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

•We examined vitamin D3 supplementation (VitD) on glycemic indices and osteocalcin.•Women were assigned to weight loss or maintenance and 2500 or 400 IU/d VitD for 6 weeks.•The change in serum osteocalcin was explained by changes in 25OHD and insulin.•VitD and caloric restriction influences osteocalcin and favors insulin sensitivity.

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 R2 = 25.6%). Overall, vitamin D supplementation and CR influence serum osteocalcin levels and modestly favor improvements in insulin sensitivity.