Background: Previous literature has indicated that environmental exposures in childhood influence development of atopic sensitization.
Objective: We sought to study the association between childhood environment and adult atopy.
Methods: Thirteen thousand nine hundred thirty-two subjects aged 20 to 44 years from 36 areas in Europe, New Zealand, the United States, and Australia took part in the European Community Respiratory Health Survey, answering interviewer-led questionnaires and providing blood tests for measurement of specific IgE to grass, house dust mite, cat, and Cladosporium allergens.
Results: Atopy was negatively associated with family size (OR = 0. 93; 95% CI = 0.90-0.96 per 1 sib), partly attributable to an independent protective effect of a greater number of brothers (OR = 0.92; 95% CI = 0.89-0.95 per 1 brother). Accounting for total number of siblings, no further influence was detected for number of older or younger siblings. Bedroom sharing was associated with a lower prevalence of atopy, particularly to cat allergen. A protective effect of family size and bedroom sharing could only be detected in subjects reporting no parental allergy (family size, test for interaction P =.012). The presence of a dog in the home in childhood was negatively associated with adult atopy (OR = 0.85, 95% CI = 0. 78-0.92), an effect that remained after adjustment for parental allergy, sibling allergy, and adult pet ownership.
Conclusion: Subjects from large families with brothers, shared bedrooms, and dogs in childhood were less often atopic as adults. Our findings are consistent with the hypothesis that infectious agents could inhibit development of atopy during childhood. However, in subjects with a strong genetic predisposition, environmental factors in childhood are possibly of less importance.