Matthew Perzanowski of the Columbia University Mailman School of Public Health looked at 4-year-old children in Head Start programs in neighborhoods with the highest rates of childhood asthma hospitalization in New York.

The study, published online in Clinical and Experimental Allergy, found those with older siblings more likely than other children to experience respiratory symptoms -- including an episode of wheezing -- in the past year.

Children with two or more older siblings were 50 percent more likely to have gone to the hospital for breathing problems.

"Our findings support the hypothesis that having older siblings increases a child's risk of exposure to infectious agents before age 2, and in turn increases the child's risk for wheezing," Perzanowski said in a statement.

"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 4-year-olds in this study, the pattern was the same as has been observed in younger children elsewhere."