Impact of body mass index on in-hospital mortality in older patients hospitalized for bacterial pneumonia with non-dialysis-dependent chronic kidney disease

BACKGROUND: Low body mass index (BMI) in older individuals with decreased kidney function is important because of its association with poor prognosis and frailty. Herein, we aimed to clarify the association between BMI and in-hospital mortality among older patients with non-dialysis-dependent chronic kidney disease (CKD) stratified by kidney function. METHODS: Using data from the Medical Vision Database, this multicentre cohort study included people aged ≥ 60 years with an estimated glomerular filtration rate of < 60 ml/min/1.73 m(2) but without dialysis dependency, hospitalised for bacterial pneumonia during 2014–2019. We compared the risk of in-hospital death between patients with BMI categories based on the quartiles (low, medium–low, medium–high, and high) setting medium–high BMI as a reference. We further assessed the association with BMI using a cubic spline, setting BMI as a nonlinear continuous variable and a BMI of 22 kg/m(2) as a reference. We also evaluated the association between BMI and kidney function using a generalised additive model adjusted for interaction terms between nonlinear continuous BMI and kidney function. RESULTS: We obtained data for 3,952 patients, with 350 (8.9%) in-hospital deaths. When compared with medium–high BMI, low BMI was associated with an increased risk of death and longer hospital stay, whereas the other two categories were comparable. Models using a cubic spline showing an association between BMI and in-hospital death showed an L-shaped curve; BMI < 22.0 kg/m(2) was associated with an increased risk for mortality, and at a BMI of 18.5 kg/m(2), the odds ratio was 1.43 with a 95% confidence interval of 1.26–1.61 when compared with a BMI of 22.0 kg/m(2). Analysis of the interactive effects of kidney function using the generalised additive model showed that a protective association of high BMI tapered along with decreased kidney function. CONCLUSIONS: This cohort study suggests not only that lower BMI and low kidney function are associated with in-hospital mortality independently but also that the protective effects of high BMI weaken as kidney function decreases via the analysis of the interaction terms. This study highlights the necessity for the prevention of underweight and demonstrates the interaction between BMI and kidney function in older patients with non-dialysis-dependent CKD. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12877-022-03659-3.