Objective: To investigate the correlation between body mass index (BMI) and chronic obstructive pulmonary disease (COPD), based on a cross-sectional COPD survey conducted in Beijing, Shanghai, Guangdong, Liaoning, Tianjin, Chongqing and Shaanxi of China between 2002-2004.
Methods: A multi-stage stratification cluster sampling strategy was used in this cross-sectional survey, and 20,245 subjects (8705 males and 11,540 females) aged 40 years or older were recruited, interviewed with a questionnaire, measured for height and weight, and tested with spirometry. 1668 subjects with post-bronchodilator FEV1/FVC less than 70% were identified as having COPD after other known causes of airflow limitation were excluded. Analysis on relationship between COPD and BMI was performed in 1668 COPD and 18 577 non-COPD subjects.
Results: Compared with non-COPD subjects, BMI was significantly lower in COPD patients [(22.7+/-3.5) vs (24.1+/-3.4) kg/m2, F=158.31, P<0.01]; BMI was also significantly lower in smokers than in non-smokers [(23.6+/-3.4) vs (24.2+/-3.5) kg/m2, F=49.10, P<0.01]. And an addictive interaction to BMI between COPD and smoking was observed (F=6.03, P<0.05). BMI decreased with the increase of the stage of COPD (F=45.6, P<0.01), with a negative relationship (r=-0.08, P<0.01). Lower BMI was significantly associated with increased risk of COPD (chi2=102.68, P<0.01). Compared with subjects with normal BMI (BMI=24.0-27.9 kg/m2), those with lower BMI (BMI<18.5 kg/m2) were more likely to have COPD [adjusted OR=2.12 (95% CI 1.73-2.59)], while those with higher BMI (BMI=24.0-27.9 kg/m2) and obesity (BMI>or=28.0 kg/m2) were less likely to have COPD [adjusted OR=0.67 (95% CI 0.59-0.76); and 0.60 [(95% CI 0.49-0.73), respectively]. Moreover, there was an interaction to COPD between smoking and BMI (chi2=4.73, P<0.05). Compared with COPD patients with normal BMI, the quality of life in those with lower BMI was impaired (55+/-8 vs 57+/-6 in mental scores of SF-12, F=2.96, P<0.05; 42+/-10 vs 46+/-9 in physical scores of SF-12, F=4.21, P<0.01), and their dyspnea scores were higher (1.4+/-1.5 vs 1.1+/-1.3, chi2=14.32, P<0.01).
Conclusion: Lower BMI was strongly associated with COPD, possibly as a risk factor for COPD independent of smoking, and a potential predictor for COPD severity.