Fatty tissue in the walls of airways alters their normal structure leading to inflammation which could cause wheezing and asthma, the study suggests.
Dr Peter Noble from the University of Western Australia, who co-authored the study, said: “Being overweight or obese has already been linked to having asthma or having worse asthma symptoms.
“Researchers have suggested that the link might be explained by the direct pressure of excess weight on the lungs or by a general increase in inflammation created by excess weight.”
Scientists looked at the structures of 1,373 airways inside the lungs of dead people who had donated their bodies for research. They studied the lungs from 52 individuals, including 15 who did not have asthma, 21 who had asthma but died of other causes and 16 who died of asthma.
They found accumulation of fatty tissue inside the lungs correlated with the body weight of individuals, according to the paper published in the European Respiratory Journal.
Dr Noble said: “We’ve found that excess fat accumulates in the airway walls where it takes up space and seems to increase inflammation within the lungs.
“We think this is causing a thickening of the airways that limits the flow of air in and out of the lungs, and that could at least partly explain an increase in asthma symptoms.”
Researchers are now looking for new ways to study fatty tissue in the lungs.
Professor Thierry Troosters, president of the European Respiratory Society, who was not involved in the study, said: “This is an important finding on the relationship between body weight and respiratory disease because it shows how being overweight or obese might be making symptoms worse for people with asthma.
“This goes beyond the simple observation that patients with obesity need to breathe more with activity and exercise hence adding to their ventilatory burden. The observation points at true airway changes that are associated with obesity.
“We need to investigate this finding in more detail and particularly whether this phenomenon can be reversed with weight loss.
“In the meantime, we should support asthma patients to help them achieve or maintain a healthy weight.”
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