Glucose regulation and association with Vitamin D and parathyroid hormone - differences across Middle Eastern and Caucasian ethnicities.

Background: Middle Eastern (ME) immigrants to Europe have a heavy burden of metabolic disorders including a higher prevalence of insulin resistance, T2D and obesity as compared to native-born Europeans. Vitamin D insufficiency and deficiency are prevalent conditions in people originating from the ME. Aims: To study the differences in the levels of 25(OH)D and parathyroid hormone (PTH) across ME and European ethnicity, and the effect of 25(OH)D and PTH on insulin action and secretion. Methods: Vitamin D and PTH levels were assessed in a population-based cohort of 918 participants (449 Swedes and 469 Iraqis) aged 30-75 years. The differences between the groups in the adjusted levels of Vitamin D and PTH were studied using multiple regression analysis. Differences in insulin action and secretion, in relation to risk markers including Vitamin D and PTH, were assessed using multiple regression analysis. Results: Vitamin D and PTH adjusted levels differed significantly between the groups; 92% of the Iraqi-born versus 45% of the Swedish-born individuals had Vitamin D levels below 50 nmol/L. The mean levels of PTH (SD) were higher in Iraqi-born compared to native Swedish-born (5.1 (2.3) vs. 3.8 (1.6) pmol/L, p = < 0.001). Insulin sensitivity was lower in Iraqi-born (79.16 vs. 98.97, β Conclusion: The ethnic differences in insulin action could be explained by differences in the levels of Vitamin D.