To investigate associations between country of birth, parental country of birth, and education with respect to incidence rate and time trends of type 1 diabetes mellitus (T1DM) among children and young adults.Methods
We followed a nation-wide cohort of 4469671 males and 4231680 females aged 0–30 yr between 1969 and 2008. Incidence rate ratios (IRRs) with 95% confidence intervals (CIs) for T1DM were calculated using Poisson regression models. We further calculated age-standardized rates (ASRs) of T1DM, using the world population as standard.Results
During the study period, the ASR of T1DM increased among children younger than 15 yr, but not among young adults (15–30 yr). Compared with Swedish-born children, male and female immigrant children had 44 and 42% lower IRR of TIDM, respectively. Among offspring to immigrants, corresponding decreases in IRRs were 27 and 24%, respectively. Compared with children to parents with high education, male children to parents with low education had a 10% decreased IRR of T1DM, while no effect was observed among females. The IRR of T1DM increased with increasing age and calendar time of follow-up in both sexes (p-for trend <0.0001). In young adults, the IRR among immigrants decreased by 32% in males and 22% in females, while corresponding reductions in IRRs were less in offspring to immigrants.Conclusions
We found a lower IRR of T1DM among offspring to immigrants, but especially among young immigrants compared with Sweden-born individuals. The findings show that environmental factors are important in the etiology of T1DM.