Cumulative socioeconomic exposures, cash transfer interventions, and later-life cognitive decline and dementia risk in a low-income region of South Africa

PROJECT SUMMARY By 2050, over 75% of Alzheimer’s disease and related dementia (ADRD) cases are projected to occur in low- and middle-income countries, such as South Africa. Government cash transfer programs as a form of social protection may increase individual and household income, with implications for ADRD risk. In the original project period of R01AG069128, we linked data from a cohort study of aging (HAALSI) and a randomized cash transfer trial (HPTN 068) to their shared sampling frame, a longitudinal regional census (AHDSS) in rural South Africa. We identified a protective causal effect of a randomized controlled cash transfer on later-life memory decline, dementia probability, and mortality risk, and causal relationships between expansions of two South African government cash transfer programs and the later-life cognitive health of their targeted recipients. Now, there is a critical need to determine how to optimize cash transfer program design to most effectively leverage cash transfer income to protect against ADRD. South Africa is an ideal setting for this research given its robust and expanding government portfolio of cash transfer programs. Our overarching goal for the proposed renewal of R01AG069128 is to expand our successful data linkage platform to identify the optimal amounts, durations, target recipients, and adult life course periods whereby cash transfer income may protect against later-life ADRD. Our central hypothesis is that greater accumulation of individual-level and household-level cash transfers across the adult life course will result in slower memory decline, lower incidence of ADRD, and greater cognitive reserve, and will also lead to investments in cognitively stimulating household resources. To test this hypothesis, we will newly map historical eligibility for multiple sources of cash transfer income for all HAALSI participants and their household members over a 23-year exposure period (1993-2014/15) and link these eligibility histories to new follow-up data on memory decline and ADRD in HAALSI over 13 years (2014/15-2027). In addition, we will add cognitive reserve as a new study outcome, operationalized from neuroimaging and neuropsychological data in the HAALSI Dementia Study (n=700; 2024/25). We aim to 1) determine the role of access to cash transfers accumulated across the adult life course at the individual- and household-levels in slowing later-life memory decline, reducing ADRD risk, and promoting cognitive reserve; 2) determine the relative importance of adult life course timing and trajectories of household access to cash transfers for memory decline, ADRD risk, and cognitive reserve; and, 3) compare later-life asset ownership and expenditures on cognitively stimulating resources across households according to their accumulated access to cash transfers. Over 130 countries use cash transfers as a form of social protection, including the United States, and more are considering or piloting cash transfer programs. The ADRD impacts of these programs are unknown, and actionable evidence is needed for them to optimally support the health and longevity of the rapidly aging populations that they serve.