Background Data on the relationship between Th2-biased atopic disorders and Th1-biased autoimmune diseases such as type 1 diabetes are conflicting. Many studies have not defined the time sequence of disease appearance, and few have investigated the role of candidate risk factors.
Objective The objective was to investigate whether the presence of parents' report of physician-diagnosed atopic disorders is lower among cases of type 1 diabetes before diagnosis, as compared with population-based control subjects, and whether this may be explained by candidate risk factors such as day-care attendance, breastfeeding habits, and perinatal factors.
Methods We designed a population-based case–control study in Norway with 545 cases of childhood-onset type 1 diabetes and 1668 control subjects. Families were contacted by mail, and they completed a questionnaire on physician-diagnosed atopic eczema, allergic rhino-conjunctivitis and asthma, and other relevant factors. Data on birth order, maternal age at delivery, birth weight, gestational age, pre-eclampsia, and caesarean section were obtained from the Medical Birth Registry of Norway by record linkage.
Results Atopic eczema was inversely associated with risk of type 1 diabetes, odds ratio=0.55 (95% confidence interval 0.35–0.87) after adjustment for age, sex, maternal education, day-care attendance, duration of exclusive breastfeeding, and perinatal factors. Allergic rhino-conjunctivitis and asthma were not significantly associated with type 1 diabetes.
Conclusions Atopic eczema was associated with a lower risk of type 1 diabetes, independent of a number of candidate risk factors, suggesting that it may confer partial protection against type 1 diabetes.