Global, regional, and national burden of age-related hearing loss and Alzheimer's disease, 1990-2021, with projections to 2040: A global burden of disease study

BACKGROUND: Age-related hearing loss (ARHL) and Alzheimer's disease (AD) are major contributors to disability in older adults, yet their long-term epidemiological trajectories have rarely been examined together. Evidence linking sensory decline with cognitive deterioration is growing, but global patterns, socioeconomic gradients, and future projections remain unclear. METHODS: Using data from the GBD 2021 study, we assessed global, regional, and national burdens of ARHL and AD from 1990 to 2021 and projected trends to 2040. We analyzed prevalence, incidence, mortality, and disability-adjusted life-years (DALYs), and evaluated age- and sex-specific patterns. Associations with the Socio-demographic Index (SDI) and cross-country performance were examined using frontier analysis. The epidemiological co-distribution of ARHL and AD was further explored using descriptive, country-level correlation analyses. RESULTS: The two conditions showed distinct but converging trajectories. ARHL burden remained relatively stable globally, whereas AD incidence and DALYs increased steadily, especially among women and in older age groups. Projections indicate further growth of both conditions by 2040, with AD rising more sharply. SDI displayed a non-linear association with disease burden: higher SDI corresponded to greater reported incidence, yet frontier analysis revealed diminishing returns and wide performance gaps. A positive cross-national association between ARHL prevalence and AD DALYs was observed, reflecting shared age structures, demographic pressures, and reporting contexts across populations. CONCLUSION: This study provides an integrated, population-level description of the long-term and projected burdens of ARHL and AD using a unified analytical framework. The observed co-distribution of sensory and cognitive impairment highlights the importance of coordinated public health planning for aging populations, particularly in regions undergoing rapid demographic transition.