Study Explores Asthma, Obesity, Work Ability, and Lung Function Associations

plexus lung illustration
Are asthma and increased BMI independently linked to respiratory health outcomes, and is there a possible interaction between asthma and BMI?

A cross-sectional Norwegian population study explored connections between asthma and increased body mass index (BMI), as well as the extent to which these 2 conditions were independently associated with lung function, respiratory symptoms, Work Ability Score, and sick leave. Results of the study, which ultimately found little connection between asthma and increased BMI, were published in BMJ Open Respiratory Research.

In the study, “obese” was defined as BMI of 30 kg/m2 or more; “overweight” as 25 to 29 kg/m2; and “normal weight” as BMI less than 25 kg/m2.  Researchers analyzed data from 626 patients with physician-diagnosed asthma (127 obese, 255, overweight, and 309 normal weight) and 691 individuals without asthma (168 obese, 230 overweight, and 228 normal weight). All participants underwent examinations, completed spirometry testing, and filled out a questionnaire. Associations between asthma, BMI, and outcome variables were assessed via regression models adjusted for sex, age, education, and smoking status.

Participants with asthma and obesity had an older age at symptom onset (mean, 16.6 years), more often used asthma medications (65%), and exhibited poorer control of their asthma, with 43% reporting an Asthma Control Test score of 5 to 19. Additionally, the participants with asthma more often reported other respiratory conditions, such as respiratory allergy, compared with the healthy controls. 

Results of the study showed that asthma was associated with increased symptom scores (odds ratio [OR], 7.3; 95% CI, 5.5 to 9.7), decreased Work Ability Score (OR, 1.9; 95% CI, 1.4 to 2.5), and increased sick leave over the past 12 months (OR, 1.4; 95% CI, 1.1 to 1.8). Further, obesity was linked to increased symptom scores (OR, 1.7; 95% CI, 1.2 to 2.4).

Regarding respiratory outcomes, asthma was associated with reduced rebronchodilator forced expiratory volume in 1 second (FEV1) and postbronchodilator FEV1 (95% CI, –8.2 to –5.1 and 95% CI, –6.7 to –3.4, respectively). Asthma was also associated with prebronchodilator forced vital capacity (FVC; 95% CI, –3.6 to –0.96). Additionally, obesity was linked to decreased prebronchodilator and postbronchodilator FEV1 (95% CI, –5.1 to –0.7 and 95% CI, –4.9 to –0.7, respectively), as well as to decreased rebronchodilator and postbronchodilator FVC (95% CI, –7.0 to –3.4 and 95% CI, –6.1 to –2.3, respectively).

The only significant interaction reported between asthma and overweight status was for prebronchodilator FVC (95% CI, –6.6 to –0.6). Aside from this apparent additive interaction on reduced prebronchodilator FVC, no other significant additive or multiplicative interactions between asthma and overweight status (as assessed by body BMI), were observed.

The investigators concluded that because of the small number of participants with BMIs of 35 kg/m2  or more who were enrolled in the current study, additional research in this subpopulation is warranted.


Klepaker G, Henneberger PK, Hertel JK, Holla ØL, Kongerud J, Fell AKM. Influence of asthma and obesity on respiratory symptoms, work ability and lung function: findings from a cross-sectional Norwegian population study. BMJ Open Respir Res. 2021;8(1):e000932. doi: 10.1136/bmjresp-2021-000932