Planting trees could help fight against asthma
TREE-LINED STREETS may be carrying out a silent defence against deadly asthma attacks, according to a new study.
Researchers from the University of Exeter’s media school studied the impact of urban greenery on the potentially life-threatening respiratory condition and say their findings suggest planting trees could help reduce the effects of traffic pollution on Britons’ respiratory health.
Asthma affects about five million people in the country – including a quarter of 13 to 14-yearolds, at an annual cost of £1bn to the NHS.
The condition is also said to cause about 1,000 deaths per year across the country. The study, published in the
journal, explored more than 650,000 serious asthma attacks over a 15year period in England.
By comparing 26,000 urban neighbourhoods, the researchers found a link between areas highly populated by trees and lower rates of emergency visits to hospital for asthma.
The association was even stronger in highly polluted areas.
In the most polluted urban areas, a high density of trees was more strongly linked with low rates of people being taken to A&E than relatively unpolluted neighbourhoods.
Study leader Dr Ian Alcock said trees proved both a defence mechanism and an irritant for asthma sufferers.
He explained that while trees can remove the air pollutants that trigger asthma attacks, they can also spread allergenic pollen. Foliage can retain build-ups of the irritating pollutants that would otherwise have been dispersed by wind.
Yet the study showed an extra 300 trees per square kilometre were associated with about 50 fewer emergency asthma cases per 100,000 residents over a 15year period.
The researchers found that, on balance, trees did “significantly more good than harm”, but the benefits were not equal everywhere, Dr Alcock said.
“Green space and gardens were associated with reductions in asthma hospitalisation at lower pollutant levels, but not in the most polluted urban areas. With trees it was the other way round.
“It may be that grass pollens become more allergenic when combined with air pollutants so that the benefits of greenspace diminish as pollution increases. In contrast, trees can effectively remove pollutants from the air, and this may explain why they appear to be most beneficial where concentrations are high.”
The study also noted that asthma was strongly linked to socioeconomic deprivation, with the researchers controlling for that factor.