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P331. Total, free and bioavailable 25(OH) vitamin D inversely correlate with faecal calprotectin in patients with inflammatory bowel disease

M. Garg1, O. Rosella2, J. Lubel1, P. Gibson2, 1Monash University, Gastroenterology, Eastern Health, Box Hill, Australia, 2Monash University, Gastroenterology, The Alfred Hospital, Prahran, Australia

Background

The relationships of objective markers of disease activity with circulating total, free and bioavailable 25(OH) vitamin D (25(OH)D), and of vitamin D binding protein (DBP) are unknown.

Aim: To measure circulating levels of the key components of the vitamin D axis in patients with IBD and in healthy controls, and to correlate these with markers of disease activity.

Methods

Healthy controls (HC), and patients with Crohn's disease (CD) and ulcerative colitis (UC) attending Eastern Health IBD Clinics were recruited, and demographic and clinical data recorded. Blood samples were analysed for 25(OH)D by chemiluminescence, and in a subgroup DBP by ELISA. Systemic inflammation was assessed via the serum C-reactive protein (CRP) and intestinal inflammation via faecal calprotectin (FC).

Results

21 HC (12 female; mean age 37, range 23–68 y), 37 patients with CD (17 female; aged 41, 23–76 y) and 31 with UC (14 female; aged 45, 22–82 y) were studied. No significant demographic differences were noted between the groups. Serum 25(OH)D concentration was similar across all 3 groups (mean 70 nmol/L in patients with CD, 69 nmol/L in patients with UC and 67 nmol/L in HC, p = NS). A significant inverse correlation between 25(OH)D and log calprotectin (log FC) was noted in patients with CD (Pearson r = −0.38, p = 0.033), UC (r = −0.39, p = 0.039) and all patients with IBD (r = −0.39, p = 0.003). No correlation with CRP was noted. 34 of the 68 patients with IBD were taking vitamin D supplements; in these patients, a significant inverse correlation between 25(OH)D and log FC was also noted (r = −0.50, p = 0.006). The inverse correlation was also noted amongst patients with only colonic CD or UC (r = −0.36, p = 0.031). There was no significant difference in sunlight exposure between groups. In a subgroup of 20 HC, 20 patients with CD and 15 patients with UC, DBP was similar across the 3 groups, as were calculated free and bioavailable 25(OH)D. Free and bioavailable 25(OH)D significantly correlated with log FC in the IBD group as a whole or with CD and UC alone, whereas DBP did not.

Conclusion

Despite total, free and bioavailable 25(OH)D concentrations being similar to those in a healthy control population, they inversely correlate with the degree of intestinal inflammation. This association is not influenced by malabsorption or variations of sunlight exposure; and hence provides further evidence that vitamin D may play an immunomodulatory role in IBD. Studies are required at the intestinal level.