IBD: Vitamin D may stop immune system from attacking gut bacteria - Medical News Today

- Inflammatory bowel disease is a chronic condition where the body’s immune system attacks the intestines.

- Research is ongoing on the best ways to manage inflammatory bowel disease, including through medication and lifestyle changes.

- Results from a small study suggest that taking vitamin D may be helpful for people with inflammatory bowel disease and may help the body avoid attacking itself.

Inflammatory bowel disease (IBD) is a condition that “triggers the body’s immune system to mistakenly attack healthy bowel cells,” leading to symptoms such as persistent fatigue, abdominal pain, chronic diarrhea, and unexplained weight loss, according to the Centers for Disease Control and Prevention.

IBD includes the subtypes of ulcerative colitis and Crohn’s disease, and people with IBD can experience flare-ups of such symptoms intermittently.

A recent study published in Cell Reports Medicine examined how vitamin D supplementation may affect people with IBD, and found that increasing vitamin D levels may help the body’s immune system tolerate gut bacteria.

Vitamin D and how the body responds to gut bacteria

This study involved 48 adult participants who either had ulcerative colitis or Crohn’s disease and also had low vitamin D levels. Researchers collected blood and stool samples from participants at baseline and then again at the end of twelve weeks. Over these 12 weeks, participants received weekly doses of vitamin D.

Researchers evaluated a number of components, including disease activity, quality of life, and C-reactive protein in blood and stool samples. C-reactive protein can help with measuring inflammation in the body.

Researchers also focused on looking at two critical types of immunoglobins: IgA and IgG. Immunoglobulins are specific proteins produced by certain white blood cells. IgA performs several helpful functions in the digestive system, including regulating gut bacteria.

Researchers found that vitamin D had several positive effects on participants. They saw that vitamin D helped “reset” and “rebalance” the immune system’s communication with the gut microbiome. The researchers described this as promoting immune tolerance, rather than just suppressing inflammation.

Vitamin D supplementation also helped increase IgA levels, which are linked to a more stable immune response, and lower Immunoglobulin G (IgG) levels, which are linked to pro-inflammatory responses in the gut.

After 12 weeks, participants also had lower disease activity scores, meaning they felt better overall and clinically had fewer or less severe symptoms. The researchers also observed a decrease in stool-based markers of inflammation.

How does vitamin D achieve this effect?

“The study showed that vitamin D supplementation for 12 weeks resulted in improvement of the patients as measured by disease activity scores as well as markers of inflammation. Supplementation with vitamin D resulted in significant changes in the intestinal microbial composition that were likely beneficial as well as in the gut immune system,” Steven Cohn, MD, PhD, AGAF, FACG, chief of the Division of Gastroenterology and Hepatology at the University of Texas Medical Branch, who was not involved in the study, said.

Cristiano Pagnini, MD, PhD, consultant gastroenterologist and researcher at San Giovanni Addolorata Hospital in Rome, Italy, who was also not involved in the study, explained that the findings suggest that vitamin D may influence how the immune system interacts with the gut microbiome in IBD.

“By combining microbiome and immune profiling, the authors suggest that vitamin D supplementation could shift the balance from a more inflammatory IgG-driven response toward a more tolerogenic IgA-mediated one. This is an appealing concept, as it frames IBD not just as excessive inflammation, but as a failure of immune tolerance to gut bacteria,” he told Medical News Today.

Pagnini added that the study sheds light on mechanisms of potential interactions between the vitamin D pathway and microbiota composition, which aligns with recent hypotheses of a reciprocal, synergistic effect between vitamin D supplements and probiotics.

Study limitations and what’s next in research

This study was relatively small and did not provide long-term data; thus, larger, longer-term studies will likely be helpful as research moves forward.