Parathyroid Hormone Is Associated with Biomarkers of Insulin Resistance and Inflammation, Independent of Vitamin D Status, in Obese Adolescents

Background: 25-Hydroxyvitamin D [25(OH)D] and parathyroid hormone (PTH) have been shown to correlate with several markers of metabolic syndrome in adult populations. We evaluated the relationship between circulating intact parathyroid hormone (iPTH) and 25(OH)D and indices of metabolic syndrome in obese adolescents. Methods: Body mass index (BMI), body composition, 25(OH) D, iPTH, fasting lipids, glucose, high-sensitivity C-reactive protein (hsCRP), glycosylated hemoglobin (HbA1c), insulin, and the homeostatic model assessment for insulin resistance (HOMA-IR) were evaluated in 133 obese adolescents. Results: Vitamin D deficiency [25(OH) D < 50 nmol/L] was present in 45.1% of all patients, with higher prevalence in African-American (AA) and Hispanic (H) than Caucasian (C) subgroups (63.9% and 56.4% vs. 25.9%; P < 0.001). iPTH and 25(OH) D were inversely correlated (r=-0.75; P < 0.0001), with AA displaying a higher iPTH: 25(OH) D ratio than H and C subgroups (P < 0.05). Whereas fat mass (FM) was negatively correlated with 25(OH) D (r= -0.30; p < 0.001), it was positively correlated with iPTH levels (r = 0.38; P < 0.0001). Metabolic syndrome was identified in 57.9% of the cohort with higher iPTH, iPTH: 25(OH) D ratio, but lower 25(OH) D than participants without metabolic syndrome (P < 0.02). Whereas iPTH showed main effects for hsCRP (beta = 0.24, t = 2.61, P < 0.05) and triglycerides: high-density lipoprotein cholesterol (TG: HDL-C) (beta = 0.21, t = 2.13, p < 0.05), independent of serum 25(OH)D, it did not reveal a main effect for HOMA-IR. Conclusions: Metabolic syndrome is associated with a higher iPTH: 25(OH)D ratio than those without metabolic syndrome, implying greater risk of cardiovascular morbidities among AA subjects than other ethnic groups. Furthermore, the serum iPTH level is a predictor of chronic inflammation and dyslipidemia, independent of 25(OH)D.