In Jamaica, there is a superstitious belief that if an asthmatic stands beside a tree and the tree is then chopped at the persons height, the asthma will be stopped dead in its tracks and not bother the sufferer anymore.

They might have been on the right track as researchers have pointed to the effect trees have on the prevalence of asthma.  

Living on a tree-lined street reduces a child's risk of developing asthma compared with life in a grey inner-city neighbourhood, say researchers.

The researchers measured the number of trees in New York and compared the results with the number of children diagnosed with asthma.

What they found was a lower rate of the disease among children aged four and five who lived in areas of the city with more trees.  Asthma rates fell by 25% when there were approximately 350 more trees in a square kilometre.

Dr. Gina Lovasi from Columbia University said, "Street trees may explain geographic variation in the prevalence of asthma within urban environments" and "may help prevent asthma, either by encouraging outdoor play or through an effect on local air quality."

It has been argued by some scientists that children exposed to allergens like pollen in their early years trains the immune system to be less sensitive to allergens.

Meanwhile, Professor Irwin McLean, who studies asthma at the University of Dundee, said it was a "very interesting study" but he urged caution in interpreting the results. "It shows that there is some correlation between suburban living and a reduction in asthma. That doesn't mean you should go out and plant a load of trees around your house if you want to stop your kids from getting asthma," he said.

 "It is very difficult in environmental studies to dissect out one single triggering factor. There won't be a motorway running through a tree-lined suburb, for example, with all the pollution associated with that. The obvious thing people are going to think is, if I plant a load of trees around me that will protect me from asthma.  If you were living by the side of a motorway and you planted a forest around you, you are still going to get asthma - if the motorway is the cause of the asthma," McLean further stated.