EFFECTS OF VITAMIN-D ON INSULIN AND GLUCAGON-SECRETION IN NON-INSULIN-DEPENDENT DIABETES-MELLITUS

Vitamin D has been shown to increase insulin release from pancreatic i slet cells in vitro, and to improve insulin secretion in vitamin D-def icient animals. Few attempts have been made to evaluate this issue dir ectly in humans. We studied 35 otherwise healthy diabetic subjects in the early spring at the seasonal nadir of 25-hydroxyvitamin D [25(OH)D ] concentrations (mean 35 +/- 7 nmol/L). Easting glucose, insulin, C-p eptide, and glucagon concentrations, and their responses to Sustacal s timulation were not related to indexes of mineral metabolism. In 20 su bjects, a double-blinded, placebo-controlled, crossover trial of 1,25- dihydroxyvitamin D [1,25(OH)(2)D] treatment (1 mu g/d for 4 d) had no effect on fasting or stimulated glucose, insulin, C-peptide, or glucag on concentrations. However, insulin and C-peptide responses to Sustaca l after 1,25(OH)(2)D treatment were related to duration of diabetes (r (2) = 0.28, P = 0.052 and r(2) = 0.25, P = 0.002, respectively) in tha t short duration correlated with improvement after 1,25(OH)(2)D treatm ent. Hence, vitamin D nutrition, or 1,25(OH)(2)D therapy, had no major effect on glucose homeostasis in non-insulin-dependent diabetes melli tus.