A study analyzing data from more than 3,300 individuals diagnosed with type 2 diabetes and nearly 3,900 participants without the condition has confirmed smoking as a significant risk factor across every subtype of the disease. The research, conducted at the Institute of Environmental Medicine at Karolinska Institutet in Sweden, found that people who had ever smoked faced elevated odds of developing type 2 diabetes regardless of which form of the condition they developed.
Current and former smokers were found to have doubled their risk of developing severe insulin-resistant diabetes compared to people who had never smoked. Across the other subtypes, people who had ever smoked saw their risk for severe insulin-deficient diabetes rise by 20%, mild age-related type 2 diabetes by 27% and mild obesity-related type 2 diabetes by 29%.
How type 2 diabetes was categorized
The study divided type 2 diabetes into four distinct subtypes based on factors including age, insulin resistance and obesity. Those categories were mild age-related diabetes, mild obesity-related diabetes, severe insulin-deficient diabetes and severe insulin-resistant diabetes. Researchers structured the analysis this way to determine whether smoking affected all subtypes equally or whether certain groups faced disproportionately higher risks.
Emmy Keysendal, a PhD student leading the research, said the findings support the case for treating smoking cessation as a prevention tool across all forms of the condition rather than limiting concern to any single subtype.
Heavy smokers face the steepest odds
The risks were most pronounced among heavy smokers, defined in the study as people who smoked approximately 20 cigarettes a day over 15 years. That group faced 2.35 times the likelihood of developing severe insulin-resistant diabetes compared to nonsmokers. Their risk for mild obesity-related diabetes was 57% higher, severe insulin-deficient diabetes was 52% higher and mild age-related diabetes was 45% higher.
Smokeless tobacco carries risk too
The study also examined smokeless tobacco products, including snus, a form of tobacco widely used in Scandinavia. People who used these products faced a 19% higher chance of developing severe insulin-deficient diabetes and a 13% higher risk for severe insulin-resistant diabetes. Although smokeless tobacco does not involve combustion and generally contains fewer harmful byproducts than cigarettes, it still delivers nicotine, which researchers believe may contribute to insulin resistance.
Vaping and nicotine pouches raise similar concerns
As vaping and nicotine pouches have grown in popularity, the research raises questions about whether these products carry comparable risks despite being widely marketed as safer alternatives. Keysendal noted that both products still deliver high concentrations of nicotine, which may elevate diabetes risk through similar biological pathways as traditional tobacco.
A broader picture of risk
Family medicine physician David Cutler, commenting on the study’s implications, noted that smoking has sometimes been incorrectly associated with appetite suppression and weight control, leading to a mistaken assumption that it might reduce diabetes risk. The data contradicts that idea directly. Cutler also pointed to the value of studying non-smoking contributors to diabetes risk, including diet, physical activity and genetic factors, as part of a fuller picture of who is most vulnerable and why.
The findings arrive as type 2 diabetes continues to affect a growing share of the population, with rates rising across age groups and demographics. Public health researchers say the data reinforces the case for incorporating smoking cessation into diabetes prevention strategies, particularly for communities that face higher baseline rates of the disease.
