Three doses of vitamin D on insulin resistance and osteocalcin measures in older women

Short‐term clinical studies suggest that vitamin D (VitD) supplementation influences osteocalcin (OC) levels during caloric restriction, and this is associated with lower insulin resistance (IR). In mice, the undercarboxylated form of OC (ucOC) acts as a circulating hormone to regulate insulin production and sensitivity. This one‐year long weight control study addresses whether vitamin D supplementation in healthy overweight/obese older women influences markers of insulin sensitivity and OC measures. Design Fifty‐eight obese/overweight women (age, 58 ± 6 years; body mass index, 30.1 ± 3.8 kg/m 2 , serum 25‐hydroxyvitamin D (25OHD), 27.1 ± 4.4 ng/ml, glucose, 86 ± 10.3 mg/dl, insulin, 7.2 ± 2.7 mIU/l) were randomly assigned to one of 3 doses of VitD (600 IU/d; 2000 IU/d; 4000 IU/d) with 1.2 Ca g/d. Serum was analyzed for 25OHD (total, free and bioavailable), OC, ucOC, glucose and insulin. An oral glucose tolerance test (OGTT; glucose area under the curve, AUC) was performed at 12 month. Homeostasis Model Assessment (HOMA) and quantitative insulin sensitivity check index (QUICKI) were calculated. Results At 1 year, serum 25OHD levels increased to 30.4 ± 5.2, 35.8 ± 4.5 and 41.5 ± 6.9 ng/ml, and differed between groups 600, 2000 and 4000 IU, respectively (p<0.05). Weight change was similar across groups (−3.0 ± 4.1%). There was an interaction between VitD group and time on glucose and QUICKI (p≤0.05). The decline in serum glucose and the increase in QUICKI was greater in the 2000 IU compared to the 600 IU group (p≤0.05) and did not differ significantly compared to the 4000 IU group. Insulin decreased to a similar extent between groups over time (p<0.05). There were no significant correlations between changes in total, free or bioavailable 25OHD and glycemic markers or OC measures. Conclusion Dietary vitamin D intake modestly affects glycemic markers in healthy overweight/obese older women. Support or Funding Information NIH‐AG12161, NJAES‐0153866