Global incidence trends and projections of Alzheimer disease and other dementias: an age-period-cohort analysis 2021.

Background: Alzheimer disease (AD) is a growing global health issue, with incidence varying by gender, age, and region. Understanding these trends is essential for developing effective prevention strategies as the population ages. Unlike previous Global Burden of Disease (GBD) studies that primarily focussed on prevalence and mortality, we offer a novel perspective by examining historical incidence trends and projecting future patterns of AD and other dementias using advanced analytical approaches. Methods: We used data from 204 countries and 21 global regions from the GBD 2021 database. We applied the age-period-cohort (APC) model to analyse historical incidence trends, and the Bayesian APC (BAPC) model to forecast future incidence from 2022-36. These models help reveal changes related to age, period, and birth cohort and enable forecasting of future trends - analytical perspectives not provided in the original GBD data sets or their supplementary documents. Results: Between 1992-2021, global AD cases increased from 4.078 million to 9.837 million, while the global age-standardised incidence rate (ASIR) remained relatively stable, rising slightly from 117.7 to 119.8 per 100 000. ASIR increased significantly in high-middle and middle-sociodemographic index regions, but declined in the low-sociodemographic index regions. Women consistently exhibited higher incidence rates than men across all regions. Projections indicate that 2036 global AD cases will reach 19.117 million, with an ASIR of 418.92 per 100 000. Conclusions: While global ASIR has remained stable, the number of AD cases continues to rise due to population ageing, particularly in middle- and high-income regions. Low-income regions face additional challenges due to limited health care resources. Gender disparities and unequal access to health care contribute to the variations in disease burden. These findings emphasise the need to prioritise early diagnosis and implement targeted interventions to reduce future disease burdens and address global health care inequalities.