Smoking Increases Risk of All Subtypes Type 2 Diabetes

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Individuals with any history of smoking have a substantially higher risk of all 4 subtypes of type 2 diabetes (T2D) compared to those who have never smoked, according to data presented at the European Association for the Study of Diabetes.1

Conducted in Stockholm, Sweden by Emmy Keysendal, a PhD candidate at Karolinska Institute, this trial compared smoking status across the previously defined 4 subcategories of T2D. These categories include:

  • Severe insulin-resistant diabetes (SIRD), characterized by insulin resistance,
  • Severe insulin-deficient diabetes (SIDD), characterized by a lack of insulin,
  • Mild obesity-related diabetes (MOD), associated with obesity and younger onset age, and
  • Mild age-related diabetes (MARD), which develops later in life.1

The team collected data on 3325 individuals with T2D – 495 were categorized as SIDD, 477 as SIRD, 693 as MOD, and 1660 as MARD. An additional 3897 participants were included as controls. All data was sourced from the long-running HUNT diabetes study in Norway, wherein patients exhibited an average follow-up time of 17 years, and the ESTRID case-control study in Sweden.1

Based on these data, patients who had smoked at any point in their lives were 2.15 times more likely as those who had never smoked to develop SIRD (95% CI, 1.64-2.82). A 20% increase was found for SIDD (risk ratio [RR], 1.2; 95% CI, 0.98-1.47), 29% for MOD (RR, 1.29; 95% CI, 1.06-1.57), and 27% (RR, 1.27; 95% CI, 1.12-1.44) for MARD. It was also determined to be responsible for >1/3 of SIRD cases, but <15% of the other subcategories.2

Smoking heavily – defined as 20 cigarettes a day for 15 years or equivalent – increased the risk of all 4 subtypes. Heavy smokers were 2.35 times more likely to develop SIRD (RR, 2.35; 95% CI, 1.72-3.23), SIDD (RR, 1.52; 95% CI, 1.19-1.95), MOD (RR, 1.57; 95% CI, 1.22-2.02) and MARD (RR, 1.45; 95% CI, 1.22-1.69). Additionally, heavy smokers with a predisposition to T2D or reduced insulin secretion were particularly vulnerable.2

The association between smoking and all T2D subtypes was then confirmed by the MR study (odds ratios [ORs] SIDD, 1.49; 95% CI, 1.05-2.12; SIRD, 1.55; 95% CI, 1.10-2.19; MOD, 1.52; 95% CI, 1.09-2.11; MARD, 1.26; 95% CI, 0.96-1.64).2

Ultimately, investigators noted a higher risk of T2D across all subtypes due to heavy smoking, with a stronger association for SIRD. This indicates a negative effect of smoking on insulin sensitivity.2

“These findings underscore the importance of refraining from smoking in the prevention of T2D,” wrote Keysendal and colleagues.2

References
  1. European Association for the Study of Diabetes. Smoking increases the risk of type 2 diabetes, regardless of its characteristics. Eurekalert! September 13, 2025. Accessed September 13, 2025. https://www.eurekalert.org/news-releases/1097810
  2. Keysendal E, Ahlqvist E, Åsvold B, et al. Tobacco Use, Genetic Susceptibility, and the Risk of Type 2 Diabetes Subtypes. Abstract presented at the European Association for the Study of Diabetes in Vienna, Austria, September 15-19.

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