Synergistic effects of underweight and dementia on in-hospital mortality during acute myocardial infarction

Abstract Aims Although the impact of underweight and dementia on mortality is clear, no large study has examined the synergistic impact of underweight and dementia on acute myocardial infarction (AMI) in real-world settings. Therefore, this study aimed to investigate the synergistic effects of underweight and dementia on in-hospital mortality in AMI patients using a nationwide administrative database. Methods and results This nationwide retrospective cohort study was performed using the Japanese nationwide administrative data (JROAD-DPC) of 474,979 AMI patients between April 2012 and March 2021. Of these patients, 424,500 with AMI were divided into four groups according to body mass index (18.5 kg/m² or ≥18.5 kg/m²) and dementia status (presence or absence). We investigated the association of underweight and dementia with in-hospital mortality. In-hospital mortality was highest in the underweight/dementia group (17.5%), followed by the non-underweight/dementia group (13.2%), the underweight/non-dementia group (11.6%), and lowest in the non-underweight/non-dementia group (5.0%). Multilevel mixed-effects logistic regression analysis with multiple imputation and complete cases showed underweight and dementia to be associated alone and in combination with an increased risk of in-hospital mortality. In the subgroup analysis of age categories (75 vs ≥75 years), the synergistic effects of underweight and dementia on in-hospital mortality for AMI were greater for those 75 years of age. Conclusion This nationwide study suggested that the coexistence of underweight and dementia significantly increases the risk of in-hospital mortality in AMI patients and especially younger patients. Early detection and management of both conditions may be crucial for improving survival in this population.