Background: Vitamin D is an important regulator factor of the immune system and induces the development of self-tolerance. An association between vitamin D deficiency and inflammatory bowel diseases (IBD) has been described. Studies examining vitamin D levels in IBD usually do not consider the effect of inflammation on vitamin D and do not calculate the unbound, free vitamin D, which is the active form. The aim of our study was to investigate the levels of total 25-hydroxyvitamin-D (T-25OH-D) and free 25-hydroxyvitamin-D (F-25OH-D) in a cohort of IBD pediatric patients and to correlate these values with the disease activity and the markers of inflammation.
Methods: Between January 2015 and May 2016 we enrolled all consecutive children with a new diagnosis of IBD (group A), a group of IBD patients at follow-up in clinical remission (group B) and a group of age- and sex- matched healthy controls (group C). In each subject T-25OH-D and F-25OH-D levels were measured with an enzyme-linked immunosorbent assay (ELISA). Comparison between groups were made using non-parametric Mann-Whitney test. The disease activity was measured with Pediatric Crohn Disease Activity Index and Pediatric Ulcerative Colitis Activity Index for CD and UC, respectively. Moreover, as markers of inflammation, C reactive protein and and fecal calprotectin were measured and they were correlated to T-25OH-D and F-25OH-D levels by a linear regression test.
Results: Sixthy-four consecutive children were enrolled (group=n): group A=37, group B=27 and group C=18. Levels of T-25OH-D were higher in group A than in group B (19.9±1.7 ng/ml vs 14.2±1.3ng/ml; p=0.01) but were lower in both groups A and B when compared to group C (19.9±1.7 ng/ml vs 28.2±2.8 ng/ml; p=0.008 and 14.2±1.3ng/ml vs 28.2±2.8 ng/ml; p<0.001, respectively). Levels of F-25OH-D were higher in group A compared to both group C (5.3±0.3 pg/ml vs 3.2±0.3 pg/ml; p=0.001) and B (5.3±0.3 pg/ml vs 3.6±0.3 pg/ml; p=0.001). A significant direct correlation was found between F-25OH-D and activity index of disease (r2: 0.18; p≤0.001). A direct correlation, not reaching statistical significance, was also found between F-25OH-D and both C-reactive protein and fecal calprotectin.
Conclusions: IBD children, both at diagnosis and at follow up, have lower levels of T-25OH-D compared to healthy controls. However, among IBD patients, those at diagnosis showed higher levels of T-25OH-D and F-25OH-D than those with longer disease duration. Higher levels of both forms of Vitamin D are present in acute inflammation, suggesting that chronic inflammation is associated with a more severe deficiency of Vitamin D.