Being born in Sweden increases the risk for type 1 diabetes - a study of migration of children to Sweden as a natural experiment

Aim: To investigate whether the age of first exposure to a high-incidence country like Sweden determines the risk of T1DM in children with an origin in a low incidence region of the world. Methods: Register study in a Swedish study population in the age 6-25 years in three categories of residents with an origin in low incidence regions of T1DM (Eastern Europe, East Asia, South Asia and Latin America); 24 252 international adoptees; 47 986 immigrants and 40 971 Swedish-born with two foreign-born parents and a comparison group of 1 770 092 children with Swedish-born parents. Retrieval of a prescription of insulin during 2006 was used as an indicator of T1DM and analysed with logistic regression. Results: The odds ratios (OR) for T1DM were lower than the Swedish majority population for residents with an origin in the four low incidence regions. Being Swedishborn implied a higher risk for T1DM in the four low incidence study groups compared with the internationally adopted with an OR of 1.68 (CI 1.03-2.73). Conclusions: Being born in Sweden increases the risk for T1DM in children with an origin in low incidence countries. This may imply that exposures in utero or very early infancy are important risk factors for T1DM.