Weight might be the cause for one-fourth of asthma cases in kids with obesity, a recent study suggests.

The research, which studied health data from more than 500,000 children in the United States, suggested that about 10 percent of all kids aged between 2 to 17 with asthma, might have avoided the illness by maintaining a healthy weight. The findings are published in the Journal of Pediatrics.

"Asthma is the number one chronic disease in children and some of the causes such as genetics and viral infections during childhood are things we can't prevent. Obesity may be the only risk factor for childhood asthma that could be preventable. This is another piece of evidence that keeping kids active and at a healthy weight is important," said Jason E. Lang, lead author of the study.

For the retrospective study, researchers analysed data for 507,496 children from more than 19 million doctor's visits at six major children's health centers.

Those classified as having asthma had been diagnosed at two or more doctor's appointments and had also received a prescription, such as an inhaler. Tests of their lung function also confirmed they had the disease.

Children classified as obese (those with a body-mass index (BMI) in the 95th percentile or above for their age and sex) had a 30-percent increased risk of developing asthma than peers of a healthy weight.

Asthma did not affect just those with obesity. Children who were overweight but not obese (BMI in the 85-94th percentile) also had a 17-percent increased asthma risk compared to healthy-weight peers.

The researchers calculated asthma risk using several models and adjusted for risk factors such as sex, age, socioeconomic status, and allergies. The results remained similar.