Atopy, home environment and the risk of childhood-onset type 1 diabetes: a population-based case–control study

Background:  The marked increases in the incidence of type 1 diabetes in recent decades strongly suggest the role of environmental influences. These environmental influences remain largely unknown.
Objective:  To investigate atopy and home environment (such as children living at home, sharing a bedroom and house moves) as potential risk factors for type 1 diabetes.
Subjects and method:  In Northern Ireland, 175 children with type 1 diabetes and 4859 control children completed a questionnaire on atopy experience, family composition and home environment. Control children from two age groups (6–8 yr old and 13–14 yr old) were identified from randomly selected primary and secondary schools across Northern Ireland. Cases were identified from a population-based type 1 diabetes register.
Results:  There was little evidence of a difference in the proportion of participants with a history of atopy in the cases compared with controls. There was a significant reduction in the risk of diabetes in children who lived with more siblings {odds ratio (OR) = 0.58 [95% confidence interval (95% CI) 0.39–0.85] in children who lived with three or more siblings compared with one or none} and in children who moved house more often [OR = 0.59 (95% CI 0.40–0.88) in children who moved house twice or more compared with never].
Conclusion:  The reduced risk of type 1 diabetes in children living with siblings, sharing a bedroom and moving house more often could reflect the protection afforded by exposure to infections in early life and consequently may provide support for the hygiene hypothesis.