"We were disappointed not to find a 'smoking gun' that would explain the common association between obesity and asthma," lead researcher Dr. D. Robin Taylor of the University of Otago in New Zealand. "We hypothesized that the low-grade systemic inflammation present in obesity would augment the inflammation of asthma -- a synergistic effect -- or alternatively, that the inflammation of obesity might affect the airways independently, perhaps resulting in mixed airway inflammation."

The researchers recruited 79 women -- 20 who were obese with asthma, 19 who were of a normal weight with asthma, 20 who were obese but who did not have asthma and 20 controls.

Asthmatics were told to stop using their anti-inflammatory inhaler for four weeks and then subjects underwent blood tests and tests for biomarkers of systemic and airway inflammation, such as C-reactive protein and cytokines in blood and inflammatory cells and cytokines in sputum.

The study, published in the September issue of the American Journal of Respiratory and Critical Care Medicine, found was that although inflammatory cells and other biomarkers of inflammation were increased, there was no significant interaction demonstrated between obesity and asthma.