That's because stress in appropriate amounts is the very stimulation that keeps us engaged with the world moment to moment.
When the brain perceives a stimulus, the sympathetic nervous system kicks into gear. It tells the adrenal glands to release the first stress hormone, epinephrine (aka adrenaline). Epinephrine dilates the bronchial tubes in the lungs to make space for more oxygen and charges the heart, enabling more blood to push through. It dilates the blood vessels leading away from the heart, too, so that oxygenated blood can flow freely to where it's needed most: the brain and the muscles, which must be ready to flee or fight.
Next, the hormone norepinephrine spurts from the nerve endings of the sympathetic nervous system. Norepinephrine constricts the veins leading to the heart so returning blood can slam more powerfully into the chamber and exit with even more force. It constricts the arteries leading to the skin, too, to slow down bleeding in the event of an injury.
Finally, the third—and major—stress hormone, cortisol, joins the party, also emanating from the adrenal glands, to mobilize cells' stored energy and to keep the rations coming for the duration of the stressor. In nonemergency situations, cortisol follows the body's circadian rhythms: It's highest in the early morning—time to wake up—and lowest at night.
"Our goal isn't a life without stress," Stanford University neurobiologist Robert M. Sapolsky says. "The idea is to have the right amount of stress." That means stressors that are short-lived and manageable.
You experience good stress when you feel a sense of control over the event in question. No matter how your body may respond in the moment, you know you're going to come out fine on the other side—and perhaps even better for the experience. A roller coaster ride may send your stress-hormone levels soaring, but you know the ride will be over in minutes. Sapolsky explains this as "voluntarily relinquishing a degree of control and predictability in a setting that is benevolent overall."
Duration is key, but so is your perception of the external event, says psychologist Wendy Berry Mendes, of the University of California, San Francisco. Do you frame the stressor as a challenge or a threat?
Imagine you're waiting in the wings before a presentation, flipping through your Powerpoint slides in your mind's eye. You know you can do this! Epinephrine shoots into your system; norepinephrine follows, but in lesser amounts. Your heart rate increases, your hands get warm, your eyes light up. Cortisol inches up. This is challenge stress. You're ready to fly.
"A challenge response [physiologically] looks a lot like aerobic activity," says Mendes. Sex is a form of challenge stress. And good things come from challenge stress, including the growth of new brains cells. Resistance exercise also qualifies as a challenge stress, when it's not overdone. Mark A. Tarnopolsky, a muscle metabolism and neuromuscular disease specialist at McMaster University Medical Centre, in Hamilton, Ontario, has found that pumping iron can shift the genetic profile of old muscles to that of younger ones.
But consider a scenario wherein you're so worried about the presentation you can't sleep the night before. The lack of sleep leaves your amygdala on high alert. Moments before the talk, you're still mentally flipping those Powerpoint slides, but you can't make out the images. Norepinephrine has beaten out epinephrine, causing more constriction than dilation of your blood vessels. Your heart rate increases, but less blood is pushed to the brain and body. Cortisol gushes. Your hands go cold and your mind goes blank. This is "threat" stress. Your presentation may be toast.
The story worsens if the threat continues—that is, if the stress becomes chronic. Then you experience what neuroendocrinologist Bruce McEwen of The Rockefeller University, in New York City, calls toxic stress—you're overwhelmed and feel out of control. "Things are coming at you left and right," he says. "You can't keep up with them. There is the danger of developing a sort of 'learned helplessness' "—that is, not even trying to cope anymore because you feel there is no point. "The more threatened you feel, the less capable you feel," says McEwen, "and the worse your physiology is going to be as a result."
A Tipping Point?
Is there an identifiable tipping point—a place where, through physiological cues, we know that we've slipped past good stress and into the danger zone? When it comes to the performance of specific tasks, there is.
In the first phase of the stress response, when just epinephrine and norepinephrine are flowing, performance improves continuously as levels of the two hormones
increase, whether the challenge is mental (you're taking a math test) or physical (you're parachuting out of a plane). But once cortisol joins the party, everything changes.
