The researchers have found that glucocorticoids, commonly known as steroids, the primary controller medication for asthma, are 40 percent less beneficial for overweight and obese asthma patients.
"These findings should spur doctors to carefully evaluate response to treatment in overweight and obese asthmatics and consider optimizing therapeutic regimens as indicated," said Associate Professor of Medicine E. Rand Sutherland, MD, MPH
"We also hope they will spur additional research into the treatment of obese patients with asthma,"
The researchers have also identified a mechanism that can be a potential target for development of new therapies.
Previous studies have shown that being overweight or obese increases the risk of asthma onset and makes it more difficult to control.
During the study, the researchers enrolled 45 non-smoking adults, 33 of whom had asthma, and measured the response of cells in the blood and the lungs to the steroid dexamethasone.
Steroids interfere with inflammatory signalling pathways by raising the level of a molecule known as MAP kinase phosphatase-1 (MKP-1). When the researchers applied the steroid dexamethasone to cultures of the participants' blood cells, they found that steroids did not increase MKP-1 as effectively in overweight and obese asthmatics when compared to lean asthmatics.
The study showed that dexamethasone increased the levels of MKP-1 by 5.27 times in cultured blood cells from lean asthma patients, whereas the molecule levels in overweight and obese asthmatics increased by only 3.11 times, a 41 percent smaller response.
The heavier a person was the less their cells were likely to respond to dexamethasone.
"Steroids were clearly less effective in overweight and obese asthma patients," said Sutherland.
"Previous studies have suggested a link between weight and response to steroids in patients, and this study suggests a potential mechanism by which this occurs. It also suggests that future research should be directed specifically to understanding how asthma medications work in overweight and obese asthmatics.
The study appears in October 1 issue of the American Journal of Respiratory and Critical Care Medicine.