Fetal exposure to parental smoking and the risk of type 2 diabetes in adult women.

OBJECTIVE We evaluated the associations of both maternal and paternal smoking during pregnancy with the risk of type 2 diabetes in daughters and explored whether any association was explained by weight at birth or BMI throughout life. RESEARCH DESIGN AND METHODS We used data from 34,453 participants of the Nurses' Health Study II. We used Cox proportional hazards models to examine the associations of maternal and paternal smoking during pregnancy with incidence of type 2 diabetes in daughters between 1989 and 2009. RESULTS Maternal smoking during the first trimester only was associated with the risk of type 2 diabetes in the offspring, independent of confounders, birth weight, and later-life BMI (fully adjusted hazard ratio 1.34 [95% CI 1.01, 1.76]). In the age-adjusted models, both continued maternal smoking during pregnancy and paternal smoking tended to be associated with an increased risk of type 2 diabetes in daughters. Perinatal and adult life variables did not explain these associations, but additional adjustment for current BMI fully attenuated the effect estimates. CONCLUSIONS The associations of maternal and paternal smoking during pregnancy with the risk of type 2 diabetes in daughters were largely explained by BMI throughout the life course. Further studies are needed to explore the role of first-trimester-only maternal smoking on insulin resistance in the offspring. Also, similar effect estimates for maternal and paternal smoking suggest that the associations reflect shared family-based or lifestyle-related factors.