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

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 D ₂ 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 D ₂ 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 D ₂ 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 D ₂ in a capsule formulation and had their blood drawn 12 hours later to determine serum vitamin D ₂, which reflected their vitamin D ₂ 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 D ₂, vitamin D ₂ 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 D ₂ 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 D ₂ (P = 0.01). Moreover, we found a wide variability of vitamin D ₂ bioavailability in CD patients. Analysis of variance (ANOVA) revealed no statistical difference of vitamin D ₂ 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 D ₂ 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;)