Household fuel type, kitchen ventilation, and frailty trajectory membership among older adults: a community-based longitudinal study in Nanjing, China

Background Longitudinal evidence jointly considering household fuel type and kitchen ventilation in relation to frailty trajectory membership among older adults remains limited. This study aimed to identify frailty index (FI) trajectories among community-dwelling older adults and examine their associations with household fuel type and kitchen ventilation. Methods We analysed annual health examination data from 2020 to 2023 for 47,947 community-dwelling adults aged 65 years or older in Nanjing, China, with at least three valid FI assessments. Frailty was measured using a 34-item FI. Latent class mixed models identified FI trajectories. Multivariable multinomial logistic regression examined the associations of baseline household fuel type and kitchen ventilation with trajectory membership. Results Three trajectories were identified: low-level progressive (26.47%), moderate-level gradual-increase (51.33%) and high-level persistent-burden (22.20%). They differed mainly in sustained FI levels, with modest increases over follow-up. With the low FI trajectory as the reference, solid fuel use versus clean fuel use among participants with ventilation was associated with membership in the moderate and high FI trajectories, with adjusted relative risk ratios (RRRs) of 1.496 (95% confidence interval [CI] 1.400–1.598) and 2.230 (95% CI 2.061–2.414), respectively. Among clean fuel users, the corresponding RRRs for absence versus presence of ventilation were 1.252 (95% CI 1.165–1.346) and 1.614 (95% CI 1.479–1.761). Analyses of follow-up FI adjusted for baseline FI supported these associations. Conclusions Solid fuel use among participants with kitchen ventilation and absence of ventilation among clean fuel users were associated with membership in higher-FI trajectories. These findings support considering both fuel type and ventilation when assessing household environments in older populations. Clinical trial number Not applicable.