Sweden: Prenatal exposure to smoking is notably associated with a reduced type 1 diabetes (T1D) risk during childhood, but not after the child turns 25, according to a nationwide Swedish study involving more than 3 million people.
Young adults who smoked were not at a lower risk for T1D development, and the evidence showed that in this group, the risk for adult-onset type 1 diabetes may have increased. The research is a preprint study by investigators at Karolinska Institute in Stockholm on Preprints with The Lancet and has not yet been peer-reviewed.

Previous studies have linked prenatal smoking exposure to a lower type 1 diabetes risk in children versus those with nonsmoking mothers. Still, none of them have addressed whether this protection continues into adulthood or applies to smoking adults. The study by Sofia Carlsson, Karolinska Institutet - Institute of Environmental Medicine, and colleagues is the first to investigate maternal smoking during pregnancy concerning T1D incidence in offspring beyond childhood.
The researchers employed cohort and sibling design. They determined if the risk of adult-onset T1D is lowered in individuals exposed to smoking prenatally or during adulthood. They linked Swedish nationwide registers and prospectively analyzed T1D incidence (n=18 789) concerning maternal smoking during pregnancy (n=3 176 072) and adult smoking (n=1 608 291). The participants were followed until age 30 or year 2019.
The study led to the following findings:
Maternal smoking during pregnancy was significantly linked with a lower risk of type 1 diabetes in children aged 0 to 18 than children born to nonsmoking mothers (hazard ratio (HR), 0.76).
The HR for incident type 1 diabetes was also significant, 0.88 for offspring 19 to 30 years old.
The analysis revealed no dose-response relationship between the amount of maternal smoking and the offspring's diabetes incidence. The observed associations were not affected by adjusting smoking and body weight index by the offspring.
The data revealed a 22% to 29% lower type 1 diabetes incidence in the offspring of smoking versus nonsmoking mothers until they attained the age of 24 years. Still, no difference existed among 25 to 30 years old offspring.
Personal smoking history was significantly linked with incident T1D in people with a family history of diabetes, with a significant hazard ratio of 1.34. Still, no significant association existed for those without this family history.
"The findings indicate that a potential beneficial effect of tobacco exposure is limited to the prenatal period and T1D developing during childhood," the authors wrote. "Adult smoking may be a risk factor for adult-onset T1D, especially in people with a family history of diabetes."
The authors cautioned that their findings' clinical significance was "difficult to see", considering smoking's adverse effects during pregnancy. They instead highlighted that their findings add to understanding the aetiology of type 1 diabetes.
Reference:
Carlsson, Sofia and Wei, Yuxia and Andersson, Tomas and Feychting, Maria and Edstorp, Jessica, Prenatal and Adult Exposure to Smoking and Incidence of Type 1 Diabetes in Children and Adults – A Nationwide Study with a Family-Based Design. Available at SSRN: https://ssrn.com/abstract=4402724 or http://dx.doi.org/10.2139/ssrn.4402724