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You are probably familiar with the signs of an adrenaline surge (racing pulse, hairs on the neck standing on end), which evolved to help us fight or flee predators and other immediate dangers. And you may have heard of cortisol, another stress hormone, which is produced more slowly than adrenaline and lingers in the bloodstream longer. But did you know that too little cortisol in your bloodstream can be just as bad as too much? Or that tucking into comfort foods, while soothing in the short term, can sabotage your long-term stress response by increasing the number of inflammatory proteins in your body?
What's emerging is a complex picture of the body's response to stress that involves several interrelated pathways. Scientists know the most about cortisol because until now that has been the easiest part to measure. "But when one thing changes, all the others change to some degree," says Bruce McEwen, a neuroendocrinologist at Rockefeller University who has spent decades studying the biology of stress, primarily in animals. So just because you see an imbalance in one area doesn't mean you understand why it is happening. "We're learning that post-traumatic stress disorder (PTSD), burnout, chronic fatigue syndrome and fibromyalgia are all related in some ways," McEwen says. The next step is to figure out if there are any genetic predispositions that tip the response to stress toward one set of symptoms or another.
YOU CAN'T AVOID STRESS
EVEN GETTING OUT OF BED CAN BE TOUGH ON THE BODY. SEVERAL hours before you wake each morning, a tiny region at the base of your cerebrum called the hypothalamus sends a signal that ultimately alerts your adrenal glands, which sit on top of your kidneys, to start pumping out cortisol, which acts as a wake-up signal. Cortisol levels continue to rise after you become conscious in what is sometimes referred to as the "Oh, s___! It's another day" response. This may help explain why so many heart attacks and strokes occur between 6 a.m. and 8 a.m.
Because cortisol is a long-acting hormone, you can dally under the covers a bit without losing any steam. But your brain is already taking steps to protect you from the shock of starting a new day. Rising cortisol levels signal the hypothalamus to stop sounding the alarm. Other parts of the brain chime in, and eventually the adrenal glands ratchet down their cortisol production. In other words, the brain's stress response contains its own off switch.
Most people's cortisol, as measured by a saliva test, peaks a few hours after waking. Levels then gradually decline during the course of the day--with a few blips scattered here and there. That pattern typically changes, however, in people who are severely depressed. Their cortisol level still rises early in the morning, but it stays high all day long. It's almost as if their hypothalamus has forgotten how to turn off the stress response. (Intriguingly, people who are sleep deprived also exhibit a high, flat cortisol level.)