The problem with modern stress is, it never seems to stop. "What happens within the body and in the brain where there's repeated exposure to uncontrollable stress is that the systems themselves begin to change. They have to adapt, so they don't return to the normal state," according to Dr. Steve Schleifer, chairman of psychiatry at the New Jersey School of Medicine. "This is when the brain certainly begins to get into trouble. This is when it's believed we're more likely to develop abnormalities in emotional and brain function that are associated with problems like chronic depression."

Stress and depression have much in common, so it's no surprise that one could lead to the other. In 1988, early stress researchers at Duke University attempted to trace the connection by injecting rats with corticotrophin releasing factor (CRF), a chemical that triggers the release of adrenaline and other brain chemicals in times of stress. They observed that CRF "produces a number of behavioral and physiological effects that are reminiscent of both an organism's response to stress and to the symptoms of patients with major depression. These include diminished food consumption, decreased sexual behavior, disturbed sleep, alterations in locomotor activity and sympathetic nervous system activation."

Being at red alert all day, every day, disrupts more than just the nervous system. Immunity is one of those expensive processes from which the body borrows in order to divert resources to more immediate needs. "We don't need the immune system to be working over-actively in a fight-or-flight condition," Dr. Schleifer explains. As a result, he warns, in cases of ongoing stress, "The failure of the immune system could make one susceptible either to minor infections, major infections, and possibly the development of cancer."

Even the heart gets short-changed by stress over the long term. According to Dr. Schleifer, "The blood will be more likely to clot in a condition of stress, and we know that's not good for you. It's something that can lead to heart disease." Epidemiologist Dr. Sylvia Smoller adds, "Certainly stress can have an effect on high blood pressure, which is a major risk factor for stroke and heart disease. And many studies have shown that, for example, depression and changes in depression are predictors of future heart disease."