A new study suggests that growing up on a tree-lined street is good for a child's health, as asthma rates are lower in kids who grow up in leafy green neighbourhoods.

Asthma rates among four- and five-year-olds in New York City fell by almost a quarter for every increase in tree density that measured 343 more trees per square kilometre.

For their study, researchers from Columbia University looked at asthma rates among 4 and 5 year olds, as well as asthma-related hospital admissions for kids up to age 15, in New York City. Researchers analyzed information from 42 health-service districts.

They then compared the information to city data from those same districts that outlined the number of trees, sources of pollution, population density and the ethnic makeup of the area.

However, the study concluded that rates of asthma-related hospital admissions among older children were not affected by tree density when researchers included other factors such as the children's proximity to sources of pollution, and their neighbourhood's population density and level of affluence.

The study was published in the Journal of Epidemiology and Community Health.

In their study, the researchers said that trees may help decrease asthma rates because kids may be more inclined to play outside when there are a lot of trees in their neighbourhoods. Trees improve air quality by absorbing carbon dioxide and release oxygen.

"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," the authors wrote.

"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 researchers said that in the United States, asthma rates in children have grown 50 per cent between 1980 and 2000, particularly in poorer, urban communities.

In New York City, asthma is the main cause of hospital admission among kids under age 15.

In Canada, asthma affects about three million people, according to The Asthma Society of Canada.

It is a chronic condition that causes inflammation of the airways, which can lead to shortness of breath, tightness in the chest, coughing and wheezing. There is no cure, but there are medications that can lessen the severity of symptoms, and sufferers can avoid symptom triggers that can range from exposure to pollen and mould to smoking and engaging in vigorous exercise.

Abstract:

Children living in areas with more street trees have lower prevalence of asthma

G S Lovasi, J W Quinn, K M Neckerman, M S Perzanowski, A Rundle

Background: The prevalence of childhood asthma in the USA increased by 50% from 1980 to 2000, with especially high prevalence in poor urban communities.

Methods: Data on the prevalence of asthma among children aged 4-5 years and on hospitalisations for asthma among children less than 15 years old were available for 42 health service catchment areas within New York City. Street tree counts were provided by the New York City Department of Parks and Recreation. The proximity to pollution sources, sociodemographic characteristics and population density for each area were also measured.

Results: Controlling for potential confounders, an increase in tree density of 1 standard deviation (SD, 343 trees/km2) was associated with a lower prevalence of asthma (RR, 0.71 per SD of tree density; 95% CI, 0.64 to 0.79), but not with hospitalisations for asthma (RR, 0.89 per SD of tree density; 95% CI, 0.75 to 1.06).

Conclusions: Street trees were associated with a lower prevalence of early childhood asthma. Our study does not permit inference that trees are causally related to asthma at the individual level. The PlaNYC sustainability initiative, which includes a commitment to plant one million trees by the year 2017, offers an opportunity for a large prospective evaluation.

Link to Full Study (Requires registration)