The science of stress
Stress starts in the brain. The Mayo Clinic refers to stress as a “complex natural alarm system.” At the base of the brain, there is a small part called the hypothalamus. When triggered by stress, the hypothalamus sets off a cascade of reactions through two different systems: your nervous system and your hormonal system. By understanding these mechanisms, it will become clear how your body physically and mentally reacts to stress with so many possible symptoms and why this increases your risks for many health conditions and diseases.
Stress makes your nervous system more alert and ready to fight, flee, or freeze. One way it does this is by redistributing your body’s resources away from non-essential functions by hyper activating the sympathetic part of your autonomic nervous system.[5,8] This means that it tells the nerves that control your attention, heart rate, blood pressure, breathing, and muscles to ramp up, while at the same time, telling the nerves that control your digestion, immune response, and reproduction that they’re not really needed as much in this stressful moment, so they can hang tight for a while.
When it comes to the hormonal response to stress, this happens via the hypothalamic-pituitary-adrenal axis (HPA-axis).[5,9,10] One of the major messages from your brain’s hypothalamus goes to your adrenal glands, located on top of your kidneys.[7,10] These glands produce the powerful stress hormones cortisol and adrenaline (also known as epinephrine). These two hormones direct your body to hold off on any resting, digesting, immunity, or reproduction because they’ve been told that your body’s focus and resources need to go toward survival.
These stress reactions happen because your brain and muscles are getting prepared for moving quickly and powerfully. Your heart rate, blood pressure, and breathing increase to supply your brain and muscles with more oxygen.[5,7] Your blood sugar level increases to supply them with fuel.
PRO TIP: Remember your stress reactions are biologically the same whether it’s to literally save your life or if your stress is due to a triggering, annoying, or frustrating situation. That’s not your fault. That’s biology.
When you’re stressed, you may have less control over food cravings. An interesting recent finding is that ghrelin—the “hunger” hormone—is also activated in response to stress. Studies show that, upon acute stress, high levels of ghrelin are immediately released by the stomach into the bloodstream to promote food-seeking and meal initiation. It’s possible that by releasing ghrelin when stressed, the eating that follows helps people alleviate some of their stress. When stress subsides, the levels of ghrelin decrease slowly over the course of minutes or hours, even if nothing is eaten.
Interestingly, the ghrelin response seems to be higher and last longer for people who have excess weight or obesity. Researchers believe that ghrelin’s role in promoting eating during stressful times may be one of the reasons why stress is linked to obesity and difficulty in losing weight. As of now, it is not known which comes first: a higher ghrelin response to stress which contributes to the development of obesity or whether people with obesity develop a heightened ghrelin response as a result of weight gain. More research will likely sort this out in the future.
As you can imagine, once the stressful situation has passed, all of these stress hormones slowly drop down to normal levels and your body can start going back to its normal state. Your heart rate, blood pressure, breathing, and blood sugar all reduce, and your body can start picking up where it left off in terms of resting, digestion, immunity, and reproduction.
The difference between acute (short-term) stress and chronic (long-term) stress is that with chronic stress, you constantly feel demands and threats over the long run, so this biological reaction continues. This is where long-term consequences such as increased risks for anxiety, depression, digestive issues, headaches, muscle tension, heart disease risk, sleep problems, and weight issues may come into play.
With all of these biological responses, our nervous system and hormones focus on ensuring your body’s resources are focused on survival in this immediate present danger, even if the stressor isn’t, in fact, immediately a matter of life or death. This explains how stress can have such a vast array of seemingly unrelated symptoms: digestive distress, headaches, muscle tension, susceptibility to infections, mood changes, etc., and how living in this stressful state too often for too long can lead to more serious issues mentioned above.
Summary about stress
Stress is a completely natural physical and mental reaction to life’s demands. Stress is not all bad—it can help you reach your goals or literally save your life. The problem is chronic stress because your body responds to all stress in the same way by instantly prioritizing survival mechanisms of fighting, fleeing, or freezing. This means it increases your alertness, blood pressure, blood sugar, and breathing. It also means that it de-prioritizes your ability to rest, digest, fight infections, and reproduce. When stress goes on for a long time and your body and mind don’t get a chance to normalize, that’s when it can have harmful effects on your mental and physical health.
Dealing with stress can be a challenge, but there are many things you can do to try to mitigate the stressor itself. And there are also effective ways to cope and manage your reaction to these stressors in a healthy way. In the next part, I will go over some of the common—and uncommon—strategies to help you better manage your stress and reduce those stressors in a healthy and productive way.
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