Why You Cannot Switch Off, and How Cold Resets Your Nervous System
The problem was never how much stress you meet. It is whether your body ever finishes it.
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I have come to believe that most people do not have a stress problem. They have a resolution problem.
We talk about stress as though it were a substance, something that piles up until we reduce it. But from a physiological point of view, stress is not a quantity, but a signal. A deviation from your body’s current state that sets off a response. In a healthy system, that response rises, does its job, and then resolves. You return to baseline.
The trouble begins when the return does not happen. When the signal fires and fires and never lands back down. That is the state I want to talk about, and it is also where cold and heat become genuinely interesting, because they are two of the few tools I know that train the resolution itself.
Let me show you the science I find most persuasive, and then tell you what I think it means.
What the cold does to your stress chemistry
In 2000, a group of Czech physiologists ran a careful experiment [1]. They put young men into water at three different temperatures, 32°C, 20°C, and 14°C, for one hour each, and measured what happened to their hormones and cardiovascular system.
The 14°C immersion is the one people quote, and for good reason. Noradrenaline, the alerting, focusing catecholamine, rose by 530%. Dopamine rose by 250%. Those are not small numbers. That is your nervous system, told in the bluntest possible terms that something demanding is happening, releasing the exact chemistry of alertness and drive.
Here is the part that gets left out, and the part I find more important. In the milder immersions, cortisol, the hormone we most associate with chronic stress, did not climb. It tended to fall. Heart rate and blood pressure dropped. So cold water is not simply a stressor that floods you with stress hormones. It produces a sharp, clean activation of the alerting system while the deeper stress axis stays calm or settles.
That combination, high alertness without a cortisol surge, is exactly the profile of a stress response that is designed to resolve. And that is why I keep returning to cold as a training tool rather than a punishment.
Why the recovery matters more than the shock
My own research points the same direction [2]. We studied experienced winter swimmers, men who combine cold dips with sauna two to three times a week, and compared them with people who did neither.
What struck me was not that the swimmers had some dramatic advantage in brown fat activity. They did not, by the measure of glucose uptake. What they had was better thermoregulation. Their bodies handled the swing between cold and heat more efficiently, with a higher cold-induced heat production and a calmer overall response. They had, in a word, adapted. The practice had trained the system that manages the challenge and the return, not just the moment of shock.
That is the whole thesis. The adaptation is not in how hard you can hit yourself with cold. It is in how well your body learns to respond and then come back down. Cold and heat, used deliberately, are rehearsal for resolution.
Do you want to build the practice?
Understanding how stress resolves is one thing. Building the practice that trains it is another. If you want the guided version, the Søberg® 12-Week Reset is the program I built for exactly this: a week-by-week journey through cold, heat, breathwork, sleep, movement, and nervous system regulation, designed to help you build a stress-resilient body that actually fits your life. It is at soeberginstitute.com if you would like to go deeper.
Where this goes deeper
In the companion piece for members, I go the whole way into the physiology of resolution: what happens inside the body when a stress response ends, why McEwen’s concept of allostatic load explains so much of modern exhaustion, and how the settling window after cold is the part almost everyone wastes.
In the full piece you will get answers to:
Why “reduce your stress” is the wrong goal, and what allostatic load reveals about the real problem
What a 530% noradrenaline spike with calm cortisol means for your nervous system
Why the winter swimmers’ real advantage was in recovery, not in how much cold they could take
The settling window almost everyone skips, and how to protect it
How to tell whether a session resolved or quietly left you wired all day
When cold is the wrong tool, and pushing through does harm
If this is the kind of thinking you want more of, that piece is where it lives.
How to Use Cold to Build a Stress-Proof Nervous System
For members. Thank you for being here. This is the deep dive, with the exact steps, and it exists because you support my work. You can read everything in the archive and the Journal, any time. Enjoy.
The plate that goes with this
Resolving stress is not only a nervous system practice. It is also what you put on your plate at the end of a hard day.
This week on The Søberg® Plate I have shared a supper built for exactly this: salmon and white beans in a warm broth, with wilted greens and toasted pumpkin seeds. It is built around magnesium and glycine, the two nutrients most tied to calm and to sleep, in food form rather than a capsule. Warm, protein-rich, and easy to digest before bed, so it supports the shift out of stress and into rest.
The full recipe, with the science behind each ingredient, is here:
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Dr. Susanna Søberg, PhD
References
[1] Šrámek P, Šimečková M, Janský L, Šavlíková J, Vybíral S. Human physiological responses to immersion into water of different temperatures. European Journal of Applied Physiology. 2000;81(5):436-442. doi:10.1007/s004210050065
[2] Søberg S, Löfgren J, Philipsen FE, et al. Altered brown fat thermoregulation and enhanced cold-induced thermogenesis in young, healthy, winter-swimming men. Cell Reports Medicine. 2021;2(10):100408. doi:10.1016/j.xcrm.2021.100408