Project Summary/Abstract Functional impairment is increasingly prevalent among middle-aged and older adults, with 2 in 5 adults over the age of 65 having some form of disability, the majority being limitations on mobility. Many older adults are able to maintain functional capacity well into later life, but the factors that contribute to high levels of function and the mechanisms by which they operate are unclear. This proposal builds on prior work showing the importance of social relationships for health by investigating the role of social connectedness across the life course as a predictor of functional capacity in adulthood. This investigation will include not only marital but also family and friend relationships in adulthood, as well as parental affection and discipline in childhood to capture the life-course timing of specific types of relationships. The proposed study will use existing longitudinal data from the nationally representative Midlife in the United States (MIDUS) study to pursue three central aims. First, greater social connectedness across the life course is hypothesized to predict better functional capacity in adulthood and later life by way of greater physical activity and/or lower circulating levels of inflammatory biomarkers. Second, the research will identify potential divergent associations between life-course connectedness and health at different levels of socioeconomic status (SES). Finally, twin data in MIDUS will be used in within-family analyses to sharpen the focus on potential causal associations between life-course social connectedness and adult functional status. Results will demonstrate whether, when, and how life-course social connectedness predicts functional capacity, identifying potential mechanisms through which life-course social connectedness may influence health and strengthening or weakening the case for potential causal associations. In this way, findings will generate theory- and intervention- relevant insights into the successful maintenance of health, independence, and function across the lifespan. My long-term goal is to develop a research career focused on health, aging, and the life course, applying rigorous designs and analytical methods to better understand predictors of adult health. To better prepare myself for my career as an independent researcher, I am seeking training to: 1) cultivate a strong conceptual and methodological understanding of the life course perspective; 2) better understand how diverse social relationships across the life course shape adult health and health behavior; 3) leverage rigorous designs to examine predictors of adult health; and 4) build and sustain a career in interdisciplinary research. Training in these areas and research ethics is integral to completing the research aims and preparing me to launch a career-long, NIH-funded research program investigating biopsychosocial predictors of adult health.