Researchers have found that fatty tissues accumulate in the airway walls, particularly in people who are overweight or obese.

The study, published in the European Respiratory Journal, suggested that the fatty tissue alters the structure of people's airways and this could be one reason behind the increased risk of asthma. "Our research team studies the structure of the airways within our lungs and how these are altered in people with respiratory disease," said the study's author John Elliot from Sir Charles Gairdner Hospital in Australia. "Looking at the samples of lungs, we spotted fatty tissue that had built up in the airway walls. We wanted to see if this accumulation was correlated with body weight," Elliot said.

The researchers examined post-mortem samples of the lungs that had been donated for the research and stored in the Airway Tissue Biobank. They studied samples from 52 people, including 15 who had no asthma, 21 who had the disease but died of other causes and 16 who died of asthma. Using dyes to help visualise the structures of 1373 airways under a microscope, they identified and quantified any fatty tissue present.

They compared this data with each person's body mass index (BMI). The study showed that fatty tissue accumulates in the walls of the airways. The analysis revealed that the amount of fat present increases in line with increasing BMI. "We've found that excess fat accumulates in the airway walls where it takes up space and seems to increase inflammation within the lungs," said the study's co-author Peter Noble. "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," Noble said.