One-year body weight loss and gain as independent predictors of frailty-related outcomes and mortality in an aging Japanese population.

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.