Material and Method: Forty-seven IFG and/or IGT subjects enrolled in the study. Subjects were randomized into three groups, control (n = 18), vitamin D2 (20,000 IU weekly, n = 19) or vitamin D3 (15,000 IU weekly, n = 10). Anthropometric variables were obtained at baseline and at 3-month. Oral glucose tolerance test was performed at baseline and at 3-month. Total serum 25(OH)D, 25(OH)D3, and 25(OH)D2 were measured by LC-MS/MS. Insulin resistance (HOMA-IR) and insulin secretion index (HOMA%B) were calculated by the homeostasis model assessment.

Results: The total 25(OH)D levels significantly increased from baseline in both the vitamin D2 and the vitamin D3 groups, while there was no change in the control group. D3 supplementation raised 25(OH)D3 significantly (+13.7±4.9 ng/mL, p<0.01) while D2 increased 25(OH)D2 levels (+25.9±4.2 ng/mL, p<0.001) but with a decrease in 25(OH)D3 (-13.1±3.1 ng/mL, p<0.001). Subjects were classified into two groups, i.e., control (n = 18) and D2 or D3 supplementations (n = 29). After three months, waist circumference (WC) significantly decreased in subjects of vitamin D supplementation group. Body weight (BW, p = 0.05), systolic blood pressure (SBP, p = 0.05), body mass index (BMI, p = 0.06), and HOMA-IR (p = 0.09) also tended to decrease. Subjects with an increase of total 25(OH)D levels ≥10 ng/mL (23 of 29 subjects) had significant decrease in HOMA-IR and increase in disposition index. Using robust regression analysis, we found the use of D3 was associated with a larger decrease in WC (coefficient = -3.5, p<0.001) independent of the change in total 25(OH)D and baseline BMI. No difference between D2 and D3 was observed for other metabolic measures.

Conclusion: Weekly supplementations of vitamin D2 (20,000 IU) or vitamin D3 (15,000 IU) improve metabolic phenotypes in subjects with prediabetes. D3 supplement may decrease waist circumference more than D2 supplement.

Keywords: Vitamin D, Vitamin D2, Vitamin D3, 25(OH)D, Prediabetes, Metabolic parameters