It's not just cancer: Smoking may trigger all types of type-2 diabetes

From insulin resistance to insulin deficiency, smoking raises the risk of every type-2 diabetes form - and the more you smoke, the worse it gets, says new study

Far beyond its well-known impact on cancer and heart disease, smoking has now been linked to every form of type-2 diabetes.

A new study titled Smoking increases the risk of type 2 diabetes, regardless of its characteristics, presented at the ongoing European Association for the Study of Diabetes (EASD) 2025 conference in Vienna (September 15–19), reveals that smoking increases the likelihood of developing all four subtypes of type-2 diabetes.

 

Researchers from Sweden, Norway, and Finland found that whether diabetes is driven by insulin resistance, insulin deficiency, obesity, or age, smoking worsens the risk. The strongest association was with severe insulin-resistant diabetes (SIRD) — a particularly aggressive subtype.

What are the subtypes of type-2 diabetes?

Traditionally, type-2 diabetes has been viewed as a single disease. But researchers now classify it into four distinct subtypes:

• SIRD (Severe Insulin-Resistant Diabetes): When the body’s cells stop responding to insulin, leaving glucose levels high 
• SIDD (Severe Insulin-Deficient Diabetes): Characterised by low insulin production 
• MOD (Mild Obesity-Related Diabetes): Linked to obesity, often developing at a younger age 
• MARD (Mild Age-Related Diabetes): Occurs later in life, with slower progression 

These subtypes differ in severity, complications, and treatment needs — but this study shows smoking cuts across them all.

How much does smoking raise the risk of each diabetes subtype?

The researchers analysed data from 3,325 people with diabetes and 3,897 people without diabetes from large-scale Scandinavian health studies. Here’s what they found:

• SIRD: Smokers were 2.15 times more likely to develop this severe subtype than non-smokers 
• SIDD: Risk increased by 20 per cent 
• MOD: Risk increased by 29 per cent 
• MARD: Risk increased by 27 per cent

 

Among heavy smokers (15+ pack-years or about one pack a day for 15 years), the risks were even higher:

• SIRD: 2.35 times higher risk
• SIDD: 52 per cent higher 
• MOD: 57 per cent higher 
• MARD: 45 per cent higher

Does smokeless tobacco carry similar risks?

The study found that, in Sweden, men who used snus (a popular smokeless tobacco product) also had higher risks: 

• SIDD: 19 per cent higher 
• SIRD: 13 per cent higher 

While snus isn’t common in India, products like gutkha, khaini, and zarda are widely used — and may pose similar dangers.

Do genetics make smokers even more vulnerable?

Yes. The study also looked at people with a genetic predisposition to diabetes. Heavy smokers with high genetic risk for impaired insulin secretion were 3.5 times more likely to develop SIRD compared to those without these risk factors.

 

This suggests smoking and genetics may combine to amplify diabetes risk, a major concern for Indians, who already have strong genetic susceptibility to diabetes.

Why is this study important for India?

India has over 100 million people living with diabetes, according to the International Diabetes Federation (IDF). Many develop the condition earlier in life, and tobacco use — smoking and smokeless — is widespread. This makes the findings especially alarming for the Indian population.

What can you do right now to cut your risk?

• Quit smoking and seek support through nicotine replacement therapy, counselling, or support groups 
• Avoid smokeless tobacco — it’s not a safer alternative 
• Adopt a healthy lifestyle with regular exercise, fibre-rich foods, and weight management 
• Get screened early, especially if you smoke or have a family history of diabetes

 

As study author Emmy Keysendal from Karolinska Institutet put it:

 

“Our findings emphasise the importance of smoking cessation in the prevention of type 2 diabetes. Genetic information may help identify individuals most likely to benefit from extra support in stopping smoking.”

 

For India — where diabetes is already an epidemic — this research is yet another urgent reminder: putting out that last cigarette may protect you from far more than you think. 

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This content is for informational purposes only and is not a substitute for professional medical advice.