Scientists have suggested that inflammatory bowel disease (IBD), a painful condition triggering the immune system to mistakenly attack healthy bowel cells, and can cause ulcerative colitis and Crohn’s disease, might be relieved by vitamin D supplementation, reports MedicalNewsToday.
Their recent study published in Cell Reports Medicine examined how vitamin D may affect sufferers, and that boosting supplementation levels may help the body’s immune system tolerate gut bacteria.
The study involved 48 adults who either had ulcerative colitis or Crohn’s disease, as well as low vitamin D levels. Researchers collected blood and stool samples from participants at baseline and then again at after 12 weeks. Over these 12 weeks, participants received weekly doses of vitamin D.
A number of components were examined, 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.
The team also looked at two critical types of immunoglobins: IgA and IgG, which are specific proteins produced by certain white blood cells. IgA performs several helpful functions in the digestive system, including regulating gut bacteria.
The study team found that vitamin D had several positive effects on participants: that it 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 vitamin D supplementation resulted in improvement of the patients as measured by disease activity scores as well as markers of inflammation – and resulted in significant changes in the intestinal microbial composition that were beneficial as well as in the gut immune system,” said 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.
Cristiano Pagnini, MD, PhD, consultant gastroenterologist and researcher at San Giovanni Addolorata Hospital in Rome, who was also not involved, said 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 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 MedicalNewsToday.
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
This study was relatively small and did not provide long-term data; thus, larger, longer-term studies will be helpful as research moves forward.
The researchers also acknowledge that giving vitamin D wasn’t based on a randomised process or compared to a placebo.
Pagnini underscored that caution was warranted and that the study’s clinical endpoints were exploratory. “Only serum vitamin D level is considered, while Vitamin D receptor (VDR) expression and activation are not investigated,” he said.
He pointed out that the findings may be optimistically over-interpreted and that larger, controlled studies are needed.
“While the biological signals are strong, they do not yet translate into clear evidence of clinical benefit. As is often the case with sophisticated multi-omics research, there is a risk that mechanistic insights may be overinterpreted when applied to patient care,” he added.
John Gubatan, MD, study author and gastroenterologist at Mayo Clinic in Florida, said the next steps in research would need to explain the biological mechanism behind how vitamin D behaves in the GI tract, as well as address questions such as how much vitamin D IBD patients need.
“Our exploratory study highlights [that] there could be potential benefits with vitamin D in controlling the interactions between the immune system and gut microbiome in patients with IBD and that further work is needed to understand the exact vitamin D levels and vitamin D supplementation strategies to support this in patients with IBD and other chronic inflammatory diseases,” he said.
“As a next step, we are hoping to better understand if some of the gut bacteria promoted by vitamin D could be used to directly to improve IBD and understand how this works from an immune landscape standpoint.
“We also hope to better understand how some of the B and T regulatory cells (immune cells that control inflammation) that migrate to the gastrointestinal tract increased by vitamin D in this study are helpful in patients with IBD,” he added.
Cohn said the implications of this study for care of patients with IBD are significant, but that more research were needed before making widespread recommendations.
“Further studies of vitamin D supplementation on different disease subgroups and its interaction with specific therapeutic agents are needed to help clarify where supplementation with Vitamin D fits into current therapeutic approaches to treating patients with IBD,” he said.
Gubatan noted that current guidelines on vitamin D supplementation were based on bone health and calcium metabolism.
“Patients with chronic inflammation may have different vitamin D needs. Those who are vitamin D-deficient should discuss supplementation with their providers and have levels rechecked as per current guidelines. It’s too early to recommend measuring gut microbiome or immune markers to test vitamin D efficacy,” he said
Study details
Multi-omics reveal vitamin D regulation of immune-gut microbiome interactions and tolerogenic pathways in inflammatory bowel disease
John Gubatan, Raoul Sojwal, Jiayu Ye et al.
Published in Cell Reports Medicine on 26 March 2026
Summary
Loss of immune tolerance to the gut microbiome plays a pathogenic role in inflammatory bowel disease (IBD). How dietary factors alter host immune-gut microbiome interactions in IBD is unclear. Here, we apply multi-omics (immunoglobulin A or G and 16S rRNA sequencing [IgA-seq, IgG-seq], blood single-cell RNA sequencing [scRNA-seq], and immune repertoire sequencing) to investigate the effects of 12 weeks of vitamin D on host immune microbe interactions in patients with IBD. Vitamin D treatment associates with decreased disease activity and inflammatory markers and increased IgA-bound and decreased IgG-bound gut microbiota. Vitamin D alters the profiles of IgA-bound (increased Lachnospiraceae, Blautia) and IgG-bound (decreased Proteobacteria, Enterococcaceae) gut bacteria. Vitamin D increases B cell activating factor (BAFF) signaling between plasmacytoid dendritic cells and B cells, alters BCR and TCR clonotypes that associate with Ig-bound gut microbiota, and increases α4β7+ B and T regulatory cells. Our results demonstrate that vitamin D promotes immune tolerance to gut microbiota in patients with IBD.
See more from MedicalBrief archives:
People with IBD have elevated risk of heart attack
Can inflammatory bowel disease be treated with diet?
Landmark finding on cause of inflammatory bowel disease and immune disorders