For years, stress researchers have noted a relationship between levels of cortisol and the ability to remember things, in particular, those with an emotional component. Increased levels of cortisol affect memory in a hill-shaped curve: Increased cortisol boosts the ability to remember—up to the top of the hill. But after that point, memory decreases as cortisol levels continue to climb. Too much of a good thing becomes a bad thing. If you're stressed and your memory starts to go, you know you've crossed the line.
That curve has a name: The Yerkes-Dodson law. It was established a century ago when the two eponymous psychologists traced how electric shocks to mice affected their ability to avoid a black box.
Why does Yerkes-Dodson swing into action when cortisol arrives? In the early stages of a stressor, cortisol attaches to receptors in the hippocampus that enhance memory formation; they're called mineralocorticoid receptors. But if the stressor continues, the memory-enhancing receptors fill up, and the cortisol attaches to a different type of receptor—one that disrupts memory; this is a glucocorticoid receptor.
Indeed, a long-term surplus of cortisol in the brain can cause dendrites in the hippocampus to wither. Think of a dendrite as an old-fashioned telephone line: It's a fiber-like projection at the end of a brain cell that receives electrical messages from other brain cells. Retract that line and you muck up the message.
What's a Stressed-Out Person To Do?
Given the physiological realities, the Holy Grail of stress management would be to identify the optimal amount of stress for every individual.
Yet there is no uniform right amount of stress. Each of us has a different stress threshold—that is, the degree of stress needed to benefit or harm us—depending on our history and even our genetic makeup. For sure, there are events that are universally rated high stress: you lose your job or a loved one, a tropical storm floods your basement, you are in the midst of a messy divorce. But what matters most regarding health and even longevity is not the event itself but how you respond to it. And how you respond—emotionally and physiologically—depends on how you perceive it.
Consider the flood scenario: You come home from an afternoon out amid torrents of rain. Water is rising in your basement as high as your desk top. Your husband is pacing and cursing, his blood pressure is through the roof. "We're in big trouble," he mutters. He can't think straight. His hands are clammy, his breath is shallow. He's headed toward hypertension, or worse.
You, on the other hand, feel your heart rate pick up. Your vision clears. You know what to do! You jump back in your car and race to Home Depot, where you grab the last portable pump from the shelf. Home again, you plug in the contraption, attaching a rubber hose that extends up the basement stairs and into the street. You feel a glow as water gushes out of the house.
Our perceptions spring from our disposition, which arises from our history and our genes. Whereas emotions and mood are fluid, dispositions are more fixed. Someone who's generally anxious is likely to see a stressor as a threat, while someone who's resilient will see that same stressor as a challenge. In the anxious person, the prefrontal cortex—the seat of executive function—may be less well-developed and thus have less control over the amygdala and its access to fear memories.
"People who are prone to anxiety disorders, post-traumatic stress disorder, or depression have imbalances in those circuits and their underlying chemistry," says McEwen. "And that makes them react to a situation in a more anxious way than another person. So, the idea of how much stress is too much is as much an internal or individual problem as anything else."
Yet, regardless of your upbringing or personality, there is good news: Science has shown that we can all alter our perceptions. We can, with training, transform a threat into a challenge. We can even stressproof our brain, raising our overall stress threshold. And when stressors subside, most of the damage—retracting dendrites, for example, or an overgrown amygdala—can be reversed. We can improve our overall health and add years to our lives.
A new study led by UC San Francisco's Mendes shows one way to do this: by reappraising our own physiological responses. How we interpret a racing heart and quickened breath can determine whether we'll experience good or bad stress.
Mendes and colleagues found that subjects who were prepped to interpret stress-related physiological responses as positive had increased cardiac efficiency and more blood-vessel dilation than those who were either prepped to ignore a stressor or not prepped at all. In other words, whether the subjects experienced challenge stress (warm hands, alert brain) or threat stress (cold hands, mind blank) depended on their appraisal of their own physical state.
