RBP4 and vitamin D deficiency: The aim of this study was to compare the production of selected adipokines, potentially involved in the pathogenesis of IBD – adiponectin, resistin, retinol binding protein 4 (RBP-4), adipocyte fatty acid-binding protein (A-FABP), and nesfatin-1 [15–21] in affected children and healthy controls according to the presence of vitamin D deficiency.