Smoking Raises Risk of All Type 2 Diabetes Subtypes, New Study Finds

Previously, the scientific community proposed classifying type 2 diabetes into four subtypes: severe insulin-resistant, severe insulin-deficient, mild obesity-related diabetes, and mild age-related diabetes. They differ in severity, prognosis, and risk of complications, but until now it was unclear whether they had different risk factors.

A new study by researchers from the Karolinska Institutet in Sweden, Norway and Finland has found that smoking is a powerful, universal risk factor for all four categories.

After analyzing data from more than 3,300 patients with diabetes and nearly 3,900 controls, the researchers found:

• Current smokers (including former smokers) had a higher risk of developing any subtype of T2DM than those who had never smoked.

• The strongest link was found with severe insulin-resistant diabetes, with smoking estimated to be responsible for more than a third (35%) of all cases of this subtype.

• Heavy smoking (a pack of cigarettes a day for 15 years or more) further increased the risks. Heavy smokers had a 2.35-fold higher risk of severe insulin-resistant diabetes, and 45-57% higher risks of other subtypes.

"It is clear that smoking increases the risk of developing type 2 diabetes regardless of the subtype, that is, regardless of whether diabetes is characterized by insulin resistance, insulin deficiency, obesity or old age," said lead study author Emmy Keisendahl, a PhD student at Karolinska Institutet.

Of particular concern to the scientists was the finding that heavy snus (smokeless tobacco) use was also associated with an increased risk of severe subtypes of diabetes.

An important finding was that people with a genetic predisposition to diabetes or low insulin secretion were particularly vulnerable to the negative effects of smoking. Heavy smokers with a high genetic risk of impaired insulin secretion were more than 3.5 times more likely to develop the severe insulin-resistant subtype.

"Our findings highlight the importance of smoking cessation in preventing type 2 diabetes. They also suggest that genetic information may help identify individuals who are most likely to benefit from additional support in quitting," the study authors concluded.

The results of the study once again confirm that quitting tobacco in any form remains a key element in the strategy to reduce the global incidence of diabetes.