Zhuoshen Lin, Wenjing Liao, Meiqian Xu, Tianlong Li, Lijuan Song, Gui Chen, Huakang Du, Guofei Feng, Zhiming Feng, Qi Zhang, Yabang Chen, Jiayi Liu, Baoxin Peng, Jianlei Xie, Xiaowen Zhang
Background: Olfactory dysfunction is a highly prevalent sensory deficit in older adults and a recognised early indicator of biological ageing and neurodegenerative disorders. Emerging epidemiological evidence links olfactory impairment to an elevated risk of all-cause mortality, yet methodological variations in how olfactory dysfunction is defined and assessed across studies have led to inconsistent effect estimates, necessitating a systematic, quantitative synthesis of the evidence. Methods: Following the PRISMA guidelines, we systematically searched PubMed and the Cochrane Library for cohort studies published up to 1 July 2025 that investigated the association between olfactory dysfunction and mortality in older adults. We used a multilevel meta-analytic model with restricted maximum likelihood estimation to calculate pooled hazard ratios (HRs) and 95% confidence intervals (CIs). Results: We identified 14 eligible cohort studies (12 included in meta-analysis). Olfactory dysfunction was associated with an increased risk of all-cause mortality, with a pooled HR of 1.20 (95% CI = 1.11, 1.29, P < 0.001). Publication bias was detected (Egger's test, P = 0.0003), and Trim-and-Fill correction attenuated the pooled HR to 1.09 (95% CI = 1.00, 1.19), with the association remaining statistically significant. Sensitivity analyses confirmed the robustness of the primary finding, with no single study driving the association. Conclusions: Olfactory dysfunction is associated with all-cause mortality risk in older adults, with the strength of this association strongly influenced by methodological choices in the definition and assessment of olfactory function. These findings highlight olfactory dysfunction as a potential surrogate marker of systemic physiological decline in ageing populations and underscore the critical need for standardised olfactory assessment methodologies in future epidemiological and geriatric research to improve the comparability and clinical translation of evidence. Registration: PROSPERO: CRD420251173699.