Crohn’s Disease Patients Less Able to Absorb Vitamin D, New Study Shows

Vitamin D deficiency is one well-known risk for patients with Crohn’s Disease (CD). A new study by a research team from Boston University School of Medicine (BUSM) has now demonstrated for the first time that a probable cause is a reduced ability to absorb vitamin D in quiescent CD patients. The study also demonstrated that performing a vitamin D bioavailability test on a patient is the only way to assess absorption efficiency. The findings have been made available on the website of Inflammatory Bowel Disease.

The sources of vitamin D are sunlight (ultraviolet radiation) on the skin, which causes the vitamin to be synthesized by the body, and food. In parts of the world that receive comparatively less sunlight, the population has both lower levels of hydroxyvitamin D in their bodies, and a higher incidence of inflammatory bowel disease (IBD). Beyond that, patients of all ages with IBD show a greater prevalence of vitamin D deficiency. Of IBD sufferers, it’s those with Crohn’s Disease who have the highest incidence of vitamin D deficiency.

The Boston University study looked at vitamin D absorption in 10 normal subjects (evenly divided between males and females), and 37 with quiescent CD (51% female). All received a vitamin D bioavailability test. A baseline blood sample was performed on all subjects, then a single oral capsule dose of 50,000 IU of vitamin D2 given. Twelve hours later blood was drawn to find serum D2 levels, which indicate ability to absorb the vitamin. The resulting figures showed that the Crohn’s Disease patients averaged 30% less absorption ability than the normal participants.

The findings show the importance of the oral vitamin D absorption test in evaluating a patient’s poor absorption of fat soluble vitamins. The study’s lead author, Francis Farraye, MD, MSc, professor of Medicine at BUSM, said, “We demonstrated that neither disease activity nor prior surgery or location of disease predicts the ability to absorb vitamin D.”

Senior author Michael Holick, PhD, MD, Professor of medicine, physiology and biophysics at BUSM, concurred. “Since the ability to absorb vitamin D in CD patients is unpredictable, the only way to determine absorption efficiency is to perform a vitamin D bioavailability test. This test is convenient and its use may guide clinicians in administering the appropriate therapeutic dose of vitamin D for treating vitamin D deficiency in patients with CD,” he said.

The team has also performed a pilot study using the vitamin D absorption tests on four patients with ulcerative colitis (UC). Their initial findings showed a wide range in the UC sufferers’ ability to absorb vitamin D2, similar to that in 17 CD patients. This variability in the UC patients was surprising, as vitamin D absorption takes place in the small intestine rather than the colon.

If these pilot study figures are confirmed by other researchers, a vitamin D assay may be developed as a clinical test by reference laboratories. Dr. Farraye said, “Our data support the use of an oral vitamin D absorption test in CD patients, especially in those patients who could not correct in the vitamin D deficiency by either dietary or pharmacologic means.”

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