Previous studies have shown that whereas smoking is associated with an increased risk of type 2 diabetes, primarily attributed to negative effects of nicotine on insulin sensitivity, several studies have linked parental smoking to a reduced risk of type 1 diabetes in the offspring (Dahlquist and Källén, 1992; Magnus et al., 2018), including a recent study on maternal smoking during pregnancy based on data from three different cohorts (Magnus et al., 2018). This evidence concerns the gene INS and type 1 diabetes mellitus.