Does vitamin D3 supplementation improve glucose homeostasis in overweight or obese women? A double-blind, randomized, placebo-controlled clinical trial.

AIMS: Vitamin D deficiency is considered as a risk factor in cardiometabolic disorders, including cardiovascular diseases, hypertension and Type 2 diabetes mellitus. We have investigated the effect of vitamin D3 supplementation on glucose homeostasis in healthy overweight and obese women.

METHODS: In a double-blind randomized placebo-controlled clinical trial, 77 healthy overweight or obese women (mean age 38 ± 8 years; BMI 29.9 ± 4.2 kg/m(2)) were randomly assigned to the vitamin D3 group (25 μg/day as cholecalciferol tablets) or the placebo group. Selected anthropometric indices, glucose, insulin, HbA(1c) and homeostasis model assessment of insulin resistance at baseline and after 12 weeks were measured. Dietary intakes using 24-h food recall and food frequency questionnaires were assessed. Physical activity was assessed by the International Physical Activity Questionnaire. Adjusted mean differences were calculated using analysis of covariance. Correlation coefficients were calculated by Pearson's analysis.

RESULTS: Mean fasting blood glucose concentrations declined in the vitamin D3 and placebo groups (-0.28 ± 0.4 vs. -0.65 ± 0.4 mmol/l, P < 0.001) and the mean percentage of HbA(1c) was decreased (-13 ± 18 vs. -19 ± 17 mmol/l, P = 0.06) in both groups, respectively. Mean 25-hydroxyvitamin D concentrations increased in the vitamin D3 and placebo groups (38.2 ± 32 vs. 4.6 ± 14 nmol/l, P < 0.001), respectively. There was a significant correlation between HbA(1c) and 25-hydroxyvitamin D concentrations (r = -0.271; P = 0.018).

CONCLUSIONS: The results indicate that the vitamin D3 supplement of 25 μg/day had no beneficial effect on glycaemic indices in healthy overweight or obese women.