The first time the ten men in the study got into 14°C water, their cells got worse. Markers of autophagy, the process by which cells identify and recycle their own damaged components, dropped. Markers of programmed cell death rose. Inflammatory signalling increased. By every measure the researchers tracked, that first cold exposure suppressed the cellular cleanup it was supposed to trigger.
Seven days later, after daily immersions in the same water at the same temperature, those same markers had reversed. Autophagy was enhanced. Apoptotic signalling was suppressed. Inflammation had quietened. The cells had learned something.
That is the finding at the heart of a 2025 study published in Advanced Biology, the first human research to directly measure how cold water immersion changes autophagic function over time. It is being reported widely as evidence that cold plunging triggers cellular cleanup. And it does, eventually. But the more interesting story is about what happens before the benefit arrives, and what that early dysfunction reveals about how cold exposure and autophagy actually relate.
What autophagy does, and what happens when it fails
Autophagy is, at its simplest, a quality-control system. Every cell accumulates waste: misfolded proteins, damaged mitochondria, fragments of membrane that no longer serve a purpose. Left alone, this debris builds up. Cells become sluggish, then dysfunctional, then vulnerable to the cascading failures that characterise ageing and disease.
To deal with this debris, the cell wraps damaged material in a double-membraned structure called an autophagosome and delivers it to the lysosome, a compartment filled with enzymes that break the waste down into reusable parts. Amino acids, lipids, and nucleotides re-enter the cell’s supply chain. Junk becomes raw material.
In 2016, this recycling system earned Yoshinori Ohsumi the Nobel Prize in Physiology or Medicine. When autophagy works well, cells stay cleaner, more efficient, and more resistant to stress. When it declines, as it does with age and with chronic metabolic dysfunction, the consequences ripple outward: neurodegeneration, cardiovascular disease, cancer, accelerated ageing.
Most people encounter autophagy through fasting research, where extended food restriction activates the pathway powerfully. But the King and Kenny study is the first controlled human evidence that repeated cold water immersion can do it too, and the way it does it is more complicated than fasting’s relatively clean on-switch.
The study: ten men, seven days, and a reversal
Kelli King, whose doctoral research at the University of Ottawa focused on autophagy and cold water immersion, led the study alongside Glen Kenny, a professor of physiology at the same institution with more than 500 publications in human environmental physiology. The protocol was straightforward. Ten healthy young men immersed themselves in 14°C water for 60 minutes each day over seven consecutive days. Blood samples were taken before and after immersion on Day 1 and Day 7, then analysed for markers related to autophagy, apoptosis, and inflammation.
On Day 1, the results were striking for being precisely wrong. Markers of healthy autophagic function (LC3-II, beclin-2, phosphorylated ULK1) moved toward impairment. Meanwhile, cleaved caspase-3, a hallmark of apoptotic cell death, increased. So did inflammatory signalling. Rather than triggering cleanup, the cold had triggered damage.
By Day 7, every one of those trajectories had changed. Autophagic markers were significantly elevated above baseline. Apoptotic signalling had been suppressed. Inflammatory responses were muted. By the seventh day, the same stimulus that had produced dysfunction was producing enhanced cellular maintenance.
King’s conclusion was measured but clear: cold water immersion may represent a viable non-pharmacological approach to improving autophagic function, but only through acclimation, not through a single exposure. Your body does not give this benefit away on the first session. It builds the capacity through repetition, and the cost of building it is the initial stress that drives so many beginners to quit.
Why the first day goes wrong
The pattern makes biological sense. A sudden temperature drop triggers a cascade of survival responses: peripheral vasoconstriction, sympathetic activation, elevated cortisol, increased metabolic demand. Under acute stress, cells prioritise survival over housekeeping. Apoptotic pathways activate because the body is prepared to sacrifice damaged cells rather than invest energy in repairing them. Autophagy, which requires energy and enzymatic resources, gets deprioritised. The cellular environment looks worse because the body is making rational triage decisions under conditions it hasn’t yet learned to manage.
Repeated exposure changes the equation. The sympathetic response dampens, cortisol spikes moderate, and the body becomes more efficient at managing the thermal challenge, freeing resources for the maintenance processes that were suppressed during the initial crisis. This fits within the framework of hormesis, the principle that moderate, repeated stress triggers adaptive responses leaving the organism stronger than before, as outlined in a 2025 review in Life Sciences. Stress must be enough to provoke a response, not so much that it overwhelms recovery. And it has to recur.
