Associations between lung function and physical and cognitive health in the Canadian Longitudinal Study on Aging (CLSA): A cross-sectional study from a multicenter national cohort

Background
Low lung function is associated with high mortality and adverse cardiopulmonary outcomes. Less is known of its association with broader health indices such as self-reported respiratory symptoms, perceived general health, and cognitive and physical performance. The present study seeks to address the association between forced expiratory volume in 1 second (FEV1), an indicator of lung function, with broad markers of general health, relevant to aging trajectory in the general population.

Methods and findings
From the Canadian general population, 22,822 adults (58% females, mean age 58.8 years [standard deviation (SD) 9.6]) were enrolled from the community between June 2012 and April 2015 from 11 Canadian cities and 7 provinces. Mixed effects regression was used to assess the cross-sectional relationship between FEV1 with self-reported respiratory symptoms, perceived poor general health, and cognitive and physical performance. All associations were adjusted for age, sex, body mass index (BMI), education, smoking status, and self-reported comorbidities and expressed as adjusted odds ratios (aORs). Based on the Global Lung Function Initiative (GLI) reference values, 38% (n = 8,626) had normal FEV1 (z-scores >0), 37% (n = 8,514) mild (z-score 0 to > −1 SD), 19% (n = 4,353) moderate (z-score −1 to > −2 SD), and 6% (n = 1,329) severely low FEV1 (z-score = < −2 SD). There was a graded association between lower FEV1 with higher aOR [95% CI] of self-reported moderate to severe respiratory symptoms (mild FEV1 1.09 [0.99 to 1.20] p = 0.08, moderate 1.45 [1.28 to 1.63] p < 0.001, and severe 2.67 [2.21 to 3.23] p < 0.001]), perceived poor health (mild 1.07 [0.9 to 1.27] p = 0.45, moderate 1.48 [1.24 to 1.78] p = <0.001, and severe 1.82 [1.42 to 2.33] p < 0.001]), and impaired cognitive performance (mild 1.03 [0.95 to 1.12] p = 0.41, moderate 1.16 [1.04 to 1.28] p < 0.001, and severe 1.40 [1.19 to 1.64] p < 0.001]). Similar graded association was observed between lower FEV1 with lower physical performance on gait speed, Timed Up and Go (TUG) test, standing balance, and handgrip strength. These associations were consistent across different strata by age, sex, tobacco smoking, obstructive, and nonobstructive impairment on spirometry. A limitation of the current study is the observational nature of these findings and that causality cannot be inferred.

Conclusions
We observed graded associations between lower FEV1 with higher odds of disabling respiratory symptoms, perceived poor general health, and lower cognitive and physical performance. These findings support the broader implications of measured lung function on general health and aging trajectory.