Probing effect modification by socioeconomic status in associations between blood biomarkers of neuropathology and cognitive outcomes in the United States and India.

INTRODUCTION: Socioeconomic factors influence cognitive outcomes and may modify associations between neuropathologies and cognitive outcomes, yet evidence from low- and middle-income contexts remains scarce. METHODS: We used harmonized data from nationally representative studies in the United States (Health and Retirement Study - Harmonized Cognitive Assessment Protocol [HRS-HCAP]; N = 1956) and India (Longitudinal Aging Study in India - Diagnostic Assessment of Dementia [LASI-DAD]; N = 1485) and multivariable-adjusted linear regression models to examine effect modification of associations between blood biomarkers of neuropathology (amyloid beta [Aβ]42/40, phosphorylated tau [p-tau-181], glial fibrillary acidic protein [GFAP], and neurofilament light chain [NfL]) and dementia-related outcomes (cognitive functioning, dementia) by socioeconomic factors (educational attainment, paternal education, and total household wealth and assets). RESULTS: Neuropathology biomarkers were associated with cognitive outcomes in both samples; however, no consistent evidence of effect modification by socioeconomic factors was observed across included biomarkers or cognitive measures. DISCUSSION: These findings suggested limited modification of blood biomarker-cognition relationships by socioeconomic status in diverse settings, potentially influenced by random measurement error, regression dilution bias, and low power. Further comparisons across biomarker modalities are warranted to clarify expected associations.