I read Why Zebras Don’t Get Ulcers about eight years ago, and the image at its centre has never left me.
The zebra is chased by a lion. The chase ends. The lion moves on. And within minutes, the zebra is back to grazing, calm, regulated, physiologically reset. The stress response has done its job. The body has returned to baseline. The cycle is complete.
Most of us are not like this. We keep running from lions that are no longer there. The threat has passed, sometimes by years, sometimes by decades, but the body never received the signal. So it goes on reacting to the present through the filter of everything that came before. The nervous system stays braced. The stress hormones keep circulating. The inflammatory machinery stays switched on, at a low hum, long after the original danger has gone.
Anaïs Nin captured something true when she wrote: “We don’t see things as they are, we see them as we are.” The nervous system operates the same way. It does not evaluate the present moment objectively. It evaluates it through the accumulated archive of every prior experience, particularly the threatening ones, and responds accordingly.
This is personal
I do not write about chronic stress from a position of clinical distance. Athlete. Childhood trauma. Long COVID. Immune dysfunction. Chronic stress has been written into my own biology over a very long time. I know what it looks like on a blood test, the elevated cortisol, the flattened HRV, the inflammatory markers that resist resolution, and I know what it feels like from the inside: a body running hot, a nervous system that does not know how to rest, a background sense of urgency that persists even in objectively safe circumstances.
I also see it every week in clinic, in people whose external presentation tells a very different story.
Fatigue that sleep doesn’t touch. Insomnia that persists despite good sleep hygiene and adequate wind-down routines. Anxiety that hums underneath everything, present in moments of calm, present in moments of achievement, present at 3am with no particular stimulus to explain it. An autoimmune flare that traces back, when you look carefully at the timeline, to years of never quite feeling safe. And then there is the binge eating, the compulsive scrolling, the second glass of wine, the small habitual addictions that we reach for not because we are weak but because the nervous system is looking for any available mechanism to take the edge off a load it cannot otherwise metabolise.
These are not character flaws. They are coping strategies that developed for good reasons and that have often outlasted the conditions that required them. And beneath all of them is the same biological story: a nervous system that never found its way back to the grass.
What happens inside when stress hits
Before we discuss what happens when stress becomes chronic, it helps to understand what the acute stress response is actually doing, because it is, in isolation, a brilliant piece of biological engineering.
When a threat is perceived, the body runs one ancient programme, regardless of whether the threat is a lion or a 3am spiral about money. Adrenaline and cortisol surge. Heart rate and blood pressure climb. Energy floods the muscles. Digestion pauses. Immune defences take a back seat.
This is exactly the right response for a three-minute emergency. It mobilises every available resource and points it at survival. The zebra needs to run, and the body delivers everything required to run as hard as possible.
The problem emerges at the other end of the timeline. We do not face many lions. But we switch on the very same programme for a full inbox, a traffic jam, a hard conversation, the 3am “what if” that arrives with no particular trigger and refuses to leave. And crucially, unlike the zebra, whose nervous system knows that the danger has passed and transitions back to grazing, we leave the programme running for years.
What chronic stress does to the body
The science here is unambiguous, well-documented, and deserves to be communicated plainly.
When the stress response, mediated primarily through the HPA axis (hypothalamic-pituitary-adrenal axis) and the sustained elevation of cortisol, becomes chronic rather than episodic, the entire regulatory system begins to dysregulate. This is not metaphorical — it is a measurable cascade of biological events with far-reaching consequences.
Cortisol rhythms flatten. The healthy circadian pattern, a robust morning peak that provides energy and immune activation, declining across the day to a low evening baseline that permits genuine rest and repair, becomes disrupted. Over time, glucocorticoid receptors become progressively less sensitive to cortisol, requiring the body to produce more of it to achieve the same regulatory effect. This creates a vicious cycle in which the very hormone meant to regulate the stress response becomes part of what sustains it, driving pro-inflammatory signalling rather than dampening it.
The downstream effects are systemic. Stress hormones running non-stop quietly tax the heart and blood vessels, the gut, the immune system, memory, and the brain. As immune dysregulation follows, elevated inflammatory markers, CRP, IL-6, and others, create a tissue-damaging low-grade inflammatory state. Sleep architecture deteriorates, particularly the deep slow-wave phases in which the most critical cellular repair processes occur. Beyond that, glucose metabolism and insulin sensitivity are impaired, and gut function is disrupted through the gut-brain axis, affecting the microbiome and intestinal barrier integrity.
