London (PTI): Boys suffering from asthma are more likely than girls to wheeze in childhood but they're also more likely to shed these symptoms when they hit their teenage years, a new study has revealed.

Researchers at Harvard Medical School have based their findings on an analysis of lung functions of 1,000 kids over a period of nine years -- all were aged between five and 12, and had mild to moderate asthma when they enrolled in the study.

According to lead researcher Dr Kelan Tantisira, it's the first time that the gender differences in asthma have been documented in this way. He suggested that sex hormones might play a role in the symptoms of the condition and its severity.

In fact, in their annual tests over nine years, the researchers gave the subjects a drug to cause narrowing of the airway, and noted the dosage that was needed to do this.

While the amount of the drug needed in girls did not change much over time, in many of the boys, bigger and bigger doses were needed year on year, suggesting that the severity of their asthma was decreasing.

By the age of 18, only 14 per cent of the girls did not react to the drug, compared with 27 per cent of boys, the 'BBC News' portal reported.

"While our results were not unexpected, they do point to intriguing potential mechanisms to explain the gender differences in asthma incidence and severity. Especially intriguing is that the differences in gender begin at the time of transition into early puberty," Dr Tantisira said.

The study has been published in the 'American Journal of Respiratory and Critical Care Medicine'.