Tobacco could impair the microbial diversity of the small intestine

The intestinal flora of smokers is less rich and less diversified than that of non-smokers. This difference is likely to encourage the development of gastrointestinal diseases, according to Australian researchers who have conducted the very first study on the harmful effect of tobacco on the duodenal microbiota.


Tobacco triggers and exacerbates numerous gastrointestinal diseases such as inflammatory bowel diseases, ulcers caused by infection, and gastrointestinal cancers. It is thought to promote the appearance of these disorders by impairing the balance of the intestinal microbiota, particularly in the first part of the small intestine–or duodenum. To study its impact, a group of scientists analyzed the bacterial composition of the small intestine based on samples of intestinal mucosa obtained from 102 participants, including 20 individuals suffering from Crohn’s disease. The other volunteers suffered from gastrointestinal pain at the time of the study. Of these, 21 were daily smokers, 40 were former smokers and 41 had never smoked.

A depleted microbiota

From this analysis it emerged that cigarettes disrupted the equilibrium of the duodenal microbiota and reduced the number of species present without reducing their total mass. The bacterial diversity of smokers was lower than that of non-smokers. However, the scientific literature is adamant:a varied gastrointestinal microbiota is a guarantee of gastrointestinal health. The microbiota of former smokers was also less diversified than that of non-smokers, but the authors emphasize that “they represent an intermediate condition between daily smokers and individuals who have never smoked”. And furthermore: “this suggests that quitting smoking may induce a rapid return to microbial balance”.

Mechanisms to be clarified

The researchers believe that cigarettes could impair microbial diversity by acting on the immune system, by affecting the bacteria directly or by reducing the oxygen level in the intestines. These different mechanisms of action might also lead to the selection of certain groups of bacteria that contribute to the development of gastrointestinal diseases. To find out more, the authors suggest carrying out other larger scale studies on the duodenum that take smoking into account as a factor than can disrupt the results.



Shanahan et al. Influence of cigarette smoking on the human duodenal mucosa-associated microbiota, Microbiome (2018)