Type I diabetes among children and young adults: the role of country of birth, socioeconomic position and sex

OBJECTIVE: 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 4 469 671 males and 4 231 680 females aged 0-30 years 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 years, but not among young adults (15-30 years). 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.