Smoking helps oral bacteria settle in the gut, protecting against colitis but not Crohn’s disease. This mechanism could inspire safer treatments.
A research team led by Hiroshi ohno at the RIKEN Center for Integrative Medical Sciences (IMS) in Japan has uncovered why smoking tobacco appears to ease symptoms in people with ulcerative colitis, a chronic condition marked by inflammation in the large intestine.
Their study, published in the journal *Gut*, revealed that smoking produces certain metabolites that allow oral bacteria to establish themselves in the colon, where they activate an immune response.The findings suggest that similar benefits might be achieved through alternatives such as prebiotics like hydroquinone or probiotic treatments using bacteria such as *Streptococcus mitis*, removing the need for smoking and its well-known health risks.
Inflammatory bowel disease exists in two main forms: Crohn’s disease and ulcerative colitis. Both cause recurring abdominal pain, diarrhea, fatigue, and weight loss, but they differ in their underlying causes, the specific areas of the gut they affect, and the types of inflammation they produce.
For more than four decades, researchers have been puzzled by the paradox that smoking raises the likelihood of Crohn’s disease while simultaneously occurring offering some protection against ulcerative colitis. Because both conditions involve immune-driven inflammation in the gut, and because gut immunity is strongly shaped by the microbial community living there, Ohno and his colleagues set out to test whether the contrasting effects of smoking could be traced back to differences in gut bacteria.
Smoking changes gut bacteria
The team combined human clinical data with mouse experiments to investigate the phenomenon. In patients with ulcerative colitis, they observed that smokers had bacteria typically found in the mouth, such as *Streptococcus*, colonizing the gut-specifically in the colonic mucosa that lines the intestine. This was not the case for former smokers. Under normal conditions, oral bacteria swallowed with saliva pass through the digestive tract without establishing themselves, but smoking appeared to enable these microbes to take root in the gut mucosa.