BackgroundAlthough the pathogenesis of osteopenia in Crohn’s disease is not established, vitamin D deficiency is thought to be an important risk factor. However, little is known about the prevalence of vitamin D deficiency in patients with Crohn’s disease in Japan. This study aimed to clarify the prevalence of vitamin D deficiency in patients with Crohn’s disease in Japan and to examine the possible causes of the deficiency.MethodsWe investigated serum 25-hydroxyvitamin D (25-OHD) levels, various laboratory parameters, and patient histories in 33 outpatients (25 men, 8 women; median age, 37 years; range, 26–57 years) and 15 age- and sex-matched healthy controls (8 men, 7 women; median age, 37 years; range, 24–57 years) and assessed risk factors for vitamin D deficiency.ResultsAlthough patients with Crohn’s disease did not have significantly lower serum concentrations of 25-OHD than controls, 9 of 33 patients (27.3%) were considered vitamin D deficient (serum 25-OHD level ≤10 ng/ml) compared with only 1 of 15 (6.7%) controls. Serum 25-OHD levels were significantly related to disease duration (r = 0.46, P = 0.003), Crohn’s Disease Activity Index (CDAI) score (r = 0.44, P = 0.005), International Organization for the Study of Inflammatory Bowel Disease score (r = 0.30, P < 0.05), and serum values of ferritin (r = 0.34, P = 0.03), C-reactive protein (r = 0.34, P = 0.03), total cholesterol (r = 0.31, P = 0.04), and intact parathyroid hormone (r = 0.23, P < 0.05). A logistic regression analysis was performed to investigate the ability of variables to predict low or normal 25-OHD values. Results showed that disease duration (P = 0.03) and CDAI score (P = 0.04) could predict the occurrence of vitamin D deficiency (r2 = 0.472, P = 0.0004).ConclusionsVitamin D deficiency exists in patients with Crohn’s disease in Japan. 25-OHD levels should be assessed in patients who have had Crohn’s disease for a long time (>15 years) and who have been in the active stage of the disease for long periods.