Reverse J-shaped relationship between body mass index and in-hospital mortality of patients hospitalized for heart failure in Japan

Several lines of evidence demonstrated body mass index (BMI) to be inversely associated with outcomes of patients with HF, so-called obesity paradox. However, the relationship between BMI and outcomes of patients with HF in Japan has been poorly understood. This study sought to explore the relationship between BMI and in-hospital mortality of patients hospitalized for heart failure (HF) in Japan and whether BMI at hospital admission could be used for the risk stratification of hospitalized HF patients. We studied 407,722 patients hospitalized for HF between January 2010 and March 2018, using the Diagnosis Procedure Combination database, a national inpatient database in Japan. Patients were categorized into four groups: underweight (BMI < 18.5 kg/m(2)), 66,342 patients (16.3%); normal (18.5-24.9 kg/m(2)), 240,801 patients (59.1%); pre-obesity (25.0-29.9 kg/m(2)), 76,954 patients (18.9%); and obesity (>= 30.0 kg/m(2)), 23,625 patients (5.8%). Pre-obese and obese patients were younger and more likely to be male. Advanced HF symptoms were more common among underweight patients. Multivariable logistic regression analysis fitted with generalized estimating equation showed that, compared with normal weight patients underweight patients had higher in-hospital mortality (odds ratio 1.50, 95% confidence interval 1.45-1.55), whereas pre-obese patients (odds ratio 0.80, 95% confidence interval 0.77-0.83) and obese patients (odds ratio 0.90, 95% confidence interval 0.84-0.97) had lower in-hospital mortality. Restricted cubic spline showed a reverse J-shaped relationship between BMI and in-hospital mortality with the bottoms of splines around BMI 26 kg/m(2). In conclusion, underweight patients had higher, and pre-obese and obese patients had lower in-hospital mortality compared to patients with normal weight patients. Furthermore, restricted cubic spline indicated a reverse J-shaped relationship between BMI and in-hospital mortality. Our findings are informative for the risk stratification of patients hospitalized for HF according to BMI.