Obesity and risk of post-operative pneumonia among older adult patients with hip fracture: An obesity paradox

Background & aim: Hip fracture is a condition with a high incidence among older adults and is associated with a high post-operative mortality rate. Post-operative pneumonia is one of the most important risk factors for mortality, making its prevention essential. In recent years, reports on obesity paradoxes have increasingly been documented. Therefore, this study aimed to investigate the relationship between body mass index (BMI) and the risk of developing post-operative pneumonia using a large database. Method: We included 407,203 patients aged 75 years or older who underwent surgery for hip fracture between 2014 and 2018 using Diagnosis Procedure Combination data, a healthcare reimbursement system. Patients were classified into six BMI categories: <16.0, 16.0-16.9, 17.0-18.4, 18.5-24.9, 25.0-29.9, and >= 30 kg/m(2). Multilevel logistic regression analysis was performed based on BMI 18.5-24.9 kg/m(2) to determine odds ratios for post-operative pneumonia. Results: The data of 332,768 patients were included in the final analysis. Those with BMI <18.5 kg/m(2) demonstrated significantly higher odds of developing post-operative pneumonia compared to those with BMI between 18.5 and 24.9 kg/m(2), BMI <16.0 kg/m(2) (adjusted odds ratio [AOR: 2.14, 95 % confidence interval [CI: 2.01-2.27 p < 0.001); BMI 16.0-16.9 kg/m(2) (AOR: 1.57, 95 % CI: 1.46-1.69, p < 0.001); and BMI 17.0-18.4 kg/m(2) (AOR: 1.31, 95 % CI: 1.24-1.39, p < 0.001). Conversely, patients with BMI 25.0-29.9 kg/m(2) showed a reduced risk of post-operative pneumonia compared to the other groups (AOR: 0.83, 95 % CI: 0.76-0.91, p < 0.001). Notably, a J-curve relationship was observed between BMI and the incidence of post-operative pneumonia. Conclusion: Patients with higher BMI had a lower risk of developing post-operative pneumonia, revealing the presence of an obesity paradox between hip fracture and post-operative pneumonia. Patients with low BMI are at a higher risk and may benefit from enhanced preventive measures to mitigate the risk of pneumonia. (c) 2025 The Authors. Published by Elsevier Ltd on behalf of European Society for Clinical Nutrition and Metabolism. This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/).