Plasma 25-Hydroxyvitamin D Levels Are Favorably Associated With β-Cell Function

Objective: The association of hypovitaminosis D with type 2 diabetes is well recognized. Although hypovitaminosis D is associated with insulin resistance, there is much less information about its impact on beta-cell function in humans. Methods: We enrolled 150 healthy, glucose-tolerant subjects for the assessment of beta-cell function (acute insulin response) and insulin sensitivity index (ISI) using a hyperglycemic clamp. Adjusted beta-cell function (ABCF) was defined as the product of acute insulin response and ISI. The relations of plasma 25-hydroxyvitamin D [25(OH)D] level with insulin sensitivity and ABCF were examined. Results: Plasma 25(OH) D levels were positively associated with ABCF (P = 0.00004) and ISI (P < 0.00001). The associations remained significant after adjustment for age, sex, body mass index, physical activity, ethnicity, and season of study. Conclusions: Plasma 25(OH)D levels are positively association with both beta-cell function and insulin sensitivity. Our observations suggest the roles of vitamin D deficiency in the dual defect of type 2 diabetes.