I like my nervous system feeling supported, not shocked. Last week, whilst I was in Chicago, a cold front rolled in and dropped temperatures below minus 20!! Despite the warnings to stay indoors, I went for a walk.
I’ll be honest with you. I am not a natural cold lover. Give me a sauna over a cold plunge any day. I like warmth. I like my nervous system feeling supported, not shocked.
And yet.... Last week, whilst I was in Chicago, a cold front rolled in and dropped temperatures below minus 20!! Despite the warnings to stay indoors, I went for a walk. After all, I couldn't be a first timer in Chicago without seeing Lake Michigan could I? It was frozen and beautiful and mesmerising!
And that walk in the crisp air under a clear blue sky did something.
It invigorated me. Despite my painful eyeballs (the only part of me that I'd left exposed!) I came back inside after a 2h walk energised and clear-headed. Switched on. Not the bravado version. The biological one. Let’s dive in...
Where insight becomes impact
What I’ve been looking at this week…
Cold exposure is one of the most hyped and misunderstood tools in health and wellness. You’ve probably heard claims about boosting immunity or ramping metabolism from ice baths and cold showers. The effect is a little more nuanced than that. And many people think cold exposure is about willpower or resilience. Or pushing through discomfort. That’s the wrong frame.
Cold is a signal, not a punishment.
One of the best-known studies on cold showers comes from the Netherlands. Over 3,000 people were asked to finish their daily shower with 30, 60, or 90 seconds of cold water for 30 days. The headline result was a 29 percent reduction in sickness absence from work.
Here’s the detail most people miss.
There was no difference between 30, 60, or 90 seconds.
Which tells you the benefit isn'tabout endurance. It's about activation.
Cold exposure activates a rapid rise in noradrenaline, a brain chemical released during stress, involved in alertness, focus, and immune signalling. It also triggers a short-term inflammatory response. That sounds counterintuitive - more stress, more inflammation - but it’s exactly how hormesis works. A brief stress teaches your system to respond better next time - that's resilience.
This also explains an apparent contradiction in the study. Illness days didn’t reduce, but sickness absence did. Which means cold exposure doesn’t necessarily stop you getting ill, despite claims of boosting immunity. What it does instead i change how incapacitated you feel when you are iill, meaning it allows you to keep functioning.
At a cellular level, cold nudges cells into protection mode. Cold exposure switches on cold shock proteins, especially one called RBM3. These proteins help stabilise cellular instructions when the cell is under stress, supporting repair and maintenance.
Cold also activates brown fat, a special type of fat whose job is to generate heat. To do that, it burns glucose and fatty acids. When brown fat is activated regularly, the body becomes better at using fuel efficiently, switching between sugar and fat more smoothly. That’s what we mean by improved metabolic flexibility.
One important nuance though.
Men and women respond differently to cold. Women often get a stronger stress signal at lower doses.
Which means more intensity is not better. Appropriate intensity is.
Track it to hack it.
What I’ve been monitoring this week…
I think about cold exposure devices in the same was as medication. The dose matters.
There are fantastic cold experiences you can create in your own home or visit specific facilities for this. The important thing is to consider dose, duration and timing.
Low-dose : gentle signalling This is where most people should start and where many should stay.
Examples Cold air exposure, cool to cold showers, cryo wraps or ice packs, handheld cold jets. Dose 30 seconds to 2 minutes 3–5 times per week
Why it works Brief cold exposure increases norepinephrine and trains the nervous system without provoking a large cortisol stress response. This explains why cold shower studies show benefits with very short exposures and no added gain from longer durations.
Medium-dose cold: whole-body adaptation This is a stronger, more demanding signal.
Examples Cold plunge pools or ice baths.
Dose 8–12 °C 1–3 minutes 2–3 times per week 6-10 minutes per week
What the data shows
Rapid norepinephrine release within the first 30–90 seconds
Peak autonomic and vascular response by 2–3 minutes
No additional metabolic or immune benefit beyond 3–5 minutes
Longer immersions mostly increase discomfort and risk, not benefit. No additional benefits from daily plunging. This dose activates brown fat and metabolic flexibility best,
High-intensity cold: short and sharp
Examples Cryotherapy chambers.
Dose −110 to −140 °C 2–3 minutes 1–3 times per week Best thought of as a brief neurochemical stimulus.
The mistake I see most often People jump straight to medium or high doses without ever establishing tolerance or need. That’s like starting a medication at the maximum dose and wondering why you feel awful. It could leave you:
Wired
Exhausted
Irritable Sleeping poorly
The principle I use Low dose cold = nervous system training Medium dose cold = metabolic and vascular adaptation High dose cold = short-term neurochemical stimulus Different tools. Different jobs.
More minutes does not mean more benefit Cold works when it’s precise, not extreme.
From knowing to doing.
What this means for YOU…
Cold exposure is a stress stimulus. That’s the point. It means cold should be mapped to the stress signals already present in your body, not added on blindly.
Start with your cortisol rhythm.
If cortisol is high in the morning, and you're waking feeling wired, alert but anxious, or tired yet unable to slow down then cold first thing can amplify stress. Instead light, movement, and warmth on waking is preferable, and placing cold later in the day once cortisol has fallen.
If cortisol is low or blunted in the morning, and you tend to wake groggy, heavy, or foggy, then cold earlier in the day can act as a useful wake-up signal, improving alertness without overstimulation.
Night-time matters too. Cold late in the evening often disrupts sleep, even if it feels calming in the moment. If cortisol is high at bedtime or sleep is fragile, cold belongs earlier, not as a wind-down tool.
And if you're strength training regularly, timing matters. Cold immediately after heavy strength work can blunt muscle adaptation, so it’s best separated from lifting days if muscle is a goal.
For women, the menstrual cycle matters. Cold is often better tolerated in the follicular phase just after a period. In the luteal phase, just after ovulation, when body temperature and stress sensitivity rise, shorter or less frequent cold usually works better.
How do you know if cold is helping? Don't guess. Monitor the response.
Track:
HRV for stress resilience
Resting heart rate for stress load
Sleep architecture, especially deep sleep and awakenings
Morning energy and emotional reactivity
If cold is working, sleep improves and energy stabilises. If it’s not, you’ll feel wired, flat, or sleep will suffer. Cold isn’t something you just add. You map it, then you monitor it.
Case In Point 👝 A founder I work with was doing cold plunges every morning to build resilience. I tested her cortisol curve (saliva test, sent to her home with saliva collection 4 times through the day) Her curve was steep with high cortisl levels in the morning. We didn’t remove cold. We moved it. Morning cold stopped. Cold shifted to later in the day, frequency reduced, and evenings protected for sleep. Within weeks, HRV improved, sleep consolidated, and her energy stopped swinging.
Same tool. Different timing. Completely different outcome.
🎯 If you'd like to make decisions with precision based on your personal data and using devices that are specific for you, then book a private consultation and let's start to decode your health.
Where you’ll find me…
Last week: Been speaking in some great venues- Soho House, Pavilion and The Amex Stadium. Love live conversations that get people thinking differently about their health.
This week: Am stateside in the US!
Next week: Back in London, consulting and in clinic.
A thought to pause on…
“Cold doesn’t build resilience. Correctly timed cold does."
Wishing you a wonderful week ahead (that's 168 hours of your Million Hour life!! Dr Alka
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Take the free LQThis article is general education, not medical advice, and reading it does not create a doctor-patient relationship. If something has been going on for a while, please get it properly looked at by your own doctor.