PROJECT SUMMARY/ABSTRACT Significance. Circadian and sleep disruption, and sleep disorders such as sleep apnea, are highly prevalent and associated with a host of adverse health outcomes including cardiovascular mortality and morbidity. African-Americans are disproportionately affected by disrupted/misaligned circadian rhythms, disrupted sleep and sleep apnea; which may be important, unique contributors to adverse CMB health in African-Americans. Reducing the burden of adverse cardiometabolic health in African-Americans may involve targeting both circadian rhythms and sleep. However, limited research exists on circadian rhythms in the natural environment of AAs, and there are major gaps in knowledge about the determinants of circadian and sleep disruption within African-Americans. We hypothesize that multilevel socio-environmental factors are drivers of circadian misalignment (a mismatch between the internal circadian system and behavioral or environmental cycles), which contribute to irregular sleep, and in turn disrupts physiologic processes such as blood pressure and metabolism in a socioeconomically diverse cohort of AAs. It is plausible that the hypothesized association differs by SES and individual resilience; thus, we will consider resilience as a protective factor that may mitigate the adverse effects of the environment. Approach. Leveraging resources from a well characterized cohort of African-Americans in Atlanta Georgia, we propose to use a repeated measures design to test the cumulative effects of real-time household- and neighborhood-level factors (e.g., socioeconomic status, light at night, noise, air pollution) on psychosocial factors, rigorously assessed circadian disruption/misalignment (including home dim light melatonin onset to measure internal endogenous biologic rhythms), sleep regularity (14-day actigraphy, diary) and apnea (in-home polysomnography) and relatedly, the impact of these measures on markers of CMB health in 400 AAs. To assess cardiometabolic health we will measure 24-hour blood pressure, arterial stiffness, and biochemical markers of inflammation and metabolic dysfunction. We will explore individual-level SES and resilience as effect modifiers of the hypothesized associations. Impact. The overarching aim of this R01 is to elucidate the largely unexplained high burden of adverse cardiometabolic health in African-Americans by specifically focusing on identifying the multilevel socio- environmental determinants of circadian and sleep disruption, and determining the relative impact of circadian and sleep disruption on markers of CMB health. This project will have a high impact, because it will identify salient socio-environmental factors (risk and protective) that contribute to circadian and sleep health in AAs, to inform culturally tailored multilevel interventions to reduce sleep and cardiovascular disparities.