Parents have many reasons to want to help keep their children active and at a healthy weight. Preventing asthma has just been added to the list. Nearly a million children in the U.S. — about a quarter of kids diagnosed with asthma in childhood — could have avoided developing this the chronic disease by staying at a healthy weight.

Obese children, those with a body mass index or BMI in the 95th percentile or above, were 30 percent more likely to develop asthma than kids who were a healthy weight.

“Asthma is the No. 1 chronic disease in children and some of the causes such as genetics and viral infections during childhood are things we can't prevent,” explained study author, Jason E. Lang, of Duke University. “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.”

The findings on the association between an asthma diagnosis and obesity are based on information from over a half million children who made more than 19 million doctor visits at six major health centers.

Obese children, those with a body mass index or BMI in the 95th percentile or higher, were 30 percent more likely to develop asthma than kids who had a healthy weight. The risk of asthma fell with children's weight: Kids who were overweight, rather than obese, with a BMI in the 85-94th percentile, had a 17 percent greater chance of being diagnosed with asthma. And the rates of asthma continued to decline with children's weight. Gender, age, socioeconomic status and allergies had no affect on children's asthma risk.

The inflammation obesity brings to the body may be what's behind the increase in asthma risk. The association seen in the findings and the fact that weight loss often improves asthma symptoms suggest obesity may be directly to blame for asthma in certain children. The study found a clear association between obesity and overweight and the likelihood of developing asthma, but more research is needed to fully understand the mechanisms that might be at work and cement a causal connection.

In the meantime, the findings are another good reason for parents to do what they can to help keep their children from becoming overweight or obese.

And there is plenty you can do to avoid this risk. Feed your family healthy meals and serve them correct portion sizes. Have healthy foods like fruit, yogurt and vegetable sticks on hand for snacking. Limit sitting time — television watching and playing on devices — and encourage your children to go outside and play, or enroll them in local sports.

The study is published in Pediatrics.