Tree Density May Have Link to Childhood Asthma

May 1, 2008

A higher density of trees along city streets may be associated with a lower prevalence of early childhood asthma, according to research published online May 1 in the Journal of Epidemiology and Community Health.

THURSDAY, May 1 (HealthDay News) -- A higher density of trees along city streets may be associated with a lower prevalence of early childhood asthma, according to research published online May 1 in the Journal of Epidemiology and Community Health.

Gina Lovasi, Ph.D., of Columbia University in New York City, and colleagues analyzed statistics on asthma prevalence in young children and asthma hospitalizations in children from the New York City Department of Health, along with data from a street tree census.

An increase of tree density by 343 trees per square kilometer would be associated with a 29 percent lower early childhood prevalence of asthma, after adjusting for factors such as sociodemographic characteristics, population density and proximity to sources of pollution, the researchers report. An association between tree density and asthma hospitalizations wasn't significant after adjustment, they note.

"Our cross-sectional and ecological study does not permit inference that trees are causally related to the prevalence of childhood asthma at the individual level. These observational data may be subject to residual confounding or confounding by unmeasured characteristics. Previous studies of tree density and childhood asthma have not been published to our knowledge, and our results need to be replicated by others. Future studies may be more robust if they are able to measure and control for characteristics of the home environment, such as the presence of allergens," the authors write.

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