Study finds link between birth order and asthma symptoms

May 7, 2008 – Among four year-olds attending Head Start programs in New York City, those who had older siblings were more likely to experience respiratory symptoms including an episode of wheezing in the past year than those who were oldest or only children. Children with at least two older siblings were also 50% more likely than other children to have gone to an emergency department or been hospitalized overnight for breathing problems. These findings from the Columbia University Mailman School of Public Health were recently pre-published online in the journal Clinical and Experimental Allergy.

“Our findings support the hypothesis that having older siblings increases a child’s risk of exposure to infectious agents before age two years, and in turn increases the child’s risk for wheezing,” said Matthew Perzanowski, PhD, assistant professor of Environmental Health Sciences at the Mailman School of Public Health and the lead author of the paper. “Some studies have found that having older siblings increases the risk of wheeze in babies and toddlers. Our findings are novel in that we found that among the four year-olds in this study, the pattern was the same as has been observed in younger children elsewhere.”

The children in the study were selected for participation because they attended Head Start programs in neighborhoods with the highest rates of childhood asthma hospitalization in New York City.

One possible explanation for the association is that children with older siblings have more exposure to respiratory infections at an early age than oldest or only children. Respiratory infections are a common cause of wheezing in very young children. This study shows that children with older siblings may be appropriate targets for interventions to reduce the risk of infections that may lead to hospitalization.