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J Pediatr. 2009 Dec;155(6):781-787.e1. doi: 10.1016/j.jpeds.2009.06.035. Epub 2009 Aug 15.

Risk of childhood asthma in relation to the timing of early child care exposures.

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  • 1Department of Public Health Sciences, University of Virginia School of Medicine, Charlottesville, VA 22908-0717, USA.



To examine whether early child care exposure influences the risk for development of asthma.


Longitudinal data from 939 children and their families from the National Institute of Child Health and Development Study of Early Child Care and Youth Development were analyzed. Exposure to other children in the primary child care setting as an infant (before 15 months) and as a toddler (16-36 months) were assessed as risk factors for persistent or late-onset asthma by age 15 via logistic regression.


The number of children in the child-care environment when the child was a toddler was significantly associated with odds of asthma, even after adjusting for respiratory illnesses and other risk factors (P < .05). The fewer the children exposed to as toddlers, the higher the probability of persistent or late-onset asthma by age 15.


This study supports the theory of a protective effect of exposure to other children at an early age, especially as a toddler, on the risk of asthma. This effect appears to be independent of the number of reported respiratory tract illnesses, suggesting that other protective mechanisms related to the number of children in the child care environment may be involved.

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