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Is it true that men and women respond differently to cold water immersion? Wisdom Wednesdays. · Hardiness with Dr Paul Taylor

• 0:05
  Speaker 1: Here everyone, Welcome to another edition of Wisdom Wednesdays. You're
• 0:09
  Speaker 1: probably a word at this stage that I'm a big
• 0:11
  Speaker 1: fan of cold water exposure, and when I'm doing workshops,
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  Speaker 1: it turns out lately I've been asked quite a lot
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  Speaker 1: by women who said that they've heard that women shouldn't
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  Speaker 1: do cold water exposure, especially perimenopausal and postmenopausal women, because
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  Speaker 1: it spikes cortisol more in man, sorry, in women than men.
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  Speaker 1: And it appears that this message comes from doctor Stacey Simms.
• 0:38
  Speaker 1: She is a researcher who I've interviewed on my podcast
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  Speaker 1: and she is awesome, and she's got a very strong
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  Speaker 1: message that lands. Her message is that women are not
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  Speaker 1: small men, and that is absolutely true. Female physiology matters.
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  Speaker 1: Hormones matters, menstrual cycle, perimenopause, menopause.
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  Speaker 2: They all matter.
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  Speaker 1: Men actually, when you look at the research, have traditionally
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  Speaker 1: been very underrepresented in some scientific studies. In fact, quite
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  Speaker 1: a lot of scientific studies precisely for those reasons, because
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  Speaker 1: researchers need to control as many variables as they can,
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  Speaker 1: and menstrual cycles tend to screw up quite a lot
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  Speaker 1: of variables, so they are underrepresented in research and it
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  Speaker 1: turns out that there are clear differences in how women
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  Speaker 1: and men metabolize certain drugs. If you think of sleeping tablets,
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  Speaker 1: women metabolize them a lot slower. The research was done
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  Speaker 1: on men, and it turns out that women tend to
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  Speaker 1: be groggy in the next day if they take sleeping tablets,
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  Speaker 1: particularly in the same doses as men. We also know
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  Speaker 1: a lot of the fasting research was done initially on
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  Speaker 1: men and then on women. When they did fasting research,
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  Speaker 1: it turns out that they didn't respond on average and
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  Speaker 1: the way that men do. But it doesn't mean because
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  Speaker 1: of that that men and women respond differently to everything,
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  Speaker 1: and it doesn't mean that every claim about women in
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  Speaker 1: cold exposure is automatically true. So today I want to
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  Speaker 1: actually wanted to do a deep dive and say what
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  Speaker 1: does this science actually say about whether there are any
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  Speaker 1: sex differences in cold exposure. And so I've looked at
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  Speaker 1: a huge amount of studies on this, and the first
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  Speaker 1: one I think we need to start at the start
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  Speaker 1: because there's the classic study and the title of the
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  Speaker 1: study is Human physiology responses to immersion in water of
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  Speaker 1: different temperatures.
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  Speaker 2: This was by Schramac and colleagues.
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  Speaker 1: And was published way back in two thousand in the
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  Speaker 1: European Journal of Applied Physiology. And what they did in
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  Speaker 1: this classic study was a study of young men right,
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  Speaker 1: and they were immersed in water at different temperatures including
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  Speaker 1: fourteen degrees celsius, and the researchers measure things like metabolic reate,
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  Speaker 1: heart rate, rectal temperature. They then measured things like noradge, drenaline,
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  Speaker 1: adrenaline with our American friends called epidephrin nor epinephrin, but
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  Speaker 1: also dopamine, aldosterone, renin, and cortisol. So they did a
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  Speaker 1: very very comprehensive measurement protocol and this works get interesting.
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  Speaker 1: So at fourteen degree celsius, this is nor adrenaline or
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  Speaker 1: nor epinephrine increased by around five hundred and thirty percent
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  Speaker 1: and then dopamine increased by around two hundred and fifty percent.
