Living in a tree-lined street may cut the risk of children suffering from asthma.
That's the opinion of scientists from Columbia University, who found that asthma rates among children aged four and five fell by 25% for every extra 343 trees per square kilometre.
They believe that having nearby greenery encourages children to be more active outdoors. The trees may also improve air quality, although they say the true reason for their observation is unclear.
The study appears in the Journal of Epidemiology and Community Health.
US rates of childhood asthma soared between 1980 and 2000, with particularly high rates in poor, urban communities.
In New York City childhood asthma is the number one cause of hospital admissions for children under the age of 15. The researchers found the city had an average of 613 street trees per square kilometre, and 9% of young children had asthma.
Some experts believe that children who are exposed to microbes early in their lives are less susceptible to asthma because they have strengthened their immune systems.
The implication is that if trees make children play outside then they are exposed to more microbes, which may protect them from asthma in later life.
Conversely, trees are a source of pollen which is known to aggravate the symptoms of asthma.
Lead researcher Dr Gina Lovasi admitted the effect, if any, of trees was far from clear.
She said: "There may be something else healthful about the areas that had more trees.
"For example, trees could be more abundant in areas that are well maintained in other ways."
New York City aims to plant 1 million extra trees by the year 2017.
That's the opinion of scientists from Columbia University, who found that asthma rates among children aged four and five fell by 25% for every extra 343 trees per square kilometre.
They believe that having nearby greenery encourages children to be more active outdoors. The trees may also improve air quality, although they say the true reason for their observation is unclear.
The study appears in the Journal of Epidemiology and Community Health.
US rates of childhood asthma soared between 1980 and 2000, with particularly high rates in poor, urban communities.
In New York City childhood asthma is the number one cause of hospital admissions for children under the age of 15. The researchers found the city had an average of 613 street trees per square kilometre, and 9% of young children had asthma.
Some experts believe that children who are exposed to microbes early in their lives are less susceptible to asthma because they have strengthened their immune systems.
The implication is that if trees make children play outside then they are exposed to more microbes, which may protect them from asthma in later life.
Conversely, trees are a source of pollen which is known to aggravate the symptoms of asthma.
Lead researcher Dr Gina Lovasi admitted the effect, if any, of trees was far from clear.
She said: "There may be something else healthful about the areas that had more trees.
"For example, trees could be more abundant in areas that are well maintained in other ways."
New York City aims to plant 1 million extra trees by the year 2017.
