PROJECT SUMMARY / ABSTRACT Despite recent gains in overall life expectancy in the US, racial/ethnic health disparities in older adults (age ≥65) persist and are widening. This includes disparities in health status, chronic disease burden, disability, and life expectancy for Black and Hispanic older adults compared with whites. Our previous work has identified mid-life (age 50-64) as a critical period when health disparities for racial/ethnic minorities are set and may potentially be intervened upon. The Affordable Care Act coverage expansions of 2014 have shown promise for reducing disparities in access and health, but the impact on middle-aged and older adults has been largely understudied. The overarching goal of this proposal is to examine whether exposure to ACA coverage (Medicaid and Marketplace plans) and access to care for middle-aged adults (age 50-64) may affect downstream health disparities in older adults (age ≥65). We will use two modeling approaches in all aims: a) interrupted time series analysis to assess the impact of the entire ACA coverage expansion on racial/ethnic disparities before vs. after 2014; and b) difference-in-differences (DID) analysis and event study models comparing Medicaid expansion vs. non-expansion states estimated for each racial/ethnic group (Black, Hispanic, white) to assess the specific impact of Medicaid on disparities. In all analyses, we will also examine heterogeneity of treatment effects by individual-level intersecting identities (race, ethnicity, gender, socioeconomic status) and area-level structural racism. With this approach, we will achieve the following specific aims: 1) Assess how racial/ethnic disparities in middle-aged adults’ health insurance coverage has changed before vs. after the ACA coverage expansions, using the American Community Survey; 2) Estimate racial/ethnic disparities in middle-aged adults’ health care access and out-of-pocket costs before and after the ACA coverage expansions, using the Health and Retirement Study (HRS) and the Current Population Survey; and 3) Investigate racial/ethnic disparities in middle-aged and older adults’ health, and older adults’ health care utilization and costs before and after the ACA, using the HRS-linked Medicare data. The proposed work is significant because, in a time of economic distress and worsening health disparities, it will directly inform US health insurance policies to improve health equity for vulnerable populations. The methods are innovative in using the natural experiment of the ACA and an explicit focus on structural racism to understand whether the upstream policy intervention of the ACA that affected coverage of middle-aged adults may impact trajectories of health and health care disparities of middle-aged and older adults as they age.