Stress and Disease

"Exposure to chronic stress markedly increases vulnerability to adverse medical outcomes. This holds true across a wide variety of mental and physical conditions.  For example, persons facing chronic stress are more likely to develop an episode of clinical depression, experience symptoms of an upper respiratory infection following viral exposure, suffer from a flare up of an existing allergic or autoimmune condition, and show accelerated progression of chronic diseases such as acquired immunodeficiency syndrome and coronary heart disease...This phenomenon is apparent across the entire lifespan. From early in childhood to late in adulthood, chronic stress is accompanied by worse health and the magnitude of this effect is substantial: In some cases, exposure to chronic stress triples or quadruples the chances of an adverse medical outcome."

Miller, G.E.,  Chen, E. & Zhou, E.S. (2007).  If It Goes Up, Must It Come Down? Chronic Stress and the Hypothalamic-Pituitary-Adrenocortical Axis in Humans.  Psychological Bulletin, 133 (1), 25–45.