Understanding Our Stress Response System

What can it can show us about health and illness?

The next time you listen to Beethoven’s Ninth or your favorite symphony, try listening to it as an everyday miracle of musical evolution. Picture eons ago, in the Rift Valley perhaps, there was a voice. And a drumming foot. And then a reed to match the voice and the drumming foot. Several voices and feet found a rhythm and a song.

Over the generations, toolmakers strung gourds with vines or strands of hide. And as the musicians and instruments multiplied—vocal, percussion, wind, and strings—they tuned each other across the range of simple and evermore complex musical explorations, creating, eventually, orchestras and symphonies.

And the next time you witness a healing—from a simple cut with a kitchen knife or a recovery from stage IV cancer—try thinking of it as an everyday miracle of human evolution. It’s harder to picture this kind of evolution, the way our stress response system came to be, not only because it is so much more complicated than music, but also because our stress response system remains invisible and inaudible, a mystery to modern medicine.

Though we all talk a lot about stress, most doctors don’t measure stress and don’t know how to treat toxic stress. Even mental health specialists (psychologists, psychiatrists, and other therapists) don’t measure stress in any standard or comprehensive way. No wonder we have a hard time understanding how stress leads to illness and what we can do to change that.

The urgent need to achieve clarity about the stress response system is rooted in the mysterious rise over the past forty years—the blink of an eye in evolutionary terms—of common stress-related conditions in the U.S. and much of the developed world: suicide, addictions, depression, obesity, diabetes, heart disease, attention deficit hyperactivity disorder, post-traumatic stress disorder, and autoimmune disorders. The pathophysiologies of these conditions could not be more different from each other, yet all have been shown to increase in frequency after exposure to toxic stress. They remind us that there are many ways to dysregulate the stress response system, most of which lead to early death.

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An Orchestra of Organs

Part of the complexity of the stress response system lies in its being a system of systems, as complex and interdependent as our planet’s ecosystem, as harmonious and sometimes unruly as an orchestra. Although under extreme demands the stress response system activates all organs, six main organs do the bulk of the work to keep us alive during daily hassles as well as life-threatening dangers: 1) the brain and nerves, 2) the cardiorespiratory system, 3) the stress hormones, 4) the immune system, 5) the gastrointestinal system, and 6) the musculoskeletal system.

To appreciate what an everyday miracle this system is, think about how evolution has selected for these distinguishing features.

It’s essential. We can’t live without it. Its purpose is to respond to the demands of life. When it works well, we feel healthy, and when it breaks down, at first we feel distress, then maybe ill, then, if we don’t recover, we die. Our stress response system is as primitive as the primates’ and as sophisticated as our brains.

It’s self-regulating. No user manual needed. Through a complex set of feedback loops, each organ system automatically keeps itself operating within certain limits compatible with life. The coordination of these systems—the unseen conductor of the orchestra—happens deep in the unconscious regions of the central nervous system and in the peripheral and autonomic nervous systems, which reach into every organ of the body. Any organ that strays beyond these limits raises show-stopping alarms in the form of fevers, fainting, racing heartbeats, or weakness, for example. The whole system is designed to maintain homeostasis, or steady functioning within healthy limits for all organ systems.

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It has cycles of work and rest. Just as the heart functions best when it alternately contracts and relaxes at about 60 cycles per minute, the whole stress response system functions best through cycles of work and rest. Some of these cycles take seconds (heart beats), minutes (respirations), hours (hunger), or a day (sleep). Through these cycles of work and rest, the stress response system regulates itself at the tissue, organ, and macrosystem levels. Stressors that persistently disrupt this self-regulating process may lead to a variety of illnesses.

It’s always on alert. Evolution has selected for a stress response system that is always ready to jump into action, assuming our environment is unsafe unless proven otherwise. Our prefrontal cortex restrains our fight or flight response in safe settings, and the vagus nerve keeps the sympathetic nervous system in check. Vagal withdrawal is the first step in releasing the stress response, like a truck releasing its brake on a steep slope. Sympathetic activity then jolts us into action, and adrenaline and cortisol come slower to the organs to keep us going till the demand is met.

It’s redundant and elastic. Redundancy is one of nature’s ways of achieving resilience. Our bodies are built with plenty of extras, and each organ system can, to some extent, cover for another, the way ten violinists can cover for one fainting violinist. And each of these organ systems is impressively elastic, as opposed to rigid. The cardiovascular system, for example, can function with as much as 5.5 liters of blood and as little as 4.5 liters. Heart rates can triple during exercise, and heart rate recovery during rest is a good measure of the resilience of the cardiovascular system.

Miracle and Mystery

About one in five of us is exposed to toxic stress of one kind or another: trauma, poverty, abusive relationships, multiple chronic conditions, discrimination, or prison, to name a few. How toxic stress turns to illness and how it accelerates aging are some of the most pressing mysteries of modern medicine. How do we know who will get sick or die young? Through a series of deep dives into the miracles and mysteries of the stress response system, I hope to challenge us to do a better job of measuring stress, managing stress-related conditions, and advocating for stress neuroscience as a high public health priority.

Pearl: Looking at health and illness through the lens of the stress response system offers new approaches to our most common and costly health problems.

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