By Nicole MacKee
Obesity may be responsible for as many as one in four cases of childhood asthma, according to US researchers, but an Australian expert warns that the jury remains out on causality.
Associate Professor Paul Robinson, Paediatric Respiratory Physician at The Children’s Hospital at Westmead, Sydney, said an association between obesity and asthma, in both directions, had been found in several studies and in different populations.
‘This study reports that early obesity is associated with later asthma [in children], but it doesn’t prove causality,’ he said.
The retrospective cohort study, published in Pediatrics, evaluated data from more than 500,000 children aged 2 to 17 years.
After a mean observation period of four years, the researchers estimated that 23 to 27% of new asthma cases in children with obesity were directly attributable to the obesity.
Asthma incidence was defined as two or more clinical encounters with a diagnosis of asthma and one or more prescriptions for asthma controller medications. When asthma diagnoses were confirmed with spirometry, the association between obesity and asthma risk remained, the researchers said.
‘Obesity is a major preventable risk factor for pediatric asthma,’ they concluded. The researchers estimated that, in the absence of overweight and obesity, 10% of all cases of asthma would be avoided.
Professor Lisa Wood of the University of Newcastle’s School of Biochemistry and Pharmacy said the US analysis was robust, and the results were not surprising.
‘It is well established that, in adults, obesity precedes the development of asthma in many individuals,’ she said.
Professor Wood said the mechanisms linking obesity and asthma were not clearly defined but were likely to be multifactorial.
‘Excess adipose tissue surrounding the chest wall causes mechanical restriction,’ Professor Wood said. ‘Obesity also causes immune dysfunction, as adipose tissue is biologically active and releases proinflammatory mediators into the blood stream, which have been linked to heightened airway inflammation.’
Further metabolic abnormalities associated with obesity, including insulin resistance and dyslipidaemia, had been linked to paediatric asthma, she said.
Associate Professor Robinson said it was important to conduct intervention studies to discover if a reduction in obesity rates would lead to a reduction in the incidence of asthma in children.
‘Modifiable risk factors for asthma are of great interest, but studies have yet to show that reducing obesity translates to true asthma prevention. We eagerly await those,’ he said. ‘But we can feel confident that if we reduce obesity rates, we are likely to have beneficial effects across a number of health outcomes for those children, including respiratory health.’
Pediatrics 2018; 142: e20182119.