Obesity does not worsen asthma in patients with mild and moderate forms of the disease, but it reduces the response to medications, suggests a study conducted by National Jewish Health researchers.
E. Rand Sutherland, an associate professor of Medicine at National Jewish Health who led the study, said: "With both asthma and obesity on the rise in recent years, there has been much interest in the possible link between these two conditions."
He further said: "By studying a well characterized group of patients with asthma, we were able to determine that increased weight is not associated with more severe asthma. Although benefits can be obtained with weight loss in other diseases, these findings suggest that an improvement in asthma may not necessarily result from weight loss."
He added: "The findings also suggest that patients and physicians should be aware that obese asthma patients may not respond well to corticosteroids, the most successful controller medication for asthma, which can affect dosing decisions and choices of possible alternatives to steroids."
While earlier studies have linked obesity with asthma risk, the exact mechanism for these links has been unclear.
The researchers decided to examine the issue in a well-characterised group of 1,256 patients who had participated in NIH-sponsored studies.
They divided them into patients with a body mass index of less than 25 (lean) and greater than or equal to 25 (overweight and obese).
It was found that lean asthma patients had slightly greater forced expiratory volume in one second, or FEV1, and slightly greater ratio of FEV1 to forced vital capacity, both common measures of lung function.
They also found slightly greater use of rescue inhalers among overweight patients and slightly higher scores asthma-relate quality of life questionnaires.
"These differences were small and are unlikely to be of any real clinical significance," said Sutherland.
However, response to medications did show an effect of increased weight.
Among a subgroup of 183 people, lean patients taking inhaled corticosteroids alone showed a 55 percent greater reduction in exhaled nitric oxide-a measure of inflammation.
Lean patients taking a combination inhaled steroid and long-acting beta agonist increased their FEV1 by 80 more millilitres, while there were no differences between these patients in the number of asthma exacerbations.
"The data suggest overweight and obese people respond less well to controller medications for asthma than do their lean counterparts," said Sutherland.
The study appears in the Journal of Allergy and Clinical Immunology.