Social relationships and physiological determinants of longevity across the human life span
Significance Although much evidence has accrued in research over the past 20 years on the strong causal associations between social relationships and health and longevity, important gaps remain in our understanding of the mechanisms, timing, and duration of these associations. This study integrates social and biological disciplinary perspectives and research to examine how social relationships "get under the skin" to affect physiological well being as individuals age. By combining data from and harmonizing measurement across four large nationally representative, population based, contemporary surveys using an innovative longitudinal life course design, this study provides previously unidentified evidence on the biological and life course mechanisms linking social relationship patterns with health. As such, our findings advance explanations of the emergence and progression of diseases across the human life span. Two decades of research indicate causal associations between social relationships and mortality, but important questions remain as to how social relationships affect health, when effects emerge, and how long they last. Drawing on data from four nationally representative longitudinal samples of the US population, we implemented an innovative life course design to assess the prospective association of both structural and functional dimensions of social relationships (social integration, social support, and social strain) with objectively measured biomarkers of physical health (C reactive protein, systolic and diastolic blood pressure, waist circumference, and body mass index) within each life stage, including adolescence and young, middle, and late adulthood, and compare such associations across life stages. We found that a higher degree of social integration was associated with lower risk of physiological dysregulation in a dose response manner in both early and later life. Conversely, lack of social connections was associated with vastly elevated risk in specific life stages. For example, social isolation increased the risk of inflammation by the same magnitude as physical inactivity in adolescence, and the effect of social isolation on hypertension exceeded that of clinical risk factors such as diabetes in old age. Analyses of multiple dimensions of social relationships within multiple samples across the life course produced consistent and robust associations with health. Physiological impacts of structural and functional dimensions of social relationships emerge uniquely in adolescence and midlife and persist into old age.
Proceedings of the National Academy of Sciences