 27.3 ± 4.4 ng/mL) were randomized to treatment. After 1 year, serum 25OHD concentrations increased to 26.5 ± 4.4, 35.9 ± 4.5, and 41.5 ± 6.9 ng/mL, in groups 600, 2000, and 4000 IU, respectively, and differed between groups (p < 0.01). Weight change was similar between groups (-3.0 ± 4.1 %). Cortical (Ct) thickness of the tibia changed by -1.5 ± 5.1 %, +0.6 ± 3.2 %, and +2.0 ± 4.5 % in groups 600, 2000, and 4000 IU, respectively, and each group was significantly different from each other (p < 0.05). CONCLUSION: The decline in Ct thickness was prevented with higher vitamin D3 supplementation, but there were no other significant changes due to treatment over 1 year. Whether these findings translate to changes in biomechanical properties leading to reduced fracture risk should be addressed in future studies.

Vitamin D supplementation during short-term caloric restriction in healthy overweight/obese older women: Effect on glycemic indices and serum osteocalcin levels.

The effect of vitamin D supplementation and caloric restriction (CR) on glycemic indices and osteocalcin (OC) is not clear. In this randomized controlled double blind trial, we examined whether vitamin D3 supplementation at 2500 IU/d (D) or placebo has differential effects on markers of insulin sensitivity and bone turnover in overweight/obese postmenopausal women during 6 weeks of caloric restriction (weight loss; WL, n = 39) compared to weight maintenance (WM, n = 37). Seventy-six women (57 ± 6 years) completed this study and the WL groups lost 4 ± 1% of body weight. Baseline serum 25-hydroxyvitamin D (25OHD) was 24.8 ± 5.6 ng/mL at baseline; the rise was greatest in WL-D group (p < 0.05). There was an interaction between vitamin D intake and weight on serum OC, insulin, glucose and markers of insulin sensitivity (p < 0.05). The change in OC was explained by changes in serum 25OHD and insulin (model R(2) = 25.6%). Overall, vitamin D supplementation and CR influence serum osteocalcin levels and modestly favor improvements in insulin sensitivity.