The Neuroscience Behind Why We Feel Stressed – and What to Do About It

“The same stress hormones that are essential for survival can have damaging effects on both physical and mental health if they are secreted over a longer period of time.”

GaudiLab / Shutterstock
GaudiLab / Shutterstock

Stress is also an emotion, one that we share with other animals and with one another across the life span, although the causes of stress can be quite variable. Chronic stress is especially harmful. Stress is also highly variable—what would stress out one person another takes in stride, and vice versa.

Stress can have a substantial impact on longevity. Consider an experiment with Pacific salmon. After swimming upstream to spawn, and releasing tons of glucocorticoids because of the stress, they die. It’s not because they’re exhausted, or for some other biologically preprogrammed reason— rather, they experience rapid aging because of the production of those stress hormones. When researchers removed the adrenal glands of the salmon, which release all those glucocorticoids, the salmon didn’t die after spawning.

As biologist Robert Sapolsky says,

“If you catch salmon right after they spawn . . . you find they have huge adrenal glands, peptic ulcers, and kidney lesions, their immune systems have collapsed . . . [and they] have stupendously high glucocorticoid concentrations in their bloodstreams.

The bizarre thing is that this sequence . . . not only occurs in five species of salmon, but also among a dozen species of Australian marsupial mice Pacific salmon and marsupial mice are not close relatives. At least twice in evolutionary history, completely independently, two very different sets of species have come up with the identical trick: If you want to degenerate very fast, secrete a ton of glucocorticoids.”

My University of Montreal colleague Sonia Lupien is one of the world experts on the physiology of stress. She writes:

“A week seldom passes without hearing or reading about stress and its deleterious effects on health. There is a great paradox in the field of stress research, and it relates to the fact that the popular definition of stress is very different from the scientific definition of stress.

In popular terms, stress is mainly defined as time pressure. We feel stressed when we do not have the time to perform the tasks we want to perform. In scientific terms, stress is not equivalent to time pressure. If this were true, every individual would feel stressed when pressured by time. However, we all know people who are extremely stressed by time pressure and others who actually seek time pressure to perform adequately (so-called procrastinators). This shows that stress is a highly individual experience.”

The term stress dates back to Old English in 1303 as a variant of distress and was typically used in contexts of coercion or bribery. In modern times, stress was first used by engineers in the 1850s to describe outside forces that could put a strain on a structure—heat, cold, and pressure. In the 1930s, endocrinologist Hans Selye revived this use of the term to include physiological reactions to outside forces acting on the body, such as heat, cold, and injuries that lead to pain. It wasn’t until the 1960s that we began to use the word the way we use it today, to mean the psychological tension we feel from anticipating adverse events, and the biological correlates of them.

You may be familiar with homeostasis, the idea that the body seeks to maintain consistency, say, in core temperature, or blood levels of oxygen.

In the last twenty years, though, we’ve recognized that levels of some of our physiological systems—such as blood sugar levels, heart rate, blood pressure, and respiration rate—require continual adjustment to function optimally. This idea of stability through change is called allostasis—systems fluctuating regularly in response to life’s demands.

When a situation is perceived as being stressful (because it is novel, unpredictable, uncontrollable, or painful), two major classes of stress hormones are secreted, catecholamines and glucocorticoids. They are the first hormonal systems to respond to stress. The short-term secretion of these hormones in the face of a challenge serves an adaptive purpose and leads to the fight-or-flight response (allostasis). However, the same stress hormones that are essential for survival can have damaging effects on both physical and mental health if they are secreted over a longer period of time (called allostatic load). This happens because when these primary stress hormones are increased for long periods of time, it leads to dysregulation of other major biological pathways in the body and the brain, for example, insulin, glucose, lipids, and neurotransmitters. This in turn causes a dysregulation of various other operations, such as the immune system, the digestive system, the reproductive system, cardiac health, and mental health.

Your allostatic load is the cumulative effect of stress over time; it indexes your changes in various biomarkers of stress (blood sugar, insulin, immune markers, stress markers, etc.) in response to the events of your life. Your allostatic load can be calculated by looking at levels of certain “stress biomarkers,” including C-reactive protein, insulin, blood pressure, and so on. Social support is a strong predictor of allostatic load, with those having less social support showing the highest load. This is another case of not knowing the direction of causality—does having few or no friends increase stress? Probably. Does being stressed to begin with drive friends away? Probably. Does not having friends to comfort you cause that stress to linger instead of dissipating? Again, probably.

