When examining diabetes specifically, dual users again ranked highest, with a 9% elevated risk compared to non-smokers, while cigarette smokers had a 7% increase. Interestingly, but perhaps not so surprisingly, vaping alone was not significantly associated with diabetes risk. Could a factor affecting these findings be the effect of (or lack of) smoking and vaping on gut flora?
The gut–diabetes connection
Diabetes has long been linked to imbalances in gut flora, or microbiota—the complex community of bacteria in the digestive tract. When this microbial balance is disrupted, increased intestinal permeability can allow harmful bacterial products to enter the bloodstream, driving inflammation and insulin resistance. These processes are now recognized as major contributors to type 2 diabetes.
Cigarette smoking is known to alter gut flora, reducing populations of beneficial bacteria and encouraging the growth of harmful strains. These changes have been tied to higher risks of colon cancer, colitis, obesity, and diabetes. However, research to date has found no such link between vaping and gut flora disruption. A 2021 Newcastle University study reported that while smokers showed clear signs of altered gut microbiota, the microbial profile of vapers was indistinguishable from that of non-smokers.
Similarly, a mouse study examining high-fat diet–induced gut changes found that while vapour exposure increased some markers of inflammation, it did not alter microbiome composition in the way smoking does. This distinction is critical: while smoking appears to worsen gut-related pathways tied to diabetes, current evidence suggests that vaping does not exert the same effect.
Gut vs oral microbiome
Where vaping has shown measurable impact is in the mouth. A recent human study found that frequent users of electronic nicotine delivery systems (ENDS) exhibited distinct shifts in their oral bacteria, including reductions in beneficial strains and enrichment of species linked to inflammation and periodontal disease. These effects were strongest among high-intensity vapers, pointing to a potential dose-response relationship.
This suggests a nuanced picture: vaping may disrupt oral microbiota in ways that could affect periodontal health, but unlike smoking, it does not appear to damage gut flora—a key player in systemic diseases like diabetes. Then again, experts have been quick to point out that any differences in oral microbiota experienced by current vapers – most of which tend to be previous smokers – could very likely be caused by the previous smoking, in the same way that the gut microbiota can be largely affected by antibiotic intake, long after a course of antibiotics has been stopped.
Caution and context
At the same time, emerging research continues to flag areas of caution. A study in Nicotine and Tobacco Research reported that both smokers and frequent vapers who had never smoked displayed more than twice the DNA damage in oral epithelial cells compared with non-users. While, another study in Scientific Reports found that vaping was linked to changes in mitochondrial and immune response genes, biological processes closely tied to inflammation and disease.
Taken together, the evidence paints a complex picture: vaping is not entirely risk-free, but its harms appear far lower than smoking. Cigarette smoke contains more than 7,000 chemicals, dozens of which are carcinogenic and known to devastate gut and oral microbiota alike. By contrast, while e-cigarette vapour can influence oral flora and genetic pathways, it has not been shown to disrupt gut flora in ways associated with diabetes.
This context is vital. The new metabolic health study found that dual use carries the greatest risks, a pattern seen across many health outcomes. The implication is clear: encouraging complete switching away from combustible tobacco should remain the central goal of harm reduction. Misinterpreting the findings to equate vaping with smoking risks deterring smokers from making life-saving changes.
The case for harm reduction
As vaping grows in popularity worldwide, policymakers face a delicate balance. For instance, more than one in five teenagers aged 15–16 now report vaping, prompting governments like Spain’s to tighten restrictions. At the same time, these measures must avoid undermining harm reduction for adults who smoke.
The science on vapes is evolving, and studies on metabolic health, microbiota, and genetic pathways provide valuable insights. But the broader picture remains unchanged: while vaping is not harmless, it is substantially less dangerous than smoking. The key difference lies in the combustion process- responsible amongst other things – for devastating damage to the gut microbiome, and by extension, its link to diabetes.
For a tobacco harm reduction community committed to science and public health, the task is twofold: to acknowledge and study potential risks transparently, while continuing to emphasize the overwhelming evidence that smoke—not nicotine, and not vapour—is the real killer.
Study Looks Into The Relationship Between Vaping And Diabetes
