Biological memories of past environments: Epigenetic pathways to health disparities

Human health tends to mirror gradients in social standing related to class, ethnicity and race. Past research in the social sciences suggests that environmental experiences related to social status contribute to these disparities, but the underlying biological mechanisms are only partially understood. Here, we review research related to three domains of environmental exposure that point to epigenetic contributions to health disparities: nutrition, psychosocial stress, and environmental toxicant exposure. Each exposure has effects that may persist across the life course and in some instances may be transmitted to offspring via epigenetic inheritance. Since epigenetic markings provide a "memory" of past experiences, minimizing future disparities in health will be partially contingent upon our ability to address inequality in the current environment. We suggest that future research in environmental epigenetics focus on establishing the reversibility of stress-induced epigenetic modifications, and also on identifying positive epigenetic effects of environmental enrichment.