"In both of those cases, you're experiencing increased arousal," Mendes says. "But there's a fork in the road: You can shift to a more positive response to the stressor. You activate which way you're going to go."
So the next time you are beside yourself about a big presentation—or any onerous task—consider how Mendes's subjects handled a speech delivered to two scowling evaluators. One group of subjects read articles about how physiological responses to stressors aid performance, another read articles about how ignoring stressors was most helpful (they were told to look away from the frowning evaluators), and the third didn't read any articles beforehand.
The benefits of the first group's reappraisal extended beyond their ability to wow an audience. Those prepped to interpret their racing hearts as positive adopted a glass-half-full frame of mind: In a test, they were less likely to latch onto negative words such as "failure" and "fear."
Mendes calls her paper, appropriately, "Mind Over Matter," and leads it off with a prescient quote from American psychologist and philosopher William James. "The greatest weapon against stress is our ability to choose one thought over another," James wrote.
Can you feel your blood pressure dropping already?
8 Steps to Stress-Proof Your Day
Reinterpret a negative experience Say you leave your headphones in the car when you go to the gym. Interpret the return trip to the car not as an irritant but as a chance to warm up before you even climb on the treadmill.
Give to someone else Doing something nice for others can make you happier and calmer, studies show.
Jot down attainable goals for the week and aim to achieve one every day. This is a great way to track what's going right.
Build social support Brain scans show that the same circuitry fires up when we feel emotional pain as when we feel physical pain. But that circuitry is slower to react in those with greater social support in their daily lives.
Notice at least one good thing you experience each day. Then make it "real" by telling someone about it or writing it down. The event can be as small as getting out of bed on time.
Meditate Meditation can actually alter our brains, increasing gray matter in regions associated with emotion regulation and dampening activity in the fear-responsive amygdala.
Get enough sleep Sleep deprivation is one of the greatest angst inducers—it causes stress hormones to soar and sparks other imbalances.
Exercise regularly Exercise works as a mild or "good" stressor: One hundred and fifty minutes of moderate intensity exercise a week is linked with both reduced stress levels and increased growth of new brain cells.
How Stressed Do You Feel?
The following questions pertain to your feelings and thoughts during the last month. In each case, circle how often you felt or thought a certain way.
0 = Never
1 = Almost Never
2 = Sometimes
3 = Fairly Often
4 = Very Often
1. In the last month, how often have you been upset because of something that happened unexpectedly?
0 1 2 3 4
2. In the last month, how often have you felt that you were unable to control the important things in your life?
0 1 2 3 4
3. In the last month, how often have you felt nervous and stressed?
0 1 2 3 4
4. In the last month, how often have you felt confident about your ability to handle your personal problems?
0 1 2 3 4
5. In the last month, how often have you felt that things were going your way?
0 1 2 3 4
6. In the last month, how often have you found that you could not cope with all the things that you had to do?
0 1 2 3 4
7. In the last month, how often have you been able to control irritations in your life?
0 1 2 3 4
8. In the last month, how often have you felt that you were on top of things?
0 1 2 3 4
9. In the last month, how often have you been angered because of things that were outside of your control?
0 1 2 3 4
10. In the last month, how often have you felt difficulties were piling up so high that you could not overcome them?
0 1 2 3 4
Calculating your score:
1. Take your responses to questions 4, 5, 7, and 8 and reverse each one. That is, if you circled 0, give the response the value of 4; if you circled 1, give the response the value of 3; and so on: 2 = 2, 3 = 1, 4 = 0. Add up the reversed values.
2. Add up your responses to the remaining questions: 1, 2, 3, 6, 9, 10. 3. Add the sums from (1) and (2) to get your total score.Scores range from 0-40. The higher your score, the more stressed-out you feel.
Interpreting your score: * 0-10 = low stress, 11-20 = medium stress, 21-30 = high stress, 31-40 = extreme stress