Background: Obesity has been linked to respiratory symptoms and may decrease lung volume. However, rare large-scale study has been conducted to investigate the relationship between body mass index (BMI) and lung vital capacity (LVC) in Chinese adults.
 
Methods: This ongoing multi-centered study was approved (2021(E2)-KS-086) by the research ethics committees of The Affiliated Hospital of Hangzhou Normal University, Wuyunshan Hospital of Hangzhou and Hangzhou Women?s Hospital. Participants were recruited from the physique monitoring centers of the above institutes. We collected demographics and physical health data, and performed descriptive as well as regression analyses as appropriate. All regressions were adjusted for age and gender.
 
Results: From February 2021 to November 2022, a total of 3356 adults (mean age: 39.4 ± 10.2 yrs., female: 71.5%) participated. Their mean BMI was 23.1 ± 3.5 kg/m², mean LVC was 2.8 ± 0.8 L. Following the national physique monitoring standards, our subjects were classified as malnutrition (N= 225, 6.7%), with a lower BMI (N= 329, 9.8%), normal (N= 2241, 66.8%), overweight (N= 234, 7.0%) and obesity (N= 327, 9.7%). There was no significant linear relationship between BMI and LVC (r= -0.02, 95% CI -0.01 to 0.002, p= 0.18) among all the included individuals. While excluding those malnutrition and lower BMI ones, the relationship became statistically significant (r= -0.04, 95% CI -0.02 to -0.004, p= 0.002). When further narrowing to those obese ones the absolute value of the coefficient became even larger (r= -0.09, 95% CI -0.06 to -0.005, p= 0.02).

Conclusions: BMI has significant impacts on LVC of Chinese adults, especially for those obese ones with BMI ?28 kg/m².