Use of a novel vitamin D bioavailability test demonstrates that vitamin D absorption is decreased in patients with quiescent crohn's disease1,2,3

Background: Vitamin D deficiency is a common problem in patients with Crohn's disease (CD). The aim of this study was to determine the ability of normal subjects and patients with quiescent CD to absorb vitamin D2 using a novel vitamin D bioavailability test. In addition, we evaluated whether the location of disease or previous surgery had any influence on the bioavailability of vitamin D2 in CD patients. Methods: Ten normal subjects (50% female) and 37 CD patients with quiescent disease (51% female) were included in this study. Subjects who recently received any vitamin D2 were excluded. The vitamin D bioavailability test was performed in all subjects. After a baseline blood draw, all subjects were then given a single 50,000 IU oral dose of vitamin D2 in a capsule formulation and had their blood drawn 12 hours later to determine serum vitamin D2, which reflected their vitamin D2 absorption capacity. Results: Forty‐two percent and 29% of CD patients were found to be either vitamin D‐deficient (25‐hydroxyvitamin D [25(OH)D] ≤20 ng/mL] or insufficient [25(OH)D 21–29 ng/mL], respectively. Twelve hours after ingesting 50,000 IU vitamin D2, vitamin D2 levels rose from a baseline of 0.7 ± 0.7 ng/mL (mean ± SEM) to 49.8 ± 3.0 ng/mL in normal subjects. In CD patients, baseline vitamin D2 levels rose from 0 ng/mL to 34.8 ± 2.8 ng/mL. CD patients had on average a 30% decrease in their ability to absorb vitamin D2 (P = 0.01). Moreover, we found a wide variability of vitamin D2 bioavailability in CD patients. Analysis of variance (ANOVA) revealed no statistical difference of vitamin D2 bioavailability between patients in the CD subgroup stratified by the location of disease, the type of surgery, and receiving or not receiving surgery. Conclusions: More than 70% of the patients with quiescent CD were vitamin D‐deficient or insufficient. The ability to absorb vitamin D2 in CD patients is unpredictable and the only way to determine this is to perform a vitamin D bioavailability test. Use of this test may guide clinicians in administering the appropriate therapeutic dose of vitamin D for treating vitamin D deficiency in patients with CD. (Inflamm Bowel Dis 2011;)