Chronic stress is not “in your head.” It lives in your body, written into the physiology.
A brief but important aside on this: the carousel that inspired this post references stomach ulcers, and it is worth being precise. Most stomach ulcers are caused by H. pylori, a bacterium, not stress alone. But chronic stress does leave the gut more vulnerable: it increases gastric acid output, impairs mucosal repair mechanisms, and slows healing once injury occurs. The title of Robert Sapolsky’s book, Why Zebras Don’t Get Ulcers, is partly a hook. The biology underneath it is genuinely real. And intellectual honesty about where the metaphor ends and the mechanism begins is, I think, part of what makes the stress conversation clinically useful rather than merely rhetorical.
The autoimmune connection
Research published in major journals in 2024 and 2025 has found that chronic HPA axis dysfunction is now clearly associated with autoimmune conditions including systemic lupus erythematosus, rheumatoid arthritis, and multiple sclerosis, conditions historically understood as primarily immunological, but increasingly recognised as having significant neuroendocrine drivers.
The nervous system is not a peripheral concern in health and longevity. It is the conductor of the orchestra. And when the conductor is running a chronic emergency programme, every section is affected.
We have optimised ourselves into depletion
Here is what genuinely troubles me about much of contemporary wellness culture.
We have become extraordinarily skilled at adding. More tracking, more supplements, more protocols, more cold exposure, more time-restricted eating, more output, more data, more optimisation layers stacked on top of each other. The wellness industry has built an entire economy around this impulse, and it is not without value — some of these interventions are genuinely useful.
Yet almost no one is asking what it would mean to subtract. To genuinely rest. To stop. To allow the body to complete the recovery cycle it is built for rather than perpetually interrupting it with the next intervention.
The disease, and I mean this literally, physiologically, does not come from stress itself. Stress is unavoidable, and appropriately managed, it is the driver of adaptation and growth. The disease comes from the chronic absence of ease. From never allowing the system to come down. From treating rest as a reward earned by sufficient output rather than a biological requirement as non-negotiable as food or water.
Constant motion has been mistaken for progress. We have dressed up our inability to stop as discipline, as productivity, as optimisation. Meanwhile, the body, running silently beneath all of it, unable to enter the repair state it needs because the performance never pauses, has been keeping score in the only language available to it: physiology.
The work is learning how to graze
I do not believe the goal is to eliminate stress. Some stress is not only unavoidable but necessary, it is the mechanism through which the body builds resilience, through which we develop genuine capacity, through which adaptation and growth occur. A life without stress would not be a healthy one.
The work is developing the capacity for ease alongside the capacity for effort. Learning, again, because for most of us this was once more natural than it has become, how to actually rest. How to let the body move through the repair cycle it was designed for. How to allow the nervous system to genuinely come down, rather than sedating it temporarily and calling that rest.
What the biology of repair requires
What this looks like in practice varies by person, but the biological building blocks are consistent: genuine, pleasurable movement rather than compulsive exercise driven by anxiety. Authentic human connection, the kind that involves real presence, real conversation, real contact, rather than its digital approximation. Rest that is actually restorative: the parasympathetic state in which cortisol falls, HRV rises, cellular repair is activated, and the nervous system genuinely settles. And the felt sense of safety, the thing that allows the autonomic nervous system to release its defensive grip and permit the body to rebuild.
These are not luxuries to be earned by sufficient productivity. They are the biology of repair. And without them, no amount of supplementation, no panel of biomarkers, no optimisation protocol will fully deliver what it promises.
If you have forgotten how to graze, if rest feels unearned, if stillness produces anxiety rather than relief, if you cannot remember the last time you were genuinely present in your own body without an agenda or a target, that is information worth taking seriously. The body is communicating something important.
You cannot avoid stress. That is not the goal, and anyone selling that promise is not being straight with you. But you can stop being a zebra that never stops running. The prescription, for all its apparent simplicity, is grounded in genuine physiology: pause. Graze. Breathe.
The lion has probably gone. The question is whether your nervous system has received that message, and whether you are giving it the conditions in which it can.
At Wellgevity, we work with people who are high-functioning and yet not fully well, people whose biology tells a more complicated story than their achievements suggest. If you would like to explore what a whole-systems approach to your health might look like, you can apply to work with us here.
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