• Elena Barengolts, Buvana Manickam, Yuval Eisenberg, Arfana Akbar, Subhash Kukreja, and Irina Ciubotaru.
• Endocr Pract. 2015 Jun 1; 21 (6): 604-12.

ObjectiveThis double-blind, randomized, controlled trial evaluated whether 12 months of high-dose vitamin D2 supplementation improved insulin sensitivity and secretion and glycemic status.MethodsAfrican-American males (AAM) with prediabetes (glycosylated hemoglobin [A1C] 5.7-6.4%), hypovitaminosis D (25-hydroxyvitamin D [25OHD] 5-29 ng/mL), and prevalent medical problems were supplemented with vitamin D3 (400 IU/day) and then randomized to weekly placebo or vitamin D2 (50,000 IU). The primary outcome was the change in oral glucose insulin sensitivity (OGIS, from an oral glucose tolerance test [OGTT]) after 12 months of treatment. Secondary outcomes included other glycemic indices, A1C, and incident diabetes.ResultsBaseline characteristics were similar in vitamin D-supplemented (n = 87) and placebo (n = 86) subjects completing the trial with average concentrations 14.4 ng/mL, 362 mL × min(-1) × m(-2), and 6.1% for 25OHD, OGIS and A1C, respectively. After 12 months, the vitamin D-supplemented group had a change in serum 25OHD +35 versus +6 ng/mL for placebo, P<.001; OGIS +7.8 versus -16.0 mL × min(-1) × m(-2) for placebo, P = .026; and A1C -0.01 versus +0.01% for placebo, P = .66. Ten percent of subjects in both groups progressed to diabetes. A posthoc analysis of participants with baseline impaired fasting glucose (IFG) showed that more subjects in the vitamin D subgroup (31.6%) than placebo (8.3%) returned to normal glucose tolerance, but the difference did not reach significance (P = .13).ConclusionThe trial does not provide evidence that 12 months of high-dose D2 repletion improves clinically relevant glycemic outcomes in subjects with prediabetes and hypovitaminosis D (NCT01375660).

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