Effects of vitamin D(2) supplementation on insulin sensitivity and metabolic parameters in metabolic syndrome patients.

Background: Vitamin D deficiency has been linked to many of the characteristics of metabolic syndrome, but whether supplementation with vitamin D2 would improve insulin sensitivity or metabolic risk factors is not known.

Objective: To investigate effects of vitamin D2 supplementation on insulin sensitivity and metabolic parameters in metabolic syndrome patients.

Methods: An 8-week, prospective randomized, double-blind, double-dummy, parallel trial was conducted in patients with metabolic syndrome. Ninety patients were equally randomized to receive vitamin D2 40,000 IU per week, vitamin D2 20,000 IU per week, or placebo. Outcomes were assessed at baseline and at the end of the study.

Results: At week 8, serum 25(OH)D concentrations were increased significantly in both vitamin D2 groups (i.e., 20,000 IU and 40,000 IU) when compared with placebo group (11.72 ng/ml vs 2.80 ng/ml; p<0.001 and 15.74 ng/ml vs 2.80 ng/ml; p<0.001, respectively). Serum 25(OH)D concentrations in both vitamin D2 treatment groups were also significantly different (p=0.04). Insulin sensitivity assessed by homeostasis model assessment of insulin resistance (HOMA-IR) at week 8 in the three groups was not significantly different (p=0.36).

Conclusions: Vitamin D2 20,000 IU per week and 40,000 IU per week given for 8 weeks, were able to increase serum 25(OH)D concentrations significantly more than placebo group. However, HOMA-IR was not significantly different in the three groups. Our results do not support a positive effect of vitamin D2 on metabolic risk factors.