Epigenetics and the International Classification of Functioning, Disability and Health Model: Bridging Nature, Nurture, and Patient-Centered Population Health.

Epigenetic processes enable environmental inputs such as diet, exercise, and health behaviors to reversibly tag DNA with chemical "marks" that increase or decrease the expression of an individual's genetic template. Over time, epigenetic adaptations enable the effects of healthy or unhealthy stresses to become stably expressed in the tissue of an organism, with important consequences for health and disease. New research indicates that seemingly non-biological factors such as social stress, poverty, and childhood hardship initiate epigenetic adaptations in gene pathways that govern inflammation and immunity, two of the greatest contributors to chronic diseases such as diabetes and obesity. Epigenetic processes therefore provide a biological bridge between the genome-an individual's genetic inheritance-and the Social Determinants of Health-the conditions in which they are born, grow, live, work, and age. This Perspective paper argues that physical therapy clinicians, researchers, and educators can use the theoretical framework provided by the International Classification of Functioning, Disability, and Health (ICF model) to harmonize new discoveries from both public health research and medically focused genomic research. The ICF model likewise captures the essential role played by physical activity and exercise, which initiate powerful and widespread epigenetic adaptations that promote health and functioning. In this proposed framework, epigenetic processes transduce the effects of the social determinants of health and behaviors such as exercise into stable biological adaptations that affect an individual's daily activities and their participation in social roles. By harmonizing "nature" and "nurture," physical therapists can approach patient care with a more integrated perspective, capitalizing on novel discoveries in precision medicine, rehabilitation science, and in population-level research. As the experts in physical activity and exercise, physical therapists are ideally positioned to drive progress in the new era of patient-centered population health care.