Tree-lined streets 'reduce asthma'
01 May 2008

Children who live in tree-lined streets have lower rates of asthma, a New York-based study suggests.

Columbia University researchers found that asthma rates among children aged four and five fell by 25% for every extra 343 trees per square kilometre.

They believe more trees may aid air quality or simply encourage children to play outside, although they say the true reason for the finding is unclear.

The researchers found the city had an average of 613 street trees per square kilometre, and 9% of young children had asthma.

The link between numbers of trees and asthma cases held true even after taking into account sources of pollution, levels of affluence and population density, the researchers said.

This report is the first to link trees with asthma but it doesn’t investigate the reasons why street trees may have a positive impact of levels of asthma in their local street.

A number of other studies have confirmed that environmental factors such as traffic fumes, pollen, and cold air can make people with asthma’s symptoms worse, although so far it is not known whether they actually cause asthma.

Leanne Male, Assistant Director of Research at Asthma UK said: ‘Previous research looking at the influence of the environment on levels of asthma has focused on negative aspects, such as pollution and chemical exposure.

'This innovative report is the first to look specifically at the potentially beneficial effects of trees in urban areas and raises some interesting issues. However, there are a number of other factors that have not been considered, for example whether the families involved have pets. Despite the need for further work, this is a positive first step into a new area of research linking the environment and asthma.’