How does oral microbial diversity in Crohn's disease compare to people without the condition?
Crohn's disease (CD) is a type of inflammatory bowel disease (IBD) that can affect the entire digestive tract, including the mouth. Researchers have found that the community of bacteria living in the mouth — the oral microbiome — is different in people with CD compared to those without the condition. A large meta-analysis of 25 studies confirmed that oral microbial diversity is significantly reduced in CD, meaning there are fewer types of bacteria present. This change may be linked to inflammation and could offer clues about the disease.
What the research says
A comprehensive meta-analysis of 25 studies (1,136 IBD patients and 759 controls) found that oral microbial Shannon diversity — a measure of how many different species are present and how evenly they are distributed — is significantly lower in people with IBD compared to healthy controls 7. The reduction was driven primarily by Crohn's disease, with a standardized mean difference of -0.372 (p < 0.001) 7. This means the difference is moderate and unlikely to be due to chance. In contrast, people with ulcerative colitis showed less divergence from controls 7.
Beyond diversity, the types of bacteria also differ. The meta-analysis identified specific bacteria that are more common in CD, such as Corynebacterium, Serratia, and Streptococcus, while bacteria like Porphyromonas and Ruminococcaceae were more common in healthy controls 7. These shifts suggest that the oral environment in CD favors certain microbes over others.
Functional predictions from the same study indicated that the oral microbiome in CD has reduced capacity for butyrate metabolism — butyrate is a short-chain fatty acid that helps reduce inflammation and maintain gut health 7. This aligns with findings from a separate review that protective microbial metabolites like short-chain fatty acids are decreased in IBD 2.
An earlier study using a specialized microarray technique also found significantly lower microbial diversity in tongue samples from children with CD compared to healthy controls, with notable decreases in Fusobacteria and Firmicutes bacteria 9. This supports the meta-analysis results and shows the effect is present even in younger patients.
What to ask your doctor
- Could changes in my oral microbiome be related to my Crohn's disease activity or symptoms?
- Are there any tests available to check my oral or gut microbiome, and would the results help guide my treatment?
- Should I consider any specific oral hygiene practices or dietary changes to support a healthier microbiome?
- How do my current medications (e.g., biologics, immunosuppressants) affect my oral and gut bacteria?
- Is there any ongoing research on oral microbiome-based therapies for Crohn's disease that I might be eligible for?
This question is drawn from common patient questions about Gastroenterology and answered using cited medical research. We do not provide individualized advice.