Childhood obesity and asthma are often found to occur together, but existing research has not yet clarified whether asthma actually contributes to the childhood obesity "epidemic."
New research from the University of Southern California (USC) in Los Angeles aims to fill this research gap by examining the effects of asthma and asthma medication on childhood obesity.
The findings were published in the American Journal of Respiratory and Critical Care.
Assessing the link between early-life asthma and childhood obesity
The researchers - led by Zhanghua Chen, a research associate of environmental health at the Keck School of Medicine at USC - examined the medical records of 2,171 non-obese children between 5-8 years old.
These children were enrolled in the Southern California Children's Health Study (CHS) and were clinically followed for 10 years.
CHS is a large-scale, long-term, detailed study of the lasting effects of air pollution on the respiratory and metabolic health of children.
The USC researchers examined 10 years' worth of data collected in the CHS, and they also performed a replication analysis on an independent sample of 2,684 CHS children. This latter cohort was followed from the average age of 9.7 years to 17.8 years.
During this time, researchers measured the children's height and weight annually, categorizing them into normal, overweight, and obese. Children were deemed overweight or obese if their body mass index (BMI) was at or above the 85th and 95th percentile, respectively, compared with the BMI standards set by the CDC.
Chen and team assessed the children's asthma using the physician's diagnosis as reported by the children or by their parents.
The parents also filled in complex questionnaires on sociodemographic factors and smoking exposure at home or in utero, as well as physical activity patterns and history of respiratory illness.
The scientists used Cox regression to evaluate the associations between asthma and the incidence of obesity during the follow-up period.
Children with asthma 51 percent more likely to become obese
At the beginning of the study, over 18 percent of the children were overweight and over 13 percent had been diagnosed with asthma.
During the follow-up period, 15.8 percent of children developed obesity.
After statistical adjustments, the researchers found that early childhood asthma did contribute to the development of obesity in subsequent years, mainly during early childhood and adolescence.
Compared with non-obese, asthma-free children, the non-obese children who did have asthma were 51 percent more likely to develop obesity during follow-up. The results stayed the same following sociodemographic adjustments and adjustments for other variables.
Additionally, children with a history of wheezing were at a 42 percent higher risk of developing obesity.
The age of asthma onset did not seem to influence the obesity risk.
Regarding the link between the use of asthma medications and obesity, the researchers made another interesting discovery. They found that the use of asthma rescue medications, such as an asthma inhaler, significantly lowered the risk of obesity. These results were independent of physical activity.
Significance of the study
The authors note that theirs is one of the few studies to link early-life asthma with an increased risk of developing obesity.
Some of the study's limitations include the fact that the information was self-reported, and that the scientists did not have access to sufficient information regarding diet or physical activity patterns.
Frank Gilliland, the study's senior author, points out that a combination of asthma and obesity can trigger other metabolic diseases in adulthood, including prediabetes and type 2 diabetes.
"Children who have asthma are often overweight or obese, but the scientific literature has not been able to say asthma causes obesity," adds Chen.
"However, our study and that of others support the finding that having asthma in early childhood may lead to increased risk of childhood obesity," he notes.
Although it could be that the respiratory problems prevent children with asthma from playing and exercising as much as healthy children, it is interesting, the authors note, that this study accounted for physical activity yet still showed these results.
"Early diagnosis and treatment of asthma may help prevent the childhood obesity epidemic. Part of the problem may be a vicious cycle where asthma and obesity negatively affect each other. 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."
Effects of childhood asthma on the development of obesity among school-aged children, Zhanghua Chen et al., American Journal of Respiratory and Critical Care, doi: abs/10.1164/rccm.201608-1691OC, published online 19 January 2017, abstract.
USC news release, accessed 20 January 2017 via EurekAlert.
Additional source: American Academy of Allergy Asthma and Immunology, Asthma statistics, accessed 20 January 2017.
Additional source: CDC, Childhood obesity statistics, accessed 20 January 2017.