The association between BMI and COPD: the results of two population-based studies in Guangzhou, China

An association between chronic obstructive pulmonary disease (COPD) and low body mass index (BMI) has been well established in cross-sectional studies. However, there have been few cohort studies investigating this issue. We therefore aimed to address this gap.

Two population-based studies, a cross-sectional study including 1818 subjects and a subsequent 4-year cohort study consisting of 759 individuals without COPD, were conducted in Guangzhou, China. Every subject was 40 years old or older at the time of recruitment and completed questionnaire interviews, anthropometric measurements and spirometry testing. As a follow-up, each subject underwent annual pre-bronchodilator spirometry testing. Subjects with a pre-bronchodilator FEV1/FVC <0.7 were required to undergo post-bronchodilator spirometry testing. Subjects with a post-bronchodilator FEV1/FVC <0.7 were diagnosed with COPD.

Compared to subjects with normal BMI (18.5 to 23.9 kg/m(2)), those with low BMI (<18.5 kg/m(2)) had a higher prevalence of COPD (21.1% vs. 7.5%), with an adjusted OR of 2.75 [95% confidence intervals (CI): 1.69 to 4.47]. Both low BMI and obese (≥ 28.0 kg/m(2)) subjects had lower FEV1 after adjustment. This association was further confirmed in the cohort study; non-COPD subjects with low BMI at baseline were more likely to develop COPD (RR = 2.88, 95% CI: 1.06 to 7.85), independent of smoking status and other confounders.

Low BMI was not only a systemic consequence of COPD but also an important risk factor for the development of COPD, which raises the possibility that early intervention in subjects with low BMI may reduce the incidence of COPD.