BACKGROUND/AIMS The exact relationship between vitamin D deficiency and inflammatory bowel disease (IBD) remains unclear. We evaluated the effect of vitamin D3 administration on inflammatory responses and disease severity in patients with IBD.

METHODS We investigated the serum 25-hydroxyvitamin D3 [25-(OH)D] and C-reactive protein (CRP) levels and the partial Mayo score (PMS) in patients with IBD. Vitamin D3 was administered in patients with either vitamin D deficiency or insufficiency and CRP serum vitamin D levels and PMS were re-examined at 6 months of administration.

RESULTS In 88 patients with Crohn's disease (CD), a negative correlation was found between serum vitamin D and CRP. In 178 patients with ulcerative colitis (UC), serum vitamin D showed no association with CRP or PMS. Serum vitamin D increased from 11.08±3.63 to 22.69±6.11 ng/mL in 29 patients with CD and from 11.45±4.10 to 24.20±6.61 ng/mL in 41 patients with UC who received vitamin D3 treatment (P<0.001 and P<0.001, respectively). In patients with CD, median ΔCRP was -0.24 in the normalized vitamin D group and -0.11 in the non-normalized group (P=0.308). In patients with UC, median ΔCRP was -0.01 in the normalized vitamin D group and 0.06 in the non-normalized group (P=0.359).

CONCLUSIONS Although a negative correlation was found between serum vitamin D and CRP levels in patients with CD, administration of vitamin D did not improve the CRP level in patients with CD. In patients with UC, serum vitamin D level was unrelated to CRP or PMS.