The risk for type 1 diabetes mellitus (T1DM) is increased in the second compared with the first generation of immigrants in Sweden. We investigated the effect of the mother's duration of stay in Sweden on the risk of T1DM in the offspring.
Using data from national registries, we identified all subjects with T1DM among 984,798 children born in Sweden (aged 0-18 years) between 1992 and 2009. Incidence rate ratios (IRRs) with 95% CI were estimated using Poisson regression.
Offspring of mothers living in Sweden for up to 5 years had a 22% lower risk of T1DM (adjusted IRR 0.78, 95% CI 0.63-0.96) compared with offspring of mothers living in Sweden for 11 years or more. The risk increased with the mother's duration of stay in Sweden.
Our findings support the hypothesis that immigration to Sweden is associated with exposure to new environmental factors that contribute to the development of T1DM in genetically susceptible individuals.