Gastroenterology & GI Surgery

IBD and Vitamin D: Study Sheds Light on a Surprising Connection

Feb. 26, 2024 - Eden McCleskey

Optimizing IBD patients' vitamin D levels may play an important role in determining therapeutic success, according to a recent Houston Methodist study that identifies a promising new testing and treatment avenue for the complex condition.

The study, led by gastroenterologists Drs. Bincy Abraham and Christopher Fan, found that high pre-treatment vitamin D levels were associated with favorable outcomes in 88 patients taking the biologic vedolizumab for either Crohn's disease (CD) or ulcerative colitis (UC).

"Vitamin D plays a role in modulating the immune system, and prior studies have shown that a low level of vitamin D in inflammatory bowel disease patients is associated with increased disease severity and risk of treatment failure," said Dr. Abraham, director of the Fondren Inflammatory Bowel Disease Program at Houston Methodist and the study's lead author.

The study, published in the journal Nutrients, looked at whether vitamin D supplementation had an impact on vedolizumab therapy's efficacy. All patients with low pre-treatment vitamin D levels (61% of CD patients and 47% of UC patients) were put on vitamin D supplements upon initiating treatment with vedolizumab. Patients with normal pre-treatment vitamin D levels were not supplemented.

Higher vitamin D levels were observed after treatment in both UC and CD patients, and improvements in the clinical activity scores and endoscopic scores of both groups were consistent with the known efficacy of vedolizumab.

For patients with high levels of C-reactive protein — or a higher burden of disease — a drop in CRP levels corresponded directly with a rise in vitamin D levels, indicating that there was a possible connection between the supplementation of vitamin D and their improved clinical outcomes. Interestingly, this correlation was only statistically significant among patients with CD.

"Ulcerative colitis is more limited to the colon, whereas Crohn's disease can involve the entire GI tract," explained Dr. Fan, the Fondren Centennial Chair in Gastrointestinal Microbiome at Houston Methodist. "Vitamin D is absorbed higher up in the digestive tract, in the small bowel, which is probably why fewer patients with UC had low pre-treatment vitamin D levels and why the correlation between vitamin D and inflammation wasn't pronounced as it was in CD."

Given the essential role of the small bowel in nutrient assimilation, CD patients may exhibit greater susceptibility to alterations in vitamin D levels, thereby influencing treatment efficacy.

Vedolizumab, a gut-specific drug known for its limited systemic side effect profile, has emerged in the past decade as a prominent treatment for both ulcerative colitis and Crohn's disease. Although this study focused exclusively on patients taking vedolizumab, the researchers believe the findings would likely extend to most — if not all — biologic drug formulations used to treat IBD.

For that reason, Dr. Abraham stressed the importance of integrating vitamin D evaluation and optimization into routine care protocols, urging fellow practitioners to recognize the multifaceted significance of vitamin D in immune modulation and bone health, beyond its traditional association with nutritional deficiencies.

"Gastroenterologists aren't used to looking at vitamin D levels; they are typically more worried about iron deficiency anemia and vitamin B12 deficiency, because inflammatory bowel disease patients have bleeding, and patients with Crohn's disease have trouble absorbing vitamin B12," said Dr. Abraham, a national IBD expert.

On top of that, vitamin D deficiency is a global phenomenon, affecting large swaths of the population, and for most people, its effects are minor and difficult to define.

"With this study, we're trying to raise awareness that vitamin D deficiency is more serious for people with inflammatory bowel disease, but luckily, this one relatively simple step of adding supplementation to their routine can have a really big impact on their health," concluded Dr. Fan.

By embracing the role of vitamin D alongside established therapeutic modalities, gastroenterologists can chart a course towards improved outcomes and enhanced quality of life for patients with inflammatory bowel disease.

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