|ASTHMA AND TREES|
Lovasi GS, Quinn JW, Neckerman KM, et al. Children living in areas with more street trees have lower asthma prevalence. J Epidemiol Community Health 2008 May 1. [Epub ahead of print] PMID: 18450765
From 1980 to 2000, the prevalence of childhood asthma in the US increased by 50%, with a high concentration in poor urban neighborhoods. Asthma is commonly defined as a disease of the respiratory tract in which the airway sometimes constricts and is lined with excess mucus, making breathing difficult. It is the most common reason for which children in New York City are admitted to the hospital.
The researchers involved in this study looked at the asthma rates in 4 to 5 year olds as well as the hospital admissions information for this disease in children up to age 15 in 42 health service districts in New York City. Then, this information was correlated with city data on the number of trees growing, sources of pollution, racial and ethnic make-up, and population density of the area.
There were an average of 613 trees on streets per square kilometer in the City. In total, 9% of young children had asthma. For every increase in tree density of 343 trees per square kilometer, asthma rates in this age group fell by almost 25%. This pattern held fast, even once corrections were made for sources of pollution, levels of affluence, and population density-all of which were considered likely to influence the results.
How could the presence of trees affect asthma incidence? Through activities like climbing and environmental effects like shade, children tend to congregate around trees. Trees improve air quality by removing certain pollutants and affecting oxygen levels.
New York City plans to plant 1 million trees before 2017, and this could potentially create an opportunity to truly investigate the impact of tree density on asthma. In the meantime, it makes sense to plant more trees where you can.
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