Paradoxical association between body mass index and in-hospital mortality in elderly patients with chronic obstructive pulmonary disease in Japan

Background and objective: The prevalence and mortality of chronic obstructive pulmonary disease (COPD) in elderly patients are increasing worldwide. Low body mass index (BMI) is a well-known prognostic factor for COPD. However, the obesity paradox in elderly patients with COPD has not been well elucidated. We investigated the association between BMI and in-hospital mortality in elderly COPD patients. Methods: Using the Diagnosis Procedure Combination database in Japan, we retrospectively collected data for elderly patients (>65 years) with COPD who were hospitalized between July 2010 and March 2013. We performed multivariable logistic regression analysis to compare all-cause in-hospital mortality between patients with BMI of <18.5 kg/m(2) (underweight), 18.5-22.9 kg/m(2) (low-normal weight), 23.0-24.9 kg/m(2) (high-normal weight), 25.0-29.9 kg/m(2) (overweight), and >= 30.0 kg/m(2) (obesity) with adjustment for patient backgrounds. Results: In all, 263,940 eligible patients were identified. In-hospital mortality was 14.3%, 7.3%, 4.9%, 4.3%, and 4.4%, respectively, in underweight, low-normal weight, high-normal weight, overweight, and obese patients. Underweight patients had a significantly higher mortality than low-normal weight patients (odds ratio [OR]: 1.55, 95% confidence interval [CI]: 1.48-1.63), whereas lower mortality was associated with high-normal weight (OR: 0.76, CI: 0.70-0.82), overweight (OR: 0.73, CI: 0.66-0.80), and obesity (OR: 0.67, CI: 0.52-0.86). Higher mortality was significantly associated with older age, male sex, more severe dyspnea, lower level of consciousness, and lower activities of daily living. Conclusion: Overweight and obese patients had a lower mortality than low-normal weight patients, which supports the obesity paradox.