Vitamin D insufficiency and insulin resistance in obese adolescents

• Published in: Therapeutic Advances in Endocrinology and Metabolism Vol. 5; no. 6; pp. 166 - 189
• Main Authors: Peterson, Catherine A., Tosh, Aneesh K., Belenchia, Anthony M.
• Format: Book Review Journal Article
• Language: English
• Published: London, England SAGE Publications 01.12.2014; SAGE Publishing
• Subjects: Reviews; insulin sensitivity; adolescent obesity; vitamin D insufficiency; hypovitaminosis D; glucose tolerance; diabetes; insulin resistance; vitamin D deficiency
• ISSN: 2042-0188; 2042-0196
• DOI: 10.1177/2042018814547205

Obese adolescents represent a particularly vulnerable group for vitamin D deficiency which appears to have negative consequences on insulin resistance and glucose homeostasis. Poor vitamin D status is also associated with future risk of type 2 diabetes and metabolic syndrome in the obese. The biological mechanisms by which vitamin D influences glycemic control in obesity are not well understood, but are thought to involve enhancement of peripheral/hepatic uptake of glucose, attenuation of inflammation and/or regulation of insulin synthesis/secretion by pancreatic β cells. Related to the latter, recent data suggest that the active form of vitamin, 1,25-dihydroxyvitamin D, does not impact insulin release in healthy pancreatic islets; instead they require an environmental stressor such as inflammation or vitamin D deficiency to see an effect. To date, a number of observational studies exploring the relationship between the vitamin D status of obese adolescents and markers of glucose homeostasis have been published. Most, although not all, show significant associations between circulating 25-hydroxyvitamn D concentrations and insulin sensitivity/resistance indices. In interpreting the collective findings of these reports, significant considerations surface including the effects of pubertal status, vitamin D status, influence of parathyroid hormone status and the presence of nonalcoholic fatty liver disease. The few published clinical trials using vitamin D supplementation to improve insulin resistance and impaired glucose tolerance in obese adolescents have yielded beneficial effects. However, there is a need for more randomized controlled trials. Future investigations should involve larger sample sizes of obese adolescents with documented vitamin D deficiency, and careful selection of the dose, dosing regimen and achievement of target 25-hydroxyvitamn D serum concentrations. These trials should also include clamp-derived measures of in vivo sensitivity and β-cell function to more fully characterize the effects of vitamin D replenishment on insulin resistance.