New US research has found that children who have asthma are more likely to become obese than children who don't.
Carried out by the University of Southern California, a team of researchers looked at the records of 2,171 Southern California children aged 5 to 8 who enrolled in the Children's Health Study, one of the largest and most detailed studies on the long-term effects of air pollution on the health of children.
None of the children were obese when they enrolled in the study, but 13.5 percent had asthma.
The students were followed for up to 10 years, during which time 15.8 percent of the children became obese.
The researchers found that children with asthma were 51 percent more likely to become obese over the next decade compared to children who did not have asthma, but children who used asthma inhalers when they had an attack were 43 percent less likely to become obese.
"Children who have asthma are often overweight or obese, but the scientific literature has not been able to say asthma causes obesity," commented Zhanghua Chen, lead author of the study, "However, our study and that of others support the finding that having asthma in early childhood may lead to increased risk of childhood obesity."
One of the reasons put forward for the link between asthma and obesity is that respiratory problems may cause asthmatic children to play and exercise less, however this study did account for physical activity.
Commenting on the importance of the findings, Frank Gilliland, senior author of the study, explained that elevated asthma and obesity levels may contribute to the development of other metabolic diseases, including prediabetes and Type 2 diabetes in later life, and that early diagnosis and treatment of asthma is important to help try to prevent the childhood obesity epidemic.
"Part of the problem may be a vicious cycle where asthma and obesity negatively affect each other," he added, "Our results also suggest that asthma inhalers may help prevent obesity in children. Although this observation warrants further study, it is interesting that the correlation exists irrespective of physical activity and other asthma medication use."
The study did have some limitations however. The researchers used self-reported questionnaires which can be inaccurate, had limited information on exercise, and also didn't collect data about the students' diets.
The study can be found published in the American Journal of Respiratory and Critical Care Medicine.