Epigenetic mechanisms are implicated in the processes through which social stressors erode health in humans and other animals. Here I review progress in elucidating the biological pathways underlying the social gradient in health, with particular emphasis on how behavioral stresses influence epigenomic variation linked to health. The evidence that epigenetic changes are involved in embedding of social status-linked chronic stress is reviewed in the context of current knowledge about behavior within animal dominance hierarchies and the impacts of social position on behaviors that affect health. The roles of epigenetic mechanisms in responses to trauma and the evidence for their involvement in intergenerational transmission of the biological impacts of traumatic stress are also considered. Taken together, the emerging insights have important implications for development of strategies to improve societal health and well-being.
Psychosocial stress involves neurophysiological changes resulting from the anticipation or perception of challenges to well-being that are located within the social environment. Recent research to understand the sources and impacts of psychosocial stress reveals that epigenetic mechanisms are an important interface through which the body interprets and responds to stressful experiences. Psychosocial stressors with epigenetic impacts are encountered in a variety of different circumstances and over a wide range of timescales, ranging from the early-life adversity caused by deficiencies of parental care during infancy and childhood, to the long-term, chronic stress of socio-economic deprivation and the intense traumas of warfare, famine and genocide. The adaptive physiological response to an acute and temporary exposure to a stressor is known as allostasis, which mitigates the impacts of the stressor and restores physiological equilibrium once the exposure to stressor has subsided . Effective allostasis can facilitate coping under stress and development of resilience . However, under circumstances of chronic stress or trauma, the ability of allostatic processes to mount effective responses can become weakened, leading to allostatic overload, which is accompanied by loss of resilience and increased risks of behavioral and physiological dysfunction. Some of the social behaviors that can engender chronic stress are evolutionarily conserved in vertebrates, as are key components of the neural circuits that perceive, process and respond to social stressors. Experimental studies in model organisms, together with human epidemiological studies, indicate that in some situations, the behavioral consequences of psychosocial stress can be transmitted to offspring that are themselves not exposed to the psychosocial stressor , which raises important questions about the biological basis for such intergenerational transmission, and the potential roles of epigenetic mechanisms in these processes. Here, I take an integrative, interdisciplinary approach to reviewing what is known about the roles of epigenetic processes in mediating the biological impacts of signals originating in the social environment. Current understanding of these processes is informed by research from a wide range of disciplines, encompassing behavioral ecology, endocrinology and molecular biology of social animals, as well as studies of human behavior, psychology, epigenetics, epidemiology and public health.
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