Association Between Vitamin D and Inflammation and Diabetes Risk in Morbidly Obese Pre-Menopausal Women

Obesity is associated with low-grade inflammation, insulin resistance and low vitamin D status. Vitamin D has traditionally been known to involve in calcium homeostasis and prevent rickets; however, recently it has been recognized to inversely associate with many non-skeletal diseases and conditions including obesity and type 2 diabetes (T2DM). In vitro studies have demonstrated that vitamin D possesses anti-inflammatory properties. It remains unknown if the effect of vitamin D on insulin sensitivity is mediated by suppressing inflammation in human adipose tissues. The main objective of this study was to assess the association between vitamin D and insulin sensitivity and inflammation in morbidly obese pre-menopausal women. Obese women (n=76) were recruited from the University of Illinois at Chicago (UIC) Nutrition and Wellness Center and the UIC medical center bariatric surgery clinics. Insulin sensitivity/resistance was assessed by (1) Oral glucose insulin sensitivity (OGIS) index, derived from dynamic oral glucose tolerance test (OGTT), and (2) Homeostasis model of insulin resistance (HOMA-IR), calculated from fasting steady-state glucose and insulin. Also, to better understand the potential mechanism and the role circulating vitamin D (25OHD) plays in adipose tissue inflammation, we assessed messenger ribonucleic acid (mRNA) expression of vitamin D receptor (VDR) and various inflammatory genes in visceral (VAT) and subcutaneous adipose tissues (SAT) of obese women that underwent a restrictive bariatric procedure. We hypothesized that subjects with higher serum vitamin D levels would be less inflamed and more insulin sensitive and have increased expression of VDR and pro-inflammatory markers compared to those with lower serum vitamin D levels.