Smoking Linked to Increased Risk of All Subtypes of Type 2 Diabetes

Smoking of any duration substantially increases the risk of developing all 4 subtypes of type 2 diabetes (T2D) compared with not ever having smoked, according to data presented at the European Association for the Study of Diabetes (EASD) annual meeting in Vienna, Austria, September 15-19. Researchers from Sweden, Norway, and Finland reported that the strongest association was observed for individuals with severe insulin-resistant diabetes (SIRD).

Emmy Keysendal, PhD candidate at Karolinska Institute

Courtesy of Karolinska Institute

Researchers, led by Emmy Keysendal, a PhD student at Karolinska Institutet, in Stockholm, analyzed data for 3,325 individuals with T2D: 495 with severe insulin-deficient diabetes (SIDD), 477 with SIRD, 693 with mild obesity-related diabetes (MOD), and 1,660 with mild age-related diabetes (MARD), and 3,897 controls sourced from the Norwegian HUNT study, which included an average follow-up of 17 years, and the Swedish ESTRID case-control study.

Ever smokers, defined as those currently smoking or having smoked in the past, were more than 2 times as likely as never smokers to develop SIRD (relative risk [RR], 2.15; 95% CI, 1.64-2.82). Risks also increased for the other subtypes:

• 20% for SIDD (RR, 1.20; 95% CI, 0.98-1.47)
• 29% for MOD (RR, 1.29; 95% CI, 1.06-1.57)
• 27% for MARD (RR, 1.27; 95% CI, 1.12-1.44)

Smoking accounted for more than one-third of SIRD cases, compared with fewer than 15% of cases of the other 3 subtypes.

“It is clear that smoking increases the risk of type 2 diabetes whatever the subtype, that is, regardless of whether the diabetes is characterised by insulin resistance, lack of insulin, obesity or old age,” Keysendal said in a statement. “The strongest association was seen for the subtype characterised by severe insulin resistance, which suggests that smoking may contribute to diabetes by impairing the body’s ability to respond to insulin," she added.

Heavy Smoking Doubles Risk

Keysendal and colleagues reported that heavy smoking—defined as at least 20 cigarettes a day for 15 years or equivalent—further increased the risk. Compared with people who had never smoked, these individuals were 2.35 times more likely to develop SIRD (95% CI, 1.72-3.23), 52% more likely to develop SIDD (RR, 1.52; 95% CI, 1.19-1.95), 57% more likely to develop MOD (RR, 1.57; 95% CI, 1.22-2.02), and 45% more likely to develop MARD (RR, 1.45; 95% CI, 1.22-1.69), according to the results.

When researchers assessed the association between the use of snus, a smokeless tobacco product popular in Scandinavia, and the 4 T2D subtypes, the data linked heavy use to higher risks of SIDD (19%) and SIRD (13%) compared to never users.

Genetics Amplify Risk

The team found further that risks for T2D were amplified by genetic susceptibility. Specifically, individuals with a high genetic risk for impaired insulin secretion who also smoked heavily had more than a threefold increased risk (3.52-fold) of developing SIRD compared to those without these risk factors. A Mendelian randomization analysis confirmed the association between smoking and T2D subtypes, with odds ratios of 1.49 for SIDD, 1.55 for SIRD, 1.52 for MOD, and 1.26 for MARD.

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.”