OBJECTIVEThere has been conflicting evidence regarding the potential role of vitamin D in glucose homeostasis. This study was designed to investigate the effect of highdose vitamin D3 treatment on b-cell function, insulin sensitivity, and glucose tolerance in subjects with prediabetes or diet-treated type 2 diabetes.
RESEARCH DESIGN AND METHODSSubjects (n = 44) were randomized to 30,000 IU vitamin D3 once weekly or placebo for 8 weeks. Hyperglycemic clamp assessed first-phase (0-12 min) and secondphase (12-120 min) insulin response, insulin sensitivity, and disposition index (DI). An oral glucose tolerance test assessed glucose tolerance and glycosylated hemoglobin assessed glycemic control.
CONCLUSIONSThis study gives no support for any substantial effect of high-dose vitamin D treatment for 8 weeks in prediabetes or diet-treated type 2 diabetes on b-cell function, insulin sensitivity, or glycemic control.Evidence suggesting that vitamin D has an important role in glucose homeostasis has accumulated during the last three decades. A meta-analysis concluded that observational studies have demonstrated a relatively consistent association between low vitamin D serum levels and prevalence of type 2 diabetes or metabolic syndrome (1). Moreover, cohort studies have shown an inverse association between baseline