Abstract
This study investigates short-term fluctuations in body weight (BW) as potential early indicators of frailty and their association with subsequent adverse outcomes in an aging Japanese population. Using longitudinal data from Tama City’s national health insurance cohort, we examined adults aged 40 years and older who had BW measurements at baseline (2016) and a follow-up in 2017, with subsequent health, nursing-care, and mortality data through 2023. Participants were categorized into three BW-change groups between 2016 and 2017: weight loss of 5% or more (n = 1,080), weight change within ± 5% (13,661), and weight gain of 5% or more (959). Kaplan–Meier analyses demonstrated that BW change within one year was associated with higher incidences of dementia onset, hospitalization for congestive heart failure, need for long-term care, and all-cause mortality, with the pattern BW loss > BW gain > stable in event rates (p < 0.05). Multivariate Cox proportional hazards models identified BW loss as an independent predictor for multiple adverse outcomes, including bone fracture, dementia, need for long-term care, stroke, CHF, and all-cause mortality. BW gain also had a significantly higher incidence of need for care (Hazard Ratio 1.159) and mortality (1.491). Medications such as hypnotics, proton pump inhibitors, anticoagulants, and antihypertensives, and sodium-glucose cotransporter 2 inhibitors were significantly predicted specific conditions related to frailty and/or atherosclerotic conditions. The findings in our study suggest that both short-term BW reductions and increases can signal imminent frailty development in older adults, potentially mediated by malnutrition, sarcopenia, edema, or fluid overload. BW dynamics, together with routine biomarkers (creatinine, Hb, ALT, lipid profiles), appear valuable for risk stratification and timely intervention in community-dwelling older adults. Clinically, these results advocate for dynamic nutritional surveillance and integrated management strategies aimed at maintaining weight stability and addressing reversible contributors to BW fluctuations. Limitations include the observational design and the specific regional, publicly insured cohort, which may limit generalizability. The causal relationships between specific medications and conditions related to frailty remain unclear. Further studies across diverse populations are warranted to confirm causal links between BW dynamics, frailty trajectories, and related health outcomes.
Data availability
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available because they contain information that could compromise the privacy of research participants. The data that supports the findings of this study are available on request until March, 2026.
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Acknowledgements
We thank all of the participants covered by Tama City national health insurance who provided consent to use their data. We thank the members of the Tama City Medical Association for their cooperation. We thank Mr. Hirohito Watanabe and Ms. Ayaka Hiratsuka (Hankyu Hanshin Holdings, Inc., Group Business Development Div., Business Development Dept.) for performing the statistical analysis. We thank Benjamin Knight, MSc., from Edanz (https://jp.edanz.com/ac) for editing a draft of this manuscript.
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This work was supported by the Tama City Medical Association as one of its research projects.
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HF performed the data collection and analysis and wrote the paper. HF is responsible for the overall content as a guarantor. HF accepts full responsibility for the finished work and/or the conduct of the study, had access to the data, and controlled the decision to publish. HN, HS, and YT performed the data collection and participated in discussions. EK and TK designed the study and provided expert clinical knowledge during critical revision. All authors approved the final version of the submitted manuscript.
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Due to the retrospective nature of the study, Institutional Review Board of Tama Center Mirai Clinic (no. 2024014) waived the need of obtaining informed consent.
Tama City included information on the application form for the checkup explaining that participants’ anonymized data may be analyzed and published for public health research and that they have the right to opt out or refuse their consent. The same information was provided on the TAMA CITY Medical Association website. Our study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). We obtained Institutional Review Board approval from the Tama Center Mirai Clinic (no. 2024014).
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Fujii, H., Kodani, E., Kaneko, T. et al. One-year body weight loss and gain as independent predictors of frailty-related outcomes and mortality in an aging Japanese population. Sci Rep (2026). https://doi.org/10.1038/s41598-026-39383-w
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DOI: https://doi.org/10.1038/s41598-026-39383-w
