Early pollen exposure ups wheeze risk

Young babies who are exposed to high levels of pollen and fungal spores are at an increased risk of being wheezy, the results of a new study indicate.

Wheezing can be described as a high pitched whistling sound during breathing. It occurs when air flows through narrowed breathing tubes. Wheezing is a sign that a person may be having breathing problems. It can be caused by a number of things, including asthma, bronchitis and smoking.

US researchers assessed the seasonal impact of high levels of outside airborne fungal spores and pollen on the risk of developing wheeze in 514 children.

The respiratory health of all the children was tracked from birth until they were two years of age. Signs of early wheezing were confirmed by medical records and blood samples which measured levels of specific types of T cells (Th1 and Th2). T cells are involved in the inflammatory processes that cause the airways to narrow in response to particular triggers, resulting in wheezing or an asthma attack.

Almost 7% of the children were diagnosed with wheeze by the age of two. Factors such as environmental tobacco smoke, poverty and lower respiratory tract infections during the first year of life all increased the risk of early wheezing.

However the researchers also found a clear pattern in relation to the month the children were born in.

Those born between mid-February and March 2000, and between late August 2000 and early January 2001, were three times more likely to wheeze before the age of two than children born outside those months. These months coincided with the periods of highest circulating levels of outdoor fungal spores.

While the association with early wheeze and overall spore levels was weak, exposure to two particular types - basidospores and ascospores - during the first three months of a child’s life was associated with a significantly increased risk of wheeze. Basidospores and ascospores are released during rainfall or when humidity increases.

Furthermore children exposed to high levels of pollen from cypress, pine, and alder during their first three months of life were also significantly more likely to wheeze. These children had lower Th1 levels and higher Th2 levels by the age of two, a pattern that is consistent with asthma symptoms.

These findings were independent of other potential seasonal risk factors, such as dampness and the presence of rodents in the home.

“It is thought that the priming of a child’s T cells to respond to allergens occurs during the late stages of pregnancy, and that early exposure to allergens after birth may reinforce an abnormal T cell response,” said the team from the University of California at Berkeley.

Details of these findings are published in the journal, Thorax.

For more information on asthma, see...http://www.irishhealth.com/clin/asthma/index.html

[Posted: Tue 24/02/2009]