Alzheimer's disease and related dementias in South and Southeast Asia: a systematic review and meta-analysis of epidemiology and associated factors.

OBJECTIVES: Alzheimer's disease and related dementias (AD/ADRDs) are rising global public health challenges, disproportionately affecting ageing populations. Although higher prevalence estimates have been reported in high-income countries (HICs), the most rapid increase in dementia burden is projected to occur in low- and middle-income countries (LMICs), particularly in South and Southeast Asia. Genetic predisposition and non-modifiable risk factors interplay with vascular, lifestyle and environmental factors, shaping future disease burden. However, evidence from South and Southeast Asia remains fragmented, limiting targeted policy responses. This review systematically synthesises available evidence on prevalence and associated factors to inform prevention and care strategies. DESIGN: Systematic review and meta-analysis of AD/ADRDs prevalence and associated factors related studies from South and Southeast Asia. DATA SOURCES: Five electronic databases including PubMed, Scopus, CINAHL, EMBASE, APA PsycNet and hand searching of reference lists up to 1 May 2025. ELIGIBILITY CRITERIA FOR SELECTING STUDIES: The designed study included observational studies, specifically cross-sectional, casecontrol and cohort designs that reported the epidemiological characteristics and associated factors of AD/ADRDs. DATA EXTRACTION AND SYNTHESIS: Study screening, data extraction and methodological assessments were conducted by two independent reviewers. Risk of bias was assessed using the modified Newcastle-Ottawa Scale (mNOS). A restricted maximum likelihood model was used to synthesise results, complemented by synthesis of associated risk factors. Between-study heterogeneity was assessed using I² statistic. RESULTS: A total of 31 studies were included, of which 13 were analysed to estimate pooled prevalence (N=56 340). The methodological quality was good (mean mNOS=7.1, SD 0.99). The pooled age of onset of AD was 70.7 (SD 5.5) years, with one-third (46.3%) of the men surviving for 5 years. The overall estimated prevalence of dementia was 3.0% (95% CI 2.0% to 5.0%, I 2=98.7%), AD 2.0% (95% CI 1.0% to 4.0%, I 2=99.0%) and vascular dementia 1.0% (95% CI 0% to 1.0%, I 2=93.7%). Subgroup analysis showed that AD prevalence was 3.0% in LMICs (95% CI 1.0% to 6.0%) compared with 2.0% in HICs (95% CI 1.0% to 4.0%), and increased to 8.0% after 2010 (95% CI 5.0% to 14.0%) compared with 1.0% before 2000 (95% CI 0% to 2.0%). Additionally, results suggested that older adults had higher odds of AD (OR: 3.98, 95% CI 1.77% to 8.99%), while higher literacy, adequate sleep, periodontal therapy and cognitive stimulation were identified as protective factors. No clear evidence of an association between female gender, family history and AD risk was observed in the pooled analysis. CONCLUSIONS: AD affects a substantial and growing proportion of populations in South and Southeast Asia, with marked heterogeneity across settings. Evidence of an upward trend over the time in LMICs poses significant challenges in the coming years. The rising prevalence, associated factors particularly in resource-limited contexts, underscores the need for early-screening in clinical practices and region-specific epidemiological research. PROSPERO REGISTRATION NUMBER: CRD 420251047105.