The association of two different measures of body habitus with lung function: a population-based study.

Background: The relation between obesity and respiratory function is complex and may be confounded by other components of body habitus such as lean muscle mass. The present study aimed to explore the association between two different measures of body habitus (Body Mass Index - BMI, and lean muscle mass) with lung function.

Methods: We used data from 2663 adults who participated in a community-based survey and provided measures of lung function, BMI and 24-h urinary creatinine excretion to quantify lean muscle mass.

Results: There was a positive linear association between 24-h urinary creatinine excretion and lung function as measured by both Forced Expiratory Volume in 1 s (FEV(1)) and Forced Vital Capacity. A one standard deviation increment in 24-h urinary creatinine excretion was associated with a 45 ml increase in FEV(1) (95% confidence intervals CI: +16 to +73). There was no linear association between body mass index and lung function although those in the extreme categories of BMI had lower measures of lung function compared to a reference group with a BMI of 20-24.9 kg/m(2). For FEV(1), BMI less than 20 kg/m(2) was 122 ml lower (95% CI: -234 to -10); BMI greater than 30 kg/m(2) was 85 ml lower (95% CI: -160 to -9).

Conclusions: Lean muscle mass and BMI have very different associations with lung function that have implications for understanding the relationship between body habitus and lung function.