Annual new dementia cases worldwide may increase from approximately 11.4 million in 2023 to 24.7 million by 2050 as populations age. Researchers also found higher age-standardized dementia incidence among women than men and in low- and middle-income countries compared with high-income countries.
The meta-analysis included individual-participant data from 38,418 adults aged 60 years or older without dementia at baseline across 22 population-based longitudinal cohorts from the Cohort Studies of Memory in an International Consortium (COSMIC), spanning18 countries or territories on 6 continents. Baseline recruitment began between 1990 and 2011, with follow-up data extending through 2021. Researchers used a harmonized, 2-step meta-analysis incorporating Poisson regression models, inverse-probability censoring weights, and random effects to account for differences between studies and countries. During 287,632 person-years of follow-up, 3,001 participants developed dementia.
The primary outcome was the incidence of all-cause dementia, determined using clinically based diagnostic criteria and expressed as new cases per 1,000 person-years at risk. The researchers calculated age- and sex-standardized incidence rates using the 2023 global population structure. Secondary analyses examined differences by sex, country income level, and geographic region, alongside projections of new dementia cases through 2050.
The global age- and sex-standardized dementia incidence rate among adults aged 60 years or older was 9.7 per 1,000 person-years. Applying age- and sex-specific incidence rates to the projected 2050 population yielded an estimated 117%increase in annual new cases compared with 2023.
Age-standardized dementia incidence was statistically significantly higher among women than men, at 10.6 vs 8.6 cases per 1,000 person-years. However, crude incidence rates did not differ statistically significantly by sex. The pattern of higher age-standardized incidence among women was observed in both high-income and low- and middle-income countries.
Differences were also observed by country income level. Age- and sex-standardized incidence was 13.6 per 1,000 person-years in low- and middle-income countries compared with 8.3 in high-income countries. In exploratory analyses, lower educational attainment was more strongly associated with higher dementia incidence in low- and middle-income countries, although differences in how education was measured and the small number of contributing cohorts limited interpretation of the findings.
Across geographic regions, standardized incidence estimates ranged from 7.6 per 1,000 person-years in Oceania to 13.1 in Latin America. However, differences between regions were not statistically significant. The researchers emphasized that several regional estimates were based on relatively few cohorts and should not be interpreted as representative of entire continents or countries.
The study had several limitations. The projections assumed that age- and sex-specific incidence rates would remain constant over time. Consequently, the projected increase in new dementia cases reflected demographic aging rather than demonstrated changes in underlying dementia risk. Geographic representation was uneven, with limited data from Africa, Latin America, and Oceania and no cohorts from the Middle East. Substantial between-study heterogeneity, differences in diagnostic methods, and potentially unrepresentative national samples further limited generalizability.
The findings provide a benchmark for comparing dementia incidence across populations, although differences in cohort representation and diagnostic methods warrant caution when interpreting regional estimates. “The observed sex- and income-stratified differences, together with substantial cross-country variation, highlight the need for targeted equitable prevention strategies and expanded diagnostic and care capacity,” wrote lead study author Ashleigh S. Vella, PhD, of the Centre for Healthy Brain Ageing at the University of New South Wales, Sydney, Australia, and colleagues.
The study received funding from the National Institute on Aging and other sources supporting participating cohorts. Vella reportedsalary support through a National Institute on Aging grant. Several coauthors disclosed research grants, consulting or advisory fees, and other financial relationships involving Eisai, Eli Lilly, Novo Nordisk, and Roche.
Source: JAMA Neurology
