How, when and where a child is born may all play a role in lifetime asthma risk, new studies suggest.
Asthma occurs when airways in the lungs spasm and swell, restricting the supply of oxygen. The incidence of asthma in the United States has risen steadily for more than two decades, and about 6 percent of children now have asthma, up from less than 4 percent in 1980, according to the Centers for Disease Control and Prevention.
The reasons for the increase are not entirely clear. Genetics probably plays a role in the risk for asthma, but an array of environmental factors — pollen, dust, animal dander, mold, cockroach feces, cigarettes, air pollution, viruses and cold air — have all been implicated in its development.
This month, The American Journal of Respiratory and Critical Care Medicine is reporting that children born in the fall have a 30 percent higher risk for asthma than those born in other seasons. The finding is based on a review of birth and medical records of over 95,000 children in Tennessee.
A possible explanation is that autumn babies tend to be about 4 months old at the peak of cold and flu season. By that age, many babies are in day care and regularly exposed to the outside world.
http://www.nytimes.com/2008/12/09/health/research/09asthma.html?em