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

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PROJECT SUMMARY By 2050, 75% of Alzheimer’s disease and related dementias (ADRD) cases will occur in low- and middle-income regions, like rural South Africa, which are severely under-represented in ADRD research. There is a critical evidence gap on the role of socioeconomic status (SES) in ADRD etiology in low-income settings, and how SES can best be targeted by interventions to prevent and/or delay ADRD onset. Our long-term goal is to inform the design of gender-equitable SES interventions to prevent and/or delay ADRD onset in low-income settings. The objective of this proposal is to identify how SES affects ADRD risk, using longitudinal exposures (household assets, food security, and employment) and randomized and quasi-randomized cash transfer exposures accumulated over time in mid-to-later-life in rural South Africa. Our central hypothesis is that greater cumulative exposure to advantageous socioeconomic conditions will protect against ADRD, with differential effects for men and women for household-level SES resources that may not be equally allocated between genders. To test this central hypothesis, we will leverage a unique opportunity to create one of the first longitudinal data platforms to study ADRD risk in Africa: we will link high-quality memory and ADRD outcome data collected from 2015-21 in the population-representative “Health and Aging in Africa: A Longitudinal Study of an INDEPTH Community in South Africa” (HAALSI; N=5059) to detailed SES exposure data collected since 2000 in the “Agincourt Health and Sociodemographic Surveillance System” (AHDSS; a census with 100% population coverage) and the HPTN 068 randomized controlled trial of cash transfers to households from 2011-15 (N=863 households in both HPTN 068 and HAALSI). These three datasets can be linked because the AHDSS census is the sampling frame for HAALSI and HPTN 068; we have confirmed linkage feasibility in our preliminary data. Specifically, we aim to: 1) Determine the roles of mid-to-later life cumulative household assets, employment, and food security (2000-13; AHDSS) in memory decline and ADRD risk (2015-21; HAALSI); 2) Determine whether exposure to cash transfer interventions affect memory decline and ADRD by leveraging 2a) randomized cash transfers in HPTN 068; 2b) expansion of the South African Old Age Pension for men; 2c) expansion of the South African Child Support Grant for mothers; and 3) Determine how gender modifies the effects of household-level SES exposures in Aims 1 & 2a. This proposal is innovative because the study population of older, rural Black South African adults improves representation of understudied groups in ADRD research; our longitudinal assessments of SES exposures over 14 years improve upon the status quo of SES measured retrospectively or at single points in time; and our linkage of the HAALSI cohort to a randomized controlled cash transfer trial and data on national social protection policies allows causal inference about income and ADRD risk. This proposal is a major opportunity for life course research in a rapidly aging, low-income population that can provide insights into ADRD etiology and strategies to prevent and/or delay ADRD onset in global low-income settings, where there is little data outside this study.