ABSTRACT Dementia is a major global health challenge, and Alzheimer’s disease (AD) comprises 70% of dementia cases. Because AD has no effective treatment options, the Lancet Commission recently emphasized the critical need for effective, life-course prevention of AD. Epigenetic age acceleration (EAA), or increased DNA methylation (DNAm)-based age relative to chronological age, was identified as a powerful biomarker of AD-related neurobiological substrates and cognitive function in older adults. Likewise, our preliminary data demonstrated associations between EAA and cognitive function in midlife, a critical epoch in brain health when subclinical pathology first emerges, and dementia prevention may be most effective. Works by us and others have also identified associations between cardiovascular disease (CVD) risk factors and EAA, suggesting that EAA could help to explain the intricate link between early life heart and midlife brain health. Despite these intriguing data, prospective associations between childhood CVD risk factors and EAA in adulthood remain unknown and temporal associations are not established. In addition, there is a paucity of research examining the relationships of EAA with midlife cognitive function decline and AD-related neurobiological substrates. We hypothesize that EAA is associated with cognitive decline and neurobiological substrates in midlife and mediates the associations of early life CVD risk factors with these midlife brain health endpoints. To test this hypothesis, we will leverage the rich resources of the Bogalusa Heart Study (BHS), including life-long measures of CVD risk factors, three repeated measures of genome-wide DNAm in adulthood, and two midlife measures of cognitive function over 11-years follow-up in the full cohort of 1,298 BHS participants (850 whites and 448 African Americans). Furthermore, midlife AD-related neurobiological substrates from 3T magnetic resonance imaging (MRI) and amyloid photon emission tomography (PET) scans are also available in a random subsample of 350 BHS participants. As part of the on-going visit cycle (2020-2024), we propose MRI in another random subsample of 350 BHS participants, amyloid PET scans in another random subsample of 50 participants, along with an additional genome-wide DNAm measure in the full BHS cohort. With these data, we will assess prospective and temporal associations of early life CVD risk factors with EAA (Aim 1); examine the associations of EAA with 11-year changes in cognitive function (Aim 2) and neurobiological substrates in midlife (Aim 3); and analyze the mediating effects of EAA on associations of childhood CVD risk factors with midlife brain health endpoints (Aim 4). The molecular characterization of midlife brain health may have broad implications, ranging from the improvement of risk stratification and sub-phenotyping efforts to the pinpointing of molecular targets for drug development. Identifying CVD risk factor precursors to EAA might sugges...