FRIDAY, Aug. 15 (HealthDay News) -- Boys may be more likely to have childhood asthma than girls, but they are also more likely to grow out of it, a new study says.

The report, published in the second August issue of the American Journal of Respiratory and Critical Care Medicine, found that boys also have fewer asthma occurrences in the post-pubertal years.

The study tracked more than 1,000 children, ages 5 to 12, with mild to moderate persistent asthma over nine years. Each child received an annual spirometric testing with methacholine challenges to quantify their airway responsiveness (AR).

After an average of 8.6 years, boys became increasingly tolerant over time to larger and larger doses of methacholine, which provokes airway constriction, suggesting a possible decrease in disease severity. By age 16, it took more than twice as much methacholine to provoke a 20 percent constriction in the boys' airway on average as it did with the girls'.

Over the years, the girls' reactivity did not change markedly. By age 18, only 14 percent of the girls showed no significant degree of airways responsiveness, compared to 27 percent of boys.

"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," the lead researcher, Dr. Kelan G. Tantisira of Brigham and Women's Hospital and Harvard Medical School, said in a news release issued by the journal's publisher.

More information

The National Institutes of Health has more about asthma.