The association between obesity and asthma: interactions between systemic and airway inflammation.

Rationale: Both obesity and asthma are common conditions, and both are characterized by the presence of inflammation. Animal studies suggest that the development of airway hyperresponsiveness with antigen challenge is exaggerated with obesity. However, clear evidence for either an additive or a synergistic pathologic interaction between obesity and asthma is lacking in humans.
Objectives: To identify whether an interaction between systemic and local inflammation occurs in obese subjects with asthma in a controlled observational study.
Methods: We studied 79 women: obese patients with asthma (n = 20), normal-weight patients with asthma (n = 19), obese patients without asthma (n = 20), and normal-weight patients without asthma (n = 20). After corticosteroid withdrawal, between-group differences in spirometric values, lung volumes, exhaled nitric oxide, induced sputum cell counts, and biomarkers of inflammation in sputum supernatant and blood were measured, and interactions explored.
Measurements and Main Results: Markers of systemic inflammation were increased with obesity, and Th2 cytokines were increased with asthma, but no important interactions were identified. Obesity adversely affected lung function with increases in functional residual capacity and residual volume in obese but not normal-weight patients with asthma, with a significant obesity by asthma interaction.
Conclusions: The link between obesity and asthma is unlikely to be explained by enhancement of the "classical" forms of airway inflammation resulting from the systemic inflammatory effects of obesity itself. Other mechanisms, possibly related to innate immunity, may explain the relationship between obesity and asthma.