Siblings, day-care attendance, and the risk of asthma and wheezing during childhood

Background: Young children with older siblings and those who attend day car e are at increased risk for infections, which in turn may protect against t he development of allergic diseases, including asthma. However, the results of studies examining the relation between exposure to other children and t he subsequent development of asthma have been conflicting. Methods: In a study involving 1035 children followed since birth as part of the Tucson Children's Respiratory Study, we determined the incidence of as thma (defined as at least one episode of asthma diagnosed by a physician wh en the child was 6 to 13 years old) and the prevalence of frequent wheezing (more than three wheezing episodes during the preceding year) in relation to the number of siblings at home and in relation to attendance at day care during infancy. Results: The presence of one or more older siblings at home protected again st the development of asthma (adjusted relative risk for each additional ol der sibling, 0.8; 95 percent confidence interval, 0.7 to 1.0; P = 0.04), as did attendance at day care during the first six months of life (adjusted r elative risk, 0.4; 95 percent confidence interval, 0.2 to 1.0; P = 0.04). C hildren with more exposure to other children at home or at day care were mo re likely to have frequent wheezing at the age of 2 years than children wit h little or no exposure (adjusted relative risk, 1.4; 95 percent confidence interval, 1.1 to 1.8; P = 0.01) but were less likely to have frequent whee zing from the age of 6 (adjusted relative risk, 0.8; 95 percent confidence interval, 0.6 to 1.0; P = 0.03) through the age of 13 (adjusted relative ri sk, 0.3; 95 percent confidence interval, 0.2 to 0.5; P<0.001). Conclusions: Exposure of young children to older children at home or to oth er children at day care protects against the development of asthma and freq uent wheezing later in childhood. (N Engl J Med 2000;343:538-43.) (C)2000, Massachusetts Medical Society.