The Effect of Vitamin D Supplementation on the Glycemic Status and the Percentage of Body Fat Mass in Adults with Prediabetes: A Randomized Clinical Trial

Background Low serum levels of vitamin D are supposed to contribute to the incidence of diabetes; therefore, vitamin D supplementation may reduce the incidence of diabetes in individuals with prediabetes. Objectives The aim of this current study was to examine the effect of vitamin D supplementation on the glycemic status and percentage of body fat mass in adults with prediabetes. Methods In a 3-month randomized placebo-controlled supplementation trial, 120 eligible subjects were randomly assigned in a vitamin D or placebo group. They were stratified according to the percentage of body fat mass into four blocks to receive 1000 IU/daily vitamin D or an identical placebo tablet respectively, for 3 months. The study was conducted from January to March of 2016 in Urmia in the North West of Iran. Participants were adults aged 18 to 70 with prediabetes. The fasting blood sugar (FBS), glycated hemoglobin (HbA1c), homeostasis model assessment of insulin resistance (HOMA-IR), serum 25(OH)D levels, and percentage of body fat mass were assessed before and after the intervention. Results The comparison of changes from baseline between two groups showed a significant inverse association between the changes in serum 25(OH)D and changes in FBS (-4.64 ± 11.38 compared with -2.11 ± 9.15 for placebo; P = 0.03), HOMA-IR (-0.73 ± 4.2 compared with 0.44 ± 4.4 for placebo, P = 0.01) and serum insulin (-1.98 ± 15.25 compared with 2.47 ± 15.85 for placebo; P = 0.007) but not in the percentage of body fat mass (-0.28 ± 0.77 compared with -0.39 ± 2.82 for placebo; P = 0.39). Conclusions The study demonstrated that 1000 IU vitamin D supplementation for 3 months can decrease the insulin resistance in individuals with prediabetes; however, it has no significant effect on body fat mass percentage.