Vitamin D is often associated with bone health, but new research suggests it may also play a role in how the immune system responds to the gut microbiome.
A study published in Cell Reports Medicine found that vitamin D supplementation was associated with changes in immune activity and gut bacteria interactions in people with inflammatory bowel disease (IBD). The findings offer insight into how diet-related factors may influence immune responses in the gut, though researchers say more evidence is needed.
The study was led by researchers at Mayo Clinic and included 48 participants with IBD who had low vitamin D levels. Participants received weekly vitamin D supplements for 12 weeks, with researchers analyzing blood and stool samples before and after the intervention.
After supplementation, researchers observed shifts in immune markers linked to how the body responds to gut bacteria. Levels of immunoglobulin A (IgA), typically associated with protective immune responses, increased, while levels of immunoglobulin G (IgG), more often linked to inflammation, decreased. The study also found changes in immune signaling pathways and increased activity of regulatory immune cells, which help control inflammation.
“This study suggests vitamin D may help rebalance how the immune system sees gut bacteria,” said lead author Dr. John Mark Gubatan, a gastroenterologist at Mayo Clinic.
Participants also showed improvements in disease activity scores and a stool-based marker of inflammation. However, the researchers emphasize that the study was small and not designed to establish cause and effect.
“We saw encouraging signals, but this was not a randomized trial,” Gubatan said. “These findings need to be confirmed in larger, controlled studies.”
IBD, which includes Crohn’s disease and ulcerative colitis, involves an abnormal immune response to bacteria that are normally harmless. Current treatments often focus on reducing inflammation but less is known about how to restore balanced interactions between the immune system and the microbiome.
The findings suggest vitamin D may be one factor that influences that balance, but they do not show that supplementation can treat or prevent IBD. Researchers caution that vitamin D use should be individualized and discussed with a health care provider, particularly for people with chronic conditions.
This study was supported by the Doris Duke Physician Scientist Fellowship Award, the Chan Zuckerberg Biohub and the National Institutes of Health.