Cold water and hormones: a one-hour lab experiment
Ten young, fit men spent an hour in water at three temperatures while researchers measured stress hormones. The coldest water produced a sharp hormone response, but this was a controlled lab test, not a quick plunge.
The short version
Ten young, fit men were immersed up to the neck in water at 32°C, 20°C and 14°C for one hour each, a week apart, while researchers measured hormones, heart rate and blood pressure. At 14°C, noradrenaline rose by roughly 530% and dopamine by roughly 250%, while metabolic rate rose by about 350%; adrenaline did not change, and cortisol tended to fall. Warmer water mainly changed blood pressure, heart rate and urine output. This was a controlled, one-hour laboratory protocol in ten fit young men, not a short cold plunge, and it cannot tell us what a brief dip does.
Keep in mind
Ten fit young men, one hour per temperature, in a laboratory. This is not what a quick cold plunge or a cool-down dip after a sauna looks like, and the numbers should not be read as a routine to copy.
What they found
At the warmest water temperature (32°C), the men’s heart rate and blood pressure fell compared with normal room-temperature conditions, along with several fluid-balance hormones, while urination increased. Rectal temperature and metabolic rate did not change.
At 14°C, metabolic rate rose by about 350%, and noradrenaline and dopamine rose by roughly 530% and 250%. Adrenaline did not change, and cortisol tended to fall rather than rise. Heart rate and blood pressure rose slightly, and urination increased even more than at 32°C.
The researchers concluded that the effects of thermoneutral or warm water are driven mainly by hormones tied to blood volume and fluid balance, while the effects of cold water are driven mainly by the body’s fight-or-flight (sympathetic nervous) response.
What this means for your practice
This study is a useful, specific data point on what happens to stress hormones during one full hour in cold water. It is not a description of an ordinary cold plunge or a brief dip after a sauna, both of which are far shorter.
Extended cold-water exposure like this carries real physiological strain, including a sharp rise in metabolic rate and stress hormones; this is not a reason to see cold water as risk-free, and it does not establish a routine to follow.
Methods and limitations
What the researchers did
Ten healthy young men (mean age about 22) each sat in a chair, immersed up to the neck in water, for one full hour at each of three temperatures (32°C, 20°C and 14°C), with the three sessions a week apart in random order.
Researchers measured rectal temperature, heart rate, blood pressure, metabolic rate and blood levels of stress hormones (noradrenaline, adrenaline, dopamine and cortisol) and other hormones involved in fluid balance, taking blood samples before immersion, during it, right after the hour ended, and again after an hour of recovery.
This is a small laboratory experiment, not a review of other research: it tells us about these ten men, in this specific protocol, rather than about cold water immersion in general.
How much can this tell us?
Ten participants is a small number for drawing firm general conclusions, and all were young, fit men, so the results may not apply the same way to women, older adults, or people who are less fit.
The one-hour, head-out, seated protocol is far longer and more controlled than a typical brief cold plunge, so the size of these percentage changes should not be assumed for a two- or three-minute dip.
This is one small experiment on hormone and cardiovascular responses. It says nothing about muscle soreness, exercise recovery, mood or longer-term health effects of cold water exposure.
What makes it useful
- Directly compared three water temperatures in the same ten men
- Careful, repeated hormone and cardiovascular measurements
- A clear, controlled laboratory protocol
What limits it
- Only ten participants, all young, fit men
- A one-hour protocol, far longer than a typical cold dip
- No comparison to shorter or more typical cold-water routines
- From the year 2000; not a recent replication
Where this study fits
Where this study fits
We score claims, not single studies. This one is part of the evidence for:
Sudden cold water puts real strain on the body. Well supported
High certaintyLarge effectIllness and death
Cold water triggers a surge of noradrenaline and dopamine. Well supported
Moderate certaintyLarge effectBody signals
Read the original
Šrámek P, Šimečková M, Janský L, Šavlíková J, Vybíral S. Human physiological responses to immersion into water of different temperatures. Eur J Appl Physiol. 2000;81(5):436-442.
DOI 10.1007/s004210050065 · PubMed 10751106