Effect of obesity on airway inflammation: a cross‐sectional analysis of body mass index and sputum cell counts

Abstract

Summary Background Several observational studies have demonstrated an association between obesity and asthma. Studies evaluating exhaled nitric oxide levels and obesity have revealed that a higher body mass index (BMI) is associated with elevated exhaled nitric oxide levels. Airway inflammation using sputum cell counts has not been assessed in obese patients with airway diseases. Objective The primary aim of this study was to determine whether obesity (based on BMI) is associated with eosinophilic or neutrophilic bronchitis. Methods The results from a database of induced sputum cell counts were compared with BMI and analysed using correlation statistics, regression and parametric and non‐parametric analysis. Results Seven‐hundred and twenty‐seven adult participants with an equal number of sputum samples were included in the analysis. BMI varied from 14.5 to 55 kg/m2. Sputum total cell count (mean±SD: 12.9 × 106 cell/g±21.5), eosinophil percent (median; min to max: 0.3%; 0–89.0), and neutrophil percent (mean±SD: 63.5±26.6%) were within normal limits. Participants with asthma had a higher percentage of sputum eosinophils than those without asthma (P=0.01). However, there was no difference in the total or differential cell counts among the obese and non‐obese participants, when the data were analysed according to BMI category, gender, dose of inhaled corticosteroid, and presence or absence of asthma. Conclusion In this large sample of adult asthmatic and non‐asthmatic participants, there was no association between BMI and airway inflammation measured by sputum cell counts. Other mechanisms to explain the relationship between obesity and asthma will need to be explored if this association is to be better understood.

Asthma symptoms in obese adults: The challenge of achieving asthma control

“…These findings, therefore, suggest a less favorable effect on airway inflammation of ICS in obese patients with asthma. In contrast to the study by Telenga et al [7], an association between obesity and eosinophilic airway inflammation has not been reported from previous studies [8][9][10].…”

Airway inflammation is augmented by obesity and fatty acids in asthma

“…IL-6 was negatively correlated with FEV1 and FVC (r s 5 -0.376, p,0.001 and r s 5 -0.515, p,0.001, respectively; n5112) and positively with ACQ score (r s 5 0.275, p50.003; n5111). In asthmatic subjects, males had a significantly higher IL-6 (median (IQR) 1.9 (1.3-3.0) versus 1.4 (1.1-2.4) pg?mL -1 ; p50.036), and reduced CRP (2.2 (0.9-5.6) versus 3.5 (1.3-9.6) mg?L -1 ; p50.069) and leptin (3,038 (2,055-5,906) versus 8,205 (3,199) pg?mL -1 ; p,0.001) compared with females.…”

“…Neutrophilic asthma involves innate immune dysfunction, with a persistence of symptoms and airway hyperresponsiveness (AHR) in the absence of sputum eosinophils [5]. Three recent studies reported no relationship between obesity and neutrophilic airway inflammation; however, all showed a clear nonsignificant trend towards increased sputum neutrophils as body mass index (BMI) increased [2][3][4]. The lack of statistical significance in these studies is possibly due to the small sample size in two studies [2,4], sex differences not being considered in two instances [2,3] and the large variation generally observed in the measurement of sputum cell counts.…”

“…Three recent studies reported no relationship between obesity and neutrophilic airway inflammation; however, all showed a clear nonsignificant trend towards increased sputum neutrophils as body mass index (BMI) increased [2][3][4]. The lack of statistical significance in these studies is possibly due to the small sample size in two studies [2,4], sex differences not being considered in two instances [2,3] and the large variation generally observed in the measurement of sputum cell counts. A recent cluster analysis performed by HALDAR et al [6] identified a unique obese-asthma phenotype: a population that is obese and predominantly female, with an absence of airway eosinophils.…”

“…Although the mechanism(s) responsible for the association remain unknown, a number of hypotheses, including inflammation, gastro-oesophageal reflux and mechanical factors, have been explored [1]. Researchers have examined the role of asthmatic airway inflammation and have found no relationship with obesity, measured directly via sputum eosinophils [2][3][4] or indirectly by exhaled nitric oxide [4]. This has led to the general consensus that airway inflammation is not driving the association between asthma and obesity.…”