Population mixing and childhood diabetes

Background Exposure to infections, particularly in early life, may modify t he risk of developing childhood diabetes. Population mixing, based on the n umber and diversity of incoming migrants to an area can be used as a proxy measure for exposure to infections. We tested the hypothesis that incidence of childhood Type 1 diabetes is higher in areas of low population mixing. Methods Children (< 15 years) diagnosed with diabetes between 1986-1994 in Yorkshire, UK (n = 994) were analysed with demographic data and denominator populations from the 1991 UK Census. Population mixing was estimated separ ately for 'any age' (>1 year) and children (1-15 years) for each area, usin g the proportion of migrants and an index of diversity based on numbers and origins of migrants. Regression models calculated the effect of 'any age' and childhood population mixing on the incidence of diabetes, controlling f or population density, ethnicity and proportion of migrants. Results Areas with low levels of population mixing of children (bottom deci le), were significantly associated with higher incidence of childhood diabe tes for 0-14 years (incidence rate ratio [IRR] = 1.46, 95% CI:1.01-2.11). W hen stratified by age different effects were observed for childhood populat ion mixing with raised IRR for ages 5-9 (2.23, 95% CI:1.20-4.11) and 10-14 (1.47, 95% CI:0.89-2.42), and decreased IRR for 0-4-year-olds (0.56, 95% CI :0.17-1.82). Conclusion The incidence of childhood diabetes is highest in areas where li mited childhood population mixing occurs and the diversity of origins of in coming children is low; those over 4 years are at greatest risk. This is co nsistent with an infectious hypothesis where absence of stimulation to the developing immune system increases vulnerability to late infectious exposur e, which may precipitate diabetes.