Smoking significantly raises the risk of developing type 2 diabetes across all subtypes, according to new research presented at the European Association for the Study of Diabetes (EASD) annual meeting in Vienna.
Researchers from Sweden, Norway, and Finland found that current and former smokers were more likely to develop every subtype of type 2 diabetes. This includes every subtype of the disease. The strongest association was seen for severe insulin-resistant diabetes (SIRD), where smoking appeared to more than double the risk.
Understanding Diabetes Subtypes
Type 2 diabetes (T2D) affects millions worldwide and is known for its complexity and variability. Previous research has proposed that it can be divided into four subtypes:
- SIRD (severe insulin-resistant diabetes): marked by the body’s inability to respond properly to insulin.
- SIDD (severe insulin-deficient diabetes): driven by inadequate insulin production.
- MOD (mild obesity-related diabetes): linked to obesity and younger onset.
- MARD (mild age-related diabetes): typically developing later in life.
These subtypes differ in severity, prognosis, and risk of complications. Until now, it was unclear whether risk factors like smoking impacted them differently.
The Study
The research team was led by PhD student Emmy Keysendal from Karolinska Institutet in Stockholm. They examined long-term data from Norway and Sweden. They analysed 3,325 people with type 2 diabetes. The researchers also analysed 3,897 controls, using data from a 17-year follow-up study. This included a case-control study.
Results showed that “ever smokers” – including current and past smokers – faced a higher risk of all four diabetes subtypes. This risk was higher compared with non-smokers.
The link was particularly strong for SIRD. Smokers were 2.15 times more likely to develop this form of diabetes. This is compared with increases of 20% for SIDD. There is a 29% increase for MOD and a 27% increase for MARD.
Heavy Smoking and Snus Use
Heavy smokers are defined as those consuming at least 20 cigarettes daily for 15 years or the equivalent. They faced even greater risks. They were:
- 2.35 times more likely to develop SIRD.
- 52% more likely to develop SIDD.
- 57% more likely to develop MOD.
- 45% more likely to develop MARD.
In Sweden, heavy use of snus is linked to higher risks of severe diabetes subtypes. This smokeless tobacco product poses additional health concerns. Men who used snus heavily were 19% more likely to develop SIDD and 13% more likely to develop SIRD compared with non-users.
The Role of Genetics
The researchers also examined how smoking interacts with genetic risk factors. They found that people with a genetic predisposition to diabetes, insulin resistance, or reduced insulin secretion were particularly vulnerable to smoking’s harmful effects.
For example, heavy smokers with high genetic risk for impaired insulin secretion had more than three times the risk of developing SIRD compared with those without these risk factors.
Implications for Prevention
The study’s findings highlight smoking as a major preventable risk factor for all forms of type 2 diabetes.
“It is clear that smoking increases the risk of type 2 diabetes whatever the subtype,” said Ms Keysendal. “The strongest association was seen for severe insulin-resistant diabetes, which suggests smoking may contribute to diabetes by impairing the body’s ability to respond to insulin.”
She added that genetic information could help identify people who might benefit most from targeted support to quit smoking.
A Call for Action
The research underscores the importance of smoking cessation programs not just for cardiovascular and respiratory health, but also for diabetes prevention.
Experts stress that reducing tobacco use could prevent thousands of cases of type 2 diabetes worldwide, particularly among genetically vulnerable individuals.
As Ms Keysendal concluded: “Our findings emphasise the importance of smoking cessation in the prevention of type 2 diabetes. They also indicate that genetic information may help identify individuals most likely to benefit from extra support in stopping smoking.”