Vitamin D Not Linked to Insulin Sensitivity

Vitamin D concentrations have no independent association with insulin sensitivity or beta-cell function in black and white youth, according to a study.

Kumaravel Rajakumar, M.D., of the University of Pittsburgh School of Medicine, and associates analyzed plasma 25-hydroxyvitamin D (25[OH]D) concentrations and beta-cell function to determine their relationship with insulin sensitivity and disposition index (DI) in 183 healthy black and white youth aged 8 to 18 years.

The researchers found that, for whites, there were no differences in hemoglobin A1c, fasting glucose and insulin, insulin sensitivity, or DI across quartiles of plasma 25(OH)D. In the highest quartile of 25(OH)D there was significantly higher insulin sensitivity and DI for blacks, but this disappeared after adjusting for adiposity measures. When adjusting for adiposity, the difference in insulin sensitivity between nondeficient and deficient black youth also disappeared.

"In conclusion, our data show no independent relationship between plasma 25(OH)D and in vivo insulin sensitivity and beta-cell function relative to insulin sensitivity in otherwise healthy black and white youth," the authors write. "It remains to be determined whether similar or different relationships will be found in youth with dysglycemia and whether vitamin D optimization in vitamin D-deficient youth will enhance insulin sensitivity and beta-cell function."