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Obesity and Asthma^*

A Specific Phenotype?

^* From the Centre de Recherche, Hôpital Laval, Institut de cardiologie et de pneumologie de l’Université Laval, Québec, QC, Canada.

Correspondence to: Louis-Philippe Boulet, MD, FCCP, Hôpital Laval, 2725 Chemin Sainte-Foy, Québec, QC Canada, G1V 4G5; e-mail: lpboulet{at}med.ulaval.ca

Abstract

Background: Obesity is associated with an increased prevalence of asthma, especially in women, and appears to be more severe in the obese. This study aimed to determine if obese subjects have a specific asthma phenotype.

Methods: Forty-four consecutive obese subjects (body mass index [BMI] 30 kg/m²) and 44 consecutive nonobese subjects (BMI < 25 kg/m²), all with asthma, completed an asthma control questionnaire, and underwent methacholine challenge with symptom perception scores, and sputum induction for differential cell count. BMI, waist circumference, and waist-to-hip ratio also were measured.

Results: Despite similar expiratory flows, bronchodilator response, airway responsiveness to methacholine, and symptom perception scores, asthma control was poorer in obese subjects than in nonobese subjects (p = 0.005). Total lung capacity (p = 0.01), expiratory reserve volume (p < 0.0001), functional residual capacity (p < 0.0001), and residual volume (p = 0.006) were lower in obese subjects than in nonobese subjects. Induced-sputum eosinophil and neutrophil counts were similar in both groups, although there was an inverse correlation between sputum eosinophils and waist circumference and a trend for a similar relationship for BMI. Blood serum C-reactive protein (p = 0.009) and fibrinogen (p = 0.0004) levels were higher in obese subjects than in nonobese subjects.

Conclusion: Obese people with asthma had poorer asthma control than nonobese asthmatics despite similar symptoms perception. Bronchial and systemic inflammatory characteristics and the specific pattern of pulmonary function changes suggest a different phenotype of asthma in these subjects.

Trial registration: Clinicaltrials.gov Identifier: NCT00532363 [ClinicalTrials.gov] and NCT00532831 [ClinicalTrials.gov] .

Key Words: asthma • asthma control • body mass index • inflammatory markers • lung function • obesity • sputum induction • symptom perception