How stress harms your physical and psychological health, from the Harvard Mental Health Letter

The car next to you suddenly veers over to your lane. You hit the brakes and it sails ahead. No harm done — except your muscles tense, your heart is pounding, and you are breathing faster. A cascade of stress hormones has produced a well orchestrated set of physiological changes sometimes called the "fight or flight response." Over the years, researchers have learned how and why these reactions occur, and have gained insight into the long-term effects stress has on physical and psychological health, reports the March 2011 issue of the Harvard Mental Health Letter.

The fight or flight response began as a survival mechanism that helped humans (and other mammals) react quickly to life-threatening situations. In the modern world, repeated activation of the stress response takes a toll on the body, contributing to high blood pressure, the development of artery-clogging plaque, and brain changes that may contribute to anxiety, depression, and addiction.