Vitamin D, parathyroid hormone levels and insulin sensitivity among obese young adult Saudis

Objectives: To determine alterations of vitamin D and parathyroid hormone levels and their relationship to insulin resistance among a sample of healthy young adult obese Saudis and to identify factors that might predict these alterations. Methods: Age and gender matched obese young (aged 18-25 years) adult Saudis (N=76) with body mass index of >= 30 and their lean controls (N=84) were recruited after fulfilling exclusion and inclusion criteria from attendees of health facility at King Faisal University, Saudi Arabia. Selected participants were invited to a personal interview to gather information regarding socio-demographics. Fasting blood samples were assessed for the following essays: serum calcium, 25 OH vitamin D, inorganic phosphorus, intact parathyroid hormone (iPTH), serum insulin, fasting glucose, renal and liver function tests. Results: Vitamin D levels were significantly higher in lean controls, and showed significant decline in relation to obesity classes, hypovitaminosis D was found in 30% (38.2% obese vs. 22.7% in lean) and deficiency in 17.5% of subjects; (19% vs. obese 15.8%). iPTH was significantly higher in obese subjects. Secondary hyperparathyroidism was found in 48.1% (60.5% obese vs. 36.9% controls). Regression analysis showed that body mass index, serum calcium and creatinine levels were the main predictors for vitamin D level. Vitamin D is positively associated with fasting blood sugar (r=-.133, P=0.09) and beta cell function index (r=.192, P=0.08), negatively associated with HOMA-IR (r=-.122, P=.34) but without statistical significance after controlling of possible confounders. Conclusion: Vitamin D level among young adult Saudi obese is negatively associated by body mass index and classes of obesity. Negative associations between vitamin D, iPTH levels and HOMA-IR exist but without statistical significance.