Objectives: Existing studies usually do not measure the free vitamin D in pediatric patients with inflammatory bowel disease (IBD) and not consider the effect of inflammation on vitamin D levels. The aim of our study was to evaluate the concentrations of vitamin D-binding protein (VDBP), total and free 25-hydroxyvitamin-D (25(OH)D), and to correlate these values with the disease activity markers.
Methods: Newly diagnosed children with IBD and a group of healthy controls (HCs) were enrolled. VDBP and total and free 25(OH)D levels were measured by enzyme-linked immunosorbent assay and compared using the Student t test. In each patient with IBD, the activity scores of disease and the main inflammation markers were correlated to total and free 25(OH)D levels. C-reactive protein was also measured in the control group, and it was related to VDBP by a linear regression test for all the groups.
Results: Fifty-one consecutive children were enrolled: IBD = 33, HC = 18. Levels of total 25(OH)D were higher in HC than in patients with IBD (P = 0.01). The free/total 25(OH)D ratio was, however, higher in patients with IBD compared to HC (P < 0.001). Finally, levels of VDBP were lower in patients with IBD than in HC (P = 0.001). A significant direct correlation was found between the free/total 25(OH)D ratio and the activity index of disease (r: 0.17; P = 0.01). Moreover, in patients with IBD and controls we found a significant indirect correlation between VDBP and C-reactive protein (r: 0.12; P = 0.01).
Conclusions: Inflammation inversely correlates to VDBP concentrations and patients with IBD, despite their deficiency in total 25(OH)D, have normal or even higher levels of free 25(OH)D.