Animal research supports the mechanism from a different angle. A 2021 study in iScience found that chronic cold exposure in mice stimulated autophagy specifically in brown adipose tissue, and that mice lacking the relevant autophagy gene could not maintain body temperature during cold exposure. Autophagy wasn’t just correlated with cold adaptation — it was required for it.
What the study does not prove
The study involved ten participants. All were young men. There was no control group, no cohort immersing in thermoneutral water to isolate whether the changes were caused by cold specifically or by some other aspect of repeated daily immersion. The blood markers measured are indirect indicators of autophagic activity in circulating immune cells; they do not tell us what is happening inside muscle tissue, brown fat, the brain, or any specific organ.
A predecessor study by the same team adds another complication. When older adults were subjected to similar cold stress, they showed minimal autophagic activation at either moderate or high levels. The cellular recycling response that looked so promising in young men may not generalise to the population most interested in longevity benefits.
These are not reasons to dismiss the research. It is the first controlled human evidence that cold water acclimation can enhance autophagic function, and that is genuinely significant. But it is a single study with a small, homogeneous sample. It opens a door; it does not furnish the room.
Beyond the study’s own limitations, there is a broader question about whether autophagy is even the right pathway to focus on. A 2023 study in Nature Aging found that cold temperatures extended lifespan in C. elegans through proteasome activation, a different protein-degradation pathway entirely. Cold appears to engage multiple maintenance systems, and reducing the story to autophagy alone would be an oversimplification that the current evidence does not support.
And then there is the protocol problem.
The 60-minute problem
Sixty minutes at 14°C is an enormous cold dose. Sixty minutes exceeds almost any cold water immersion protocol used in practice, clinical research, or athletic recovery. The temperature is mild by ice bath standards, but the cumulative thermal load of a full hour bears little resemblance to a short, sharp plunge.
That gap between protocol and practice is the central practical question the study raises. Across more than 500 installations, Icebaths.com observes that hospitality clients typically report sessions of two to five minutes, with units running at 6–8°C. Consumer units often operate colder still, between 3°C and 7°C. Temperatures run far lower than the study used, but durations are a fraction of it.
Does a three-minute immersion at 5°C produce the same autophagic signalling as a 60-minute soak at 14°C? Nobody knows. The total thermal load differs. The shivering response, which one recent research review argues may be necessary to activate deeper repair pathways, behaves differently across temperatures and durations. Shorter, colder sessions may trigger similar hormetic signalling: the sympathetic activation, the metabolic demand, and the cortisol response all occur in brief plunges too. But plausibility is not evidence. We are extrapolating from a protocol that nobody follows to a practice that millions of people do, and the translation remains unvalidated.
What we can say with more confidence is that the study’s structural finding, that repetition matters more than a single session, aligns with patterns visible outside the laboratory. Most users who discontinue cold water practice do so within the first month. Those who persist past three months overwhelmingly become committed, long-term practitioners. That is not proof that the same cellular mechanism is at work, but the echo is striking: the body’s relationship with cold, whether measured in blood markers or in behavioural persistence, follows a curve of initial resistance followed by adaptation.
What this means for practice
The temptation with a study like this is to derive a protocol: how cold, how long, how often to “maximise autophagy.” That would be premature. What the research actually supports is a framework: cold water immersion is a stressor the body learns to use productively through consistent, repeated exposure. The benefit is not in the first plunge but in the practice of returning while your physiology adjusts.
Kenny’s emphasis on cold water immersion as a potential non-pharmacological intervention rests on the word intervention: something done regularly, deliberately, over time. The research makes a stronger case for a cold plunge you use four times a week than for one dramatic session a month. Whether that access is a home unit at 5°C or a hotel wellness space at 8°C, the principle holds: consistency of access matters more than any single variable of temperature or duration.
If there is a protocol insight in the data, it is this: show up consistently, tolerate the early discomfort without expecting immediate cellular rewards, and give your body the time it needs to shift from crisis management to adaptive maintenance.
The adaptation, not the hack
The most important finding in the King and Kenny research is not that cold water immersion enhances autophagy. That enhancement is earned. Your body resists first, adapts second, and benefits third — and only if you keep showing up through the resistance phase. Cold exposure is not typically sold this way; the framing centres on immediate transformation. But the autophagy data tells a quieter story.
Whether or not the precise markers measured in ten young men translate to your morning routine, the principle beneath them is among the most robust in human physiology. Repeated, manageable stress, applied consistently, recovered from fully, builds capacity that a single heroic effort never will. Not a hack. An adaptation. And adaptation, by definition, takes time.
