The incidence of asthma and obesity is increasing worldwide, and reports suggest that obese patients have more severe asthma. We investigated whether obese asthma patients have more severe airway obstruction and airway hyper-responsiveness and a different type of airway inflammation than lean asthmatics. Furthermore, we assessed the effect of obesity on corticosteroid treatment response.

Patient data from four well-documented asthma cohorts were pooled (n = 423). We evaluated FEV₁, bronchial hyper-responsiveness (PC₂₀) to either methacholine/histamine or adenosine 5′-monophosphate (AMP) (differential) cell counts in induced sputum and blood and corticosteroid treatment response in 118 patients.

At baseline, FEV₁, PC₂₀ methacholine or histamine, and PC₂₀AMP values were comparable in 63 obese (BMI ≥30 kg/m²) and 213 lean patients (BMI <25 kg/m²). Obese patients had significantly higher blood neutrophils. These higher blood neutrophils were only seen in obese women and not in obese men. After a two-week treatment with corticosteroids, we observed less corticosteroid-induced improvement in FEV₁%predicted in obese patients than in lean patients (median 1.7% vs 6.3% respectively, P = 0.04). The percentage of sputum eosinophils improved significantly less with higher BMI (P = 0.03), and the number of blood neutrophils increased less in obese than in lean patients (0.32 x10³/μl vs 0.57 x10³/μl, P = 0.046).

We found no differences in asthma severity between obese and nonobese asthmatics. Interestingly, obese patients demonstrated more neutrophils in sputum and blood than nonobese patients. The smaller improvement in FEV₁ and sputum eosinophils suggests a worse corticosteroid treatment response in obese asthmatics.