There are many ways to reduce stress, of course. Cognitive behavioral therapy (CBT), a form of talk therapy that teaches tools to help you cope, is one of them. Exercise, meditation, listening to music, immersing yourself in nature, and sometimes just talking to friends and having social support can help to reduce stress significantly.

If emotions are constructed, like perceptions, you might think that the brain tries to fill in and predict what is going to happen next to us emotionally—and it does. For most of us, our bodies seek to maintain a kind of emotional consistency; we internally regulate our emotions so that we don’t experience extremes, because they can be emotionally and physiologically overwhelming. The central nervous system learns to anticipate stressors and to make allostatic adjustments in advance. The entire process is dynamic—it is an adaptable, plastic system that responds to sensory perceptions and cognitive processing by regulating neurotransmitters and hormones to either produce or recover from stress.

Part of effective regulation is the reduction of uncertainty. Our brains try to anticipate the outcome of future events, to anticipate our needs and plan how to satisfy those needs in advance. Doing this is metabolically expensive if your life is marked by great uncertainty, and the brain can easily use up its resources, resulting in a harmful increase in allostatic load. Because allostasis is a predictive system, it can be influenced or miscalibrated by early life stressors or extreme traumas. A stable fetal and early childhood environment can lead to a well-functioning allostatic system. But adverse childhood experiences can result in a system that either overreacts or just shuts down in response to what might otherwise be considered normal daily ups and downs, creating hypervigilance, reduced resilience, and sometimes wild mood swings—a lifetime in which normal allostatic regulation is never reached. Someone who has grown up in adverse conditions will have long-term memories that contain threatening and stressful information; their default prediction for even neutral events is that something bad could happen, and this kicks in their stress response, releasing cortisol and adrenaline in advance of a great many situations that are benign. On a systems level, we’d say that they are not regulating their HPA (hypothalamic-pituitary-adrenal) axis—the body’s stress response system.

When we lack this kind of regulation, because either our lives are chaotic or our neurochemical systems are not properly calibrated, we can experience mood swings; we can act irrationally or impulsively, causing ourselves harm; and we can experience a range of illnesses, diseases, and other problems across the life span. Increased allostatic load (and the resulting loss of hormone regulation) can lead to cardiovascular disease, diabetes, compromised immune function, and cognitive decline. It has also been linked to a number of psychiatric conditions, for example, depression and anxiety disorders, and burnout and post-traumatic stress disorders.

Elevated cortisol levels in response to early life stress have been linked to accelerated hippocampal atrophy among both healthy individuals and people in the early stages of Alzheimer’s disease. Thus, successful emotion regulation may protect not only older people’s physical well-being but their mental capacities as well.

There are many factors that influence the stress response and the health of the allostatic system—it’s not just the obvious things like a mother who took drugs during pregnancy or an early toddlerhood surrounded by domestic violence. These factors include:

  • demographics, such as age, sex, socioeconomics, education;
  • developmental conditions, such as poor parental attachment, chronic illness, being bullied;
  • genetics, such as telomere length, cortisol insufficiency, deficiency in angiotensin converting enzyme (which regulates blood pressure);
  • environment, such as culture, extreme climates, smoking behaviors, famine;
  • neuroendocrine functioning; and
  • psychological factors, such as locus of control, and the tools we bring to emotional regulation.

But not everyone with a stressful childhood ends up with a psychiatric disorder, or even a high allostatic load. Stressful experiences can lead to very different outcomes, depending on the interaction of the factors listed above. Some people develop resilience, grit, tenacity, and focus. Others fall apart. The prized combination that allows some people to live more positive lives, to turn lemons into lemonade, is still unknown and an active topic of research. One thing we do know is that thoughtful parenting and/ or education can put people on the more positive path and give them better overall life outcomes, reducing the disadvantages caused by childhood adversity.

From Successful Aging by Daniel J. Levitin, published on 1/7/20 by Dutton, an imprint of Penguin Publishing Group, a division of Penguin Random House, LLC.  Copyright (c) 2020 by Daniel J. Levitin.

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