Thank you Heidi Krol, Jay Clapp, Janie McManus, Rosemary, and many others for tuning into my live video with Chris Miller MD!
Cold Water, Real Talk: What Chris Asked Me (and What the Science Suggests)
Chris Miller MD interviewed me on Substack, which was a nice change, because I’m usually the one asking her the questions. She asked the things people actually want to know: why cold water is suddenly everywhere, what it does in the body, and whether you really have to suffer for three minutes to get any benefit.
If you watched the live, this is the written version to sit under the video. If you have not watched yet, the video is right above this post.
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Why I wrote a cold water series (click here to find the series)
Cold water exposure has been around forever. What’s new is how loud it has gotten online. Once something turns into a trend, it’s easy for claims to outpace evidence. That’s usually where I step in.
I pick topics based on what readers ask for, what I’m curious about, and what seems useful enough to justify the time it takes to research properly. Cold water kept coming up in reader prompts and in conversations at home. So I decided to do a deep review.
Then I started reading the research and realized one article would be too small for what I was finding. That’s why it became a five-part series.
The Dutch shower study that caught my attention
Early on, we talked about a study out of the Netherlands that used a simple approach. People took their normal warm shower, then switched to cold water at the end for 30, 60, or 90 seconds. They did that for 30 days.
What stood out was what happened after the study ended. A majority kept doing the cold finish. The figure I shared on the live was 64%. These were not people who were already doing ice baths. They were regular participants who tried something uncomfortable and chose to keep it.
They reported feeling better. That does not explain the mechanism by itself, but it does raise a worthwhile question. Why would someone voluntarily keep doing something unpleasant unless they felt a benefit on the other side?
My longest cold exposure habit is not a plunge
I shared a personal story that surprised me once I said it out loud.
Growing up, we had one bathroom. The rule was no morning showers for kids under 18. Everyone showered at night. In the morning, I started splashing cold water on my face to wake up. I’ve done it ever since. I’m 55 now, and it’s still part of my morning.
I never labeled it as “cold exposure.” It was just practical. When I started researching cold water physiology, it made me look at that habit differently. It also made me think about why it has always felt so effective.
Cold exposure has a long history, even if the hype feels new
Cold water therapy is old. Hippocrates wrote about water-based treatments. Roman bathhouses had cold plunge pools, the frigidarium, built into the routine. In later centuries, physicians experimented with cold water in ways that would not be acceptable today.
What’s different now is measurement. We can track heart rate, blood pressure, inflammatory markers, metabolic changes, and signaling chemicals in the blood. That helps separate “people say it works” from “here’s what the body does when it happens.”
The first minute can feel brutal for a reason
Chris and I spent time on what happens in the first 60 seconds because that’s the part that scares people.
Cold water can trigger the cold shock response. You gasp. Your breathing gets jagged. Your heart rate jumps. Your blood pressure rises. Your body reads the situation as a threat.
I told a story from a Spartan race in Snowmass where one obstacle involved getting into an ice-filled container and going under a bar to the other side. The first time I went under, I hit my head, came up, and realized I hadn’t made it through. That meant I had to go back under while already stressed and short of breath.
Then a man blocking the exit asked me to retrieve his headband from the ice water.
That was a firm no.
The point is simple: the cold shock response is real and intense. If you have ever jumped into a cold river and felt your chest tighten or your breath catch, you’ve experienced the basics of it.
Why some people feel calm right after feeling panicked
Right after the shock, another reflex can kick in, especially when cold water hits the face.
It’s called the mammalian dive reflex. In plain language, it’s a built-in system that helps conserve oxygen during submersion. It can slow heart rate and shift the body toward a calmer state.
That creates a strange overlap where the stress response is firing while a slowing response is also turning on. I used the term autonomic conflict in the live, meaning two opposing systems are active at the same time.
This helps explain why people describe cold exposure as intense at first and then oddly settling.
Do you have to stay in for three minutes?
Chris asked the question most people ask: if you jump in and jump out, do you still get anything, or do you have to stay in for the full “three minutes” people talk about online?
My answer was: it depends on your goal, your safety profile, and what you can tolerate consistently. That’s why the fifth article in the series is a protocol piece with options.
