Smoking Boosts Risk For Type-2 Diabetes Subtypes, Especially Severe Kinds

Type-2 diabetes is already one of India's biggest health challenges. According to International Diabetes Federation (IDF) estimates, India has over 100 million people with diabetes, a number projected to rise. Many Indians develop diabetes earlier, often due to combinations of genetic risk, dietary patterns, obesity, and sedentary lifestyle. Smoking remains widespread, both in forms of cigarettes, bidis, and smokeless tobacco products, amplifying health risks beyond just cancer and heart disease. One of the newer ideas in diabetes research is that type-2 diabetes isn't a single uniform disease. Instead, patients may fall into different subtypes depending on how much insulin resistance vs insulin deficiency, obesity, age, etc., determine their disease. These subtypes differ in how severe they are, how fast complications develop, and what treatments work best.

A new study, presented at the European Association for the Study of Diabetes (EASD) in September 2025, shows that smoking increases risk across all these subtypes, not just "typical" type-2 diabetes. For India, where both tobacco use and genetic predisposition to diabetes are significant, this means that smoking might worsen the burden of all forms of T2D, not just the obesity-related ones. Knowing this helps public health planners, clinicians, and individuals understand that smoking cessation can be a key preventive tool, regardless of which subtype one may be more likely to develop.

Where And How The Research Was Done

Researchers from Karolinska Institutet (Sweden) and collaborators in Norway and Finland used long-running, population-based datasets. Two major sources: the HUNT study in Norway (with around 17 years average follow-up) and the ESTRID case-control study in Sweden.

Sample sizes included 3,325 individuals with type-2 diabetes, divided into the four subtypes:

• SIRD (Severe Insulin-Resistant Diabetes) - 477 people: Severe insulin resistance where the body's tissues respond poorly to insulin and glucose remains high despite insulin presence.
• SIDD (Severe Insulin-Deficient Diabetes) - 495 people: Severe insulin deficiency where the body's insulin production is low.
• MOD (Mild Obesity-Related Diabetes) - 693 people: Mild obesity-related diabetes, which has a typically younger onset, and obesity plays a strong role.
• MARD (Mild Age-Related Diabetes) - 1,660 people: Mild age-related diabetes, which has an onset later in life, with less severe insulin resistance or deficiency initially.

Key Findings Of The Study: Risks By Subtype And Smoking Intensity

Based on the study of 3,325 individuals with diabetes and varying smoking intensities, the researchers behind this study had the following observations:

Smoking (Ever Vs Never)

• Individuals who had ever smoked (current or past smokers) were significantly more likely to develop all four subtypes, compared to never smokers.
• The highest relative risk increase was for SIRD (severe insulin resistance), i.e. approximately 2.15-times higher.
• For other subtypes: Those with SIDD had around 20% higher risk; those with MOD had approximately 29% higher risk; and those with the subtype MARD had around 27% higher risk.

Heavy Smoking Intensifies Risk

Heavy smokers (defined as less than or equal to15 pack-years or equivalent; e.g. 20 cigarettes/day for 15 years or similar) had even higher risks:

• SIRD subtype had around 2.35 times increase over never smokers
• SIDD subtype had approximately 52% higher risk
• MOD subtype had 57% higher risk
• MARD subtype had around 45% higher risk

Genetic Susceptibility Compounds Risks

The study looked also whether people who have genetic predisposition to type-2 diabetes (or to aspects like reduced insulin secretion or insulin resistance) are more vulnerable. Indeed, heavy smokers with high genetic risk for reduced insulin secretion had a 3.52-fold risk of developing SIRD compared to people without such risk factors. 

That means smoking and genetics works synergistically, worsening risk beyond either alone.

Smokeless Tobacco In Scandinavia

Interestingly, among men in Sweden, those using snus (a smokeless tobacco product) also had elevated risk for SIDD (around 19% higher) and SIRD (around 13% higher) compared to never users. While snus is not common in India, other forms of smokeless tobacco are, so this suggests non-smoking tobacco also may contribute.

Implications And Takeaways For Indians

Given what we know about smoking, genetics, and type-2 diabetes in India, here are what this study implies, and what individuals and public health systems might do:

• Smoking cessation is crucial not just for lung health, but for preventing all kinds of diabetes. Many in India may assume that smoking mainly worsens heart disease, cancer, or respiratory disease. But this study shows: regardless of whether someone is likely to develop insulin deficiency or insulin resistance, smoking pushes them into risk.
• The more you smoke (duration / intensity), the greater the danger. Heavy smokers faced much higher increases in risk across all subtypes. For many in India, bidi or cigarette smoking over many years is common. Reducing number of cigarettes, quitting earlier, etc., will meaningfully reduce risk.
• Smokeless tobacco may also be harmful. The snus finding suggests even tobacco use without smoking could increase risk of severe diabetes subtypes. India has high prevalence of smokeless tobacco use (gutkha, khaini, etc.), so studies should examine these, and users should be aware that these products are not safe.
• People with family history or known genetic risk must be extra cautious. With high rates of familial diabetes in India, many people already have an elevated baseline risk. Smoking may magnify this, especially toward the severe subtype SIRD. If someone's parents or siblings had early onset diabetes, quitting smoking becomes even more important.

What You Can Do Now

• Quit smoking or aim to reduce immediately. Seek help with nicotine replacement, counselling, etc.
• If using smokeless tobacco, consider quitting or reducing.
• Adopt a healthy lifestyle: diet rich in fibre, whole grains; regular physical activity; maintain healthy weight. These mitigate risk even in genetically predisposed persons.
• Get screened early if you smoke or have family history. The following tests are a must: fasting glucose, HbA1c, etc., so any subtype can be caught early.
• Avoid passive smoking because it contributes too (other studies show non-smoker exposure increases risk).

This new Scandinavian study adds a crucial piece to our understanding: smoking doesn't just raise risk for some types of type-2 diabetes. It increases risk across all four subtypes, especially the most severe insulin resistance type (SIRD). For India, with high genetic susceptibility, high tobacco use (both smoked and smokeless), and rising diabetes rates, the message is clear: quitting smoking (or tobacco in any form) can help prevent a wide spectrum of diabetes, not just the mild or obesity-related kinds. Interventions should target all smokers, especially those with family history or early signs of diabetes, and public policy must support tobacco control as a central tool in curbing the diabetes epidemic.

Disclaimer: This content including advice provides generic information only. It is in no way a substitute for a qualified medical opinion. Always consult a specialist or your own doctor for more information. NDTV does not claim responsibility for this information.

References:

Keysendal E, Ahlqvist E, Asvold B, et al. Tobacco Use, Genetic Susceptibility, and the Risk of Type 2 Diabetes Subtypes. Abstract presented at European Association for the Study of Diabetes, Vienna, September 15-19, 2025.

International Diabetes Federation (IDF) - Factsheets