Impact of Body Mass Index Change on the Prognosis of Chronic Obstructive Pulmonary Disease

<b><i>Background:</i></b> Low body mass index (BMI) is an important prognostic factor in chronic obstructive pulmonary disease (COPD). However, the prognostic value of longitudinal BMI change in COPD has not been well studied. <b><i>Objective:</i></b> We aimed to evaluate the association between longitudinal change of BMI and prognosis of COPD in Korean COPD cohort. <b><i>Methods:</i></b> This study was conducted in a prospective Korean Obstructive Lung Disease (KOLD) cohort where COPD patients were recruited on an outpatient basis at 17 hospitals in South Korea. Annual BMI was measured over a period of 3 years or more. All patients were categorized into underweight (UW), normal weight (NW), and overweight (OW) groups by BMI. Clinical characteristics and outcomes including exacerbation and mortality were compared based on initial BMI grade and longitudinal change of BMI. <b><i>Results:</i></b> This analysis included 537 COPD patients (mean age = 67.4 ± 7.9 years, male = 97.0%, mean BMI = 23.0 ± 3.1) of KOLD cohort. The proportions of UW, NW, and OW groups were 6.9% (<i>n</i> = 37), 68.9% (<i>n</i> = 370), and 24.2% (<i>n</i> = 130) respectively. The UW group showed lower forced expiratory volume in 1 s (FEV₁) (<i>p</i> &#x3c; 0.001), shorter 6-minute walk distance (<i>p</i> &#x3c; 0.001), higher modified Medical Research Council score (<i>p</i> = 0.002), higher St. George Respiratory Questionnaire score (<i>p</i> &#x3c; 0.001), higher emphysema index (<i>p</i> &#x3c; 0.001) and air-trapping index (<i>p</i> &#x3c; 0.001), and more frequent (<i>p</i> &#x3c; 0.001) and severe exacerbations (<i>p</i> = 0.003). Multivariable analyses demonstrated that decrease of BMI (hazard ratio [HR] = 0.786, <i>p</i> = 0.038) and the descent of BMI group (HR = 3.167, <i>p</i> = 0.016) at 3-year follow-up along with age, initial BMI, post-bronchodilator FEV₁, and severe exacerbations were significantly associated with mortality. <b><i>Conclusions:</i></b> This study demonstrated that BMI decrease during follow-up was independently associated with exacerbation and higher mortality of COPD, suggesting BMI reduction in COPD should be carefully managed.