Exploring the obesity-asthma link: do all types of adiposity increase the risk of asthma?

Background: Obesity and risk of asthma are linked. Different distributions of adiposity, such as visceral, subcutaneous or ectopic adiposity, may affect asthma risk differently.

Objective: To explore the association of different adiposity types with self-reported asthma, bronchial inflammation and lung function, accounting for possible effect modifiers, such as atopy and gender.

Methods: In a general population sample of 3471 persons aged 19-72, visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) were measured by ultrasound, and fat percentage by bio-impedance. Body mass index, waist circumference, waist-to-hip ratio (WHR), bronchial inflammation as fractional expiratory nitric oxide (FeNO), lung function [FEV(1) and forced vital capacity (FVC)], and atopy (specific IgE) were measured.

Results: All adiposity measures were associated with a higher risk of asthma. The risk estimates (odds ratios, OR, with 95% confidence interval, CI) of current asthma were of similar magnitude for all six adiposity measures ranging between 1.17, CI = 0.98-1.40 (SAT) and 1.51, CI = 1.17-1.95 (WHR). The adiposity-asthma associations were significantly stronger in non-atopics than in atopics. In non-atopics the risk estimates of current asthma ranged between 1.35 CI = 1.08-1.72 and 1.82 CI = 1.34-2.46 for SAT and WHR respectively. Consistent results were obtained using dichothomized adiposity measures (obese vs. non-obsese). The FVC and FEV(1) decreased significantly with increasing adiposity in both atopics and non-atopics, e.g. FVC decreased between 36 mL (CI = 10, 62 mL) and 155 mL (CI = 124, 186 mL) for one unit (standard error) increase of SAT and VAT respectively. Adiposity measures were not associated with atopy and not consistently associated with FeNO levels.

Conclusions and clinical relevance: The effect of adiposity on asthma was mainly seen in non-atopics and did not appear to depend on the distribution of adiposity as reflected by the adiposity measures used in the present study. Increasing adiposity was associated with lower lung function independent of atopic status.