Boys are more likely than girls to have childhood asthma, but they are also more likely to grow out of it, a study carried out by a team at Harvard Medical School and Women’s Hospital in Boston showed.

The research involved taking measurements from 1,041 asthmatic children that were tested annually over a nine-year period.

The study appears in the Aug.15 issue of the American Journal of Respiratory and Critical Care Medicine.

“This is the first study to prospectively examine the natural history of sex differences in asthma in this manner,” lead researcher Dr. Kelan G. Tantisira said.

They conducted standard “methacholine challenge” tests for twitchy airways annually over a period of nearly nine years. After an average of 8.6 years boys needed larger doses of methacholine to produce a 20% decrease in forced expiratory volume, whereas girls required a smaller dose. By age 18, only 14 percent of the girls showed no significant degree of airways responsiveness, compared to 27 percent of boys.

“Especially intriguing is that the differences in gender begin at the time of transition into early puberty,” Dr. Kelan G. Tantisira of Brigham and Women’s Hospital and Harvard Medical School, said in a news release.

This is a “fascinating finding,” Dr. Jorrit Gerritsen, of Beatrix Children’s Hospital in Groningen, the Netherlands, notes in a commentary published in the American Journal of Respiratory and Critical Care Medicine.