Overweight and obese children are more likely to be diagnosed with asthma, according to a new study - and when they do have the condition, it tends to be more severe than in normal weight youth.
Researchers found that heavier kids and teenagers with asthma had more emergency room visits for the condition and used more "rescue" medications.
"If parents are noticing that their overweight or obese child is having asthma-like symptoms, one thing to pay attention to, instead of just addressing the asthma, is to potentially address the child's weight," said Mary Helen Black, the study's lead author from Kaiser Permanente Southern California's department of research and evaluation.
For their study, she and her colleagues analyzed the electronic health records of 623,000 six- to 19-year-olds covered by Kaiser's health plan in 2007 through 2011. None of those children initially had asthma.
Over an average of three years, just under 32,000 of them - about five percent - were diagnosed with the condition.
The researchers found that the more children weighed, the more likely they were to develop asthma. Compared to normal weight kids, those who were overweight but not obese were 16 percent more likely to be diagnosed with asthma, and the most obese were 37 percent more likely.
That was after taking into account children's age, gender and race, the study team wrote this week in the American Journal of Epidemiology.
Among those who developed asthma, heavier kids and teens in the study also tended to have more complications than their slimmer peers.
In the year after their diagnosis, for example, 106 out of every 1,000 extremely obese youth went to the ER for asthma, compared to 87 of every 1,000 normal weight kids with asthma. And obese children were more likely to have an asthma "exacerbation" (that is, worsening of their condition) and to need "rescue" medicines, called short-acting beta agonists, when their usual medicines weren't enough.
According to the Centers for Disease Control and Prevention, one in 11 U.S. children has asthma. In 2008, asthma caused 10.5 million missed school days.
Black said it's possible the body-wide inflammation seen in obesity may affect asthma risk and severity. Or, she added, the link between obesity and asthma could be due to the direct effect of extra weight on the airways.
"Especially those (children) who are extremely obese definitely have a more restricted capacity for air exchange and things like that," Black said.
"It's a little more difficult for them mechanically to breathe."
If that's the case, Black said, "If an extremely obese child is able to get down into even the overweight range, they may have a much greater capacity for breathing normally."
Dr. Peter Michelson, a pediatrician who has studied obesity and asthma at St. Louis Children's Hospital, said a limitation of this and other studies is that it's not clear whether asthma was diagnosed with lung function tests.
Without those measures, he said, it's possible some kids were being treated for shortness of breath due to being obese and out of shape, and not true asthma.
"The results would be interesting, but I feel that it's incomplete because the characterization of how severe the asthma is really needs pulmonary function (measurements)," said Dr. Michelson, who wasn't involved in the new research.
"We need more data specifically about lung function to characterize these patients more definitively and to see if asthma and obesity are as definitively linked as we think."
"Having an actual quantitative measure of lung function would be ideal," Black said.
But, she added, "I don't think there's gross misclassification going on here."
Dr. Carlos Camargo, an epidemiologist from the Harvard School of Public Health in Boston who has also studied this topic, said the new report "confirms observations from several prior studies."
Camargo said in an email that in order to learn how to improve asthma control in people with the condition, and to prevent asthma in the first place, the next step will be to conduct more reliable trials, in which people are randomly assigned to different therapies.