Did you know that smoking, in addition to damaging lungs and the cardiovascular system, also harms the gut microbiome? The microbiome, the complex ecosystem of microbes living in your gut and influencing many disease states including diabetes, dementia and Inflammatory Bowel Disease, is damaged by the chemicals in cigarette smoke. In a healthy individual, the gut microbiome typically consists of the Firmicutes and Bacteroides phyla (involved in carbohydrate utilisation), with minor representations from the Proteobacteria (involved in oxygen uptake) and Actinobacteria phyla (involved in immune responses and gut permeability). However, a study by Yoon (2020) found that smokers had decreased levels of Actinobacteria, Proteobacteria and Firmicutes but increased levels of Bacteriodetes, resulting in gut microbiome dysbiosis.
Such dysbiosis can cause an impaired regulation of digestion (e.g. extraction, synthesis, and absorption of nutrients and metabolites), immune function (e.g. inhibition of pathogen colonisation, innate and adaptive immune cells function regulation and maintenance of the intestinal epithelium integrity), development, and homeostasis. Hence, beyond the direct toxicity of the harmful constituents of cigarette smoke on multiple organ systems, smoking’s harmful effects may also be mediated in part through the gut microbiome.
Interestingly, the use of e-cigarettes seemed to have a lesser impact on the gut microbial profiles although this is based only on a single small study. In a study by Stewart et al (2018), ten e-cigarette users with at least 3 years of vaping history, ten tobacco smokers who smoked at least 10 cigarettes per day and ten controls with no smoking history had Prevotella and Bacteroides levels in their faecal samples measured. In the smokers’ cohort, significant increase and reduction in Prevotella and Bacteroides were observed, respectively. However, there were no significant changes in the gut microbial diversity observed in the e-cigarette cohort compared to the non-smokers.
Whilst heated tobacco products, or specifically IQOS manufactured by Philip Morris, is deemed by the US FDA to have ‘reduced exposure’, there is no published literature to the best of our knowledge on the effect of heated tobacco products on the gut microbiome. This would be important to study as the FDA acknowledged that the IQOS system significantly reduces the production of harmful and potentially harmful chemicals and that “switching completely from conventional cigarettes to the IQOS system significantly reduces your body’s exposure to harmful or potentially harmful chemicals”.
Given the growing realization of the importance of the gut microbiome to human health and louder and louder advocacy to switch smokers who cannot or will not stop smoking to e-cigarettes or heated tobacco products (the so-called ‘tobacco harm reduction strategy’), it is important that more independent research is conducted on the effects of these smoking alternatives on the gut microbiome.
Finally, one non-obvious gut-related risk of smoking: smokers have an 80% higher risk of Clostridium difficile infection, a disease that affects half a million Americans annually and causes 29,000 deaths per year. Why? 90% of cigarettes contain Clostridium bacteria species which are introduced into the gut through repeated smoking. Another risk that needs to be reduced!
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About the authors
Lim Shu Han is a Biomedical Science student from Temasek Polytechnic. She is currently interning at AMILI.
Dr Jeremy Lim is the co-founder and CEO of AMILI.