Vitamin D deficiency in inflammatory bowel disease: prevalence and predictors in a Norwegian outpatient population

Background and aim: Vitamin D deficiency is common in inflammatory bowel disease (IBD). The aims of the present study were to determine the prevalence of vitamin D deficiency and to identify clinical and epidemiological variables associated with vitamin D deficiency in an outpatient population with IBD. Methods: Participants were recruited from nine hospitals in the southeastern and western regions of Norway as part of an observational, multicentre study from March 2013 to April 2014. Clinical and epidemiological data were collected by interview and from medical records. All analyses of serum 25-hydroxyvitamin D (25-OH-D) were performed in the same laboratory. Results: In total, 49% (200/408) of the patients had a 25-OH-D concentration <50 nmol/L, including 53% (122/230) of the Crohn's disease (CD) patients and 44% (78/178) of the ulcerative colitis (UC) patients. In CD patients, disease activity, measured as the HBI, was inversely associated with vitamin D deficiency. No such association was observed with the Simple Clinical Colitis Activity Index (SCCAI) scores in UC, but in UC patients, vitamin D deficiency was associated with elevated faecal calprotectin >100 mg/kg. In patients with CD, there were significantly more relapses during the previous year in patients with vitamin D deficiency. Conclusions: Vitamin D deficiency was common, especially in CD, and was associated with increased disease activity, a relapsing disease course and higher inflammatory activity.