For some people, cold water on the face is plenty. For others, a short cold finish to a warm shower works well. For others, full immersion is the tool they want.
We also talked about cold air exposure. Water pulls heat from the body much faster than air, but some research suggests cold exposure in general can improve insulin sensitivity, likely through activation of brown fat.
Brown fat is not the fat most people think of
Brown fat is metabolically active tissue that helps generate heat. It is different from white fat, which is primarily storage. When brown fat is activated by cold, it takes up glucose and fats from the bloodstream and burns them to produce heat. That process can improve insulin sensitivity over time.
This is one of the most plausible explanations for why cold exposure is studied in metabolic health.
Immune effects: less sickness or better tolerance?
People often say cold plunges “boost immunity.” That’s not a clean claim, and it depends on what someone means by “boost.”
Cold exposure is a stressor. It can raise inflammatory markers in the short term. With repeated exposure, the body may adapt and become less reactive. People may not get sick less often, but they may handle stress and illness differently.
Chris framed this through hormesis, meaning a controlled stress that can lead to beneficial adaptation when the dose is appropriate. Like exercise.
The neurotransmitter piece helps explain why people keep doing it
Chris brought up her favorite section of the series: neurotransmitters.
I talked about studies where short cold water exposure was followed by large increases in norepinephrine, sometimes reported in the 200% to 300% range in some individuals. Norepinephrine is tied to alertness and focus. It’s one reason cold can feel like flipping a switch.
Dopamine tends to rise more gradually and can stay elevated longer. Dopamine supports motivation and drive. Some people describe an “after effect” that lasts. This may be part of it.
Endorphins also rise. These are opioid-like chemicals your brain produces that can reduce pain perception and lift mood.
When you combine increased alertness with a mood lift, it makes more sense why someone finishes a cold shower and says, “I feel clear.” They’re not imagining it. Their body chemistry has shifted.
Chris also asked about timing. Morning or evening? Research does not consistently show sleep disruption for everyone, but because cold exposure can be stimulating, many people do better earlier in the day, especially if they’re sensitive to stimulation or already use caffeine.
A key caution for strength training
I also flagged an important nuance.
If your goal is muscle growth and strength, doing cold water immersion immediately after lifting may blunt some of the adaptive response. Post-exercise inflammation and blood flow are part of how muscle rebuilds. If you reduce that response right away, you may reduce some of the gains you are training for.
That does not mean cold exposure is “bad.” It means timing matters. An in-season athlete trying to recover for the next game has a different goal than someone training to build strength in the off-season.
Who should avoid cold immersion
Chris emphasized safety, and she was right to do it. Cold shock can increase heart rate and blood pressure. That can be risky for some people.
I previewed that the next article in the series covers who should avoid cold water immersion and why. I also mentioned a reader comment about neurodivergent individuals who may find cold exposure dysregulating. For some people, “pushing through” is not the right approach. Modifying the exposure, or skipping it, can be the safer choice.
Cold exposure is a tool. It’s optional.
Poetry vs plumbing
Near the end, I shared an idea I heard on a podcast: people love the poetry of a big goal, but they forget the plumbing. The plumbing is the boring system that makes the goal work.
That concept applies to health goals every January. People announce a big outcome, then skip the daily structure that would make it possible.
For some people, cold exposure can function as part of the plumbing. Not because it’s magic, but because it’s a simple lever that may support alertness, mood, and resilience. It can be built into a day without turning into a whole identity.
What’s coming next
The cold water series continues with an article focused on risks and who should avoid it, followed by the final article with protocols based on goals and tolerance.
I also shared what’s ahead more broadly: deeper monthly topic series that end in mini-courses inside Substack for paid subscribers, more “learn your body” content in a mini medical school style, daily tiny habit posts for people who want the simplest version, and a short weekly meditation experiment with a transcript included.
And yes, I’m working on a book proposal too.
The takeaway
Cold water is not required. It’s not a badge. It’s one more lever some people can use.
For the right person, used the right way, it may support focus, mood, and metabolic flexibility. The key is matching the tool to the person, the goal, and the realities of their health and nervous system.
That’s the work. Tools, used wisely.
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