Boys are more likely to grow out of childhood asthma during puberty than girls, according to the results of a US study.
It showed that the airway responsiveness of boys diagnosed with mild to moderate asthma started to drop after age 11, but remained level in girls.
The study included 1,041 children aged five-12 years with mild to moderate persistent asthma who were followed up for an average of nine years.
They underwent yearly methacholine challenges to test for changes in airway responsiveness.
Airway responsiveness improved at the same rate in boys and girls until age 11.
After this it improved in boys but not in girls. At age 16, the average methacholine dose needed to provoke a 20 per cent loss of FEV1 in boys was more than double the dose needed to provoke the same response in girls.
At age 18, 27 per cent of the boys no longer responded to the methacholine challenge, indicating that they had grown out of their childhood asthma. This was true in only 14 per cent of the girls.
Lead research Dr Kelan Tantisira, from the pulmonary division of Brigham and Women's Hospital and Harvard Medical School in Boston, said that the timing of the changes between boys and girls in airway responsiveness found in this study indicates that sex hormones released at puberty are likely to be a factor.
Increased testosterone levels may reduce airways responsiveness, while estrogen could increase it, he added.
'We now know that airway responsiveness drops off a lot more in boys than girls during the teenage years, so where you might be happy stopping controller medication for boys who say that their symptoms are better, for many girls it might be worth taking a more cautious approach,' he said.
He added that in the future there could be different asthma medications for girls and boys.
Am J Respir Crit Care Med 2008; 178: 325-31