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  Speaker 1: And so what was clear from this is that cold
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  Speaker 1: water is absolutely a stimulus to the sympathetic nervous system.
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  Speaker 1: But cortisol it didn't increase at all, It tended to decrease.
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  Speaker 1: Nine just a quick double top on looking at stress responses.
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  Speaker 2: So your sympathetic.
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  Speaker 1: Nervous system that involves stress homage adrenaline no adrenaline, which we.
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  Speaker 2: Saw rise in this study. And then we have another.
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  Speaker 1: Part part of our stress response system called the HPA
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  Speaker 1: axis hypothalamus, proturatory grand and the adrenal gland, and that
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  Speaker 1: releases stress hormones such as cortisol colors also the major.
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  Speaker 2: One in humans.
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  Speaker 1: So it's a different part of our stress response. And
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  Speaker 1: then when you look in the classic studies around exercise,
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  Speaker 1: you see that exercise will spike.
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  Speaker 2: You're adrenaline and your no adrenaline.
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  Speaker 1: But doesn't spike cortisol until later on, until we get
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  Speaker 1: into endurance exercise and you start to run out of
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  Speaker 1: blood glucox. But anyway, if we come back to this,
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  Speaker 1: one of the most cited studies in this field showed
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  Speaker 1: a strong nor adrenaline and doperine response, but not a
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  Speaker 1: cortisol spike, actually a reduction in cortisol.
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  Speaker 2: But that was in Man.
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  Speaker 1: So now let's look at a gender specific stuff. There
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  Speaker 1: was a great paper called gender specific cold Responses induced
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  Speaker 1: a similar body cooling rate but different neuroendocrin and immune responses.
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  Speaker 1: Now this is Bysolianic and colleagues, and it was published
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  Speaker 1: in twenty fourteen in the journal Cryobiology, and they had
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  Speaker 1: thirty two participants in the study.
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  Speaker 2: Eighteen were men and fourteen were.
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  Speaker 1: Women, and they were immersed up to the upper chest
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  Speaker 1: level in fourteen degree water.
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  Speaker 2: So this is not a thirty second cold shower. This
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  Speaker 2: is pretty serious cold exposure.
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  Speaker 1: And they were in there and it was really about
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  Speaker 1: an outcome until their rectal temperature drops, so core body
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  Speaker 1: temperature dropped to thirty five point five degrees centigrade or
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  Speaker 1: a maximum of one hundred and seventy minutes. So this
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  Speaker 1: is pretty significant. I don't know if anybody's been in
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  Speaker 1: fourteen degree cold water.
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  Speaker 2: It's pretty chilly. Be it in there for over two hours,
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  Speaker 2: you know all about it.
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  Speaker 1: And now the researchers looked at body cooling, they looked
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  Speaker 1: at thermal regulation, they looked at immune markers and neuroendocrime responses,
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  Speaker 1: and what do they find. They found that men and
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  Speaker 1: women could at a similar rate, but they used different strategies.
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  Speaker 1: The women showed more insulation and heat conservation and the
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  Speaker 1: men showed more metabolic heat production, more active heat generation
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  Speaker 1: in order to try and maintain their core body temperature.
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  Speaker 1: So yes, there are sex differences in how we respond
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  Speaker 1: but this study did not support the claim that women
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  Speaker 1: have a uniquely dangerous spike cortisol spike from cold water.
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  Speaker 1: If anything, it shows that men and women can respond differently,
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  Speaker 1: but not in the simplistic way that social media and
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  Speaker 1: influencers often represent it. Now there's a third study, and
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  Speaker 1: this is important because it did find cortisol increases. And
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  Speaker 1: the name of the study was residual effects of short
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  Speaker 1: term whole body cold water immersion on the side of
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  Speaker 1: kine profile, white blood cell car and blood markers of stress.
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  Speaker 1: And this was published in twenty twenty one in the
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  Speaker 1: International Journal of Hyperthermia. And this study involved twelve young men.
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  Speaker 1: They were immersed in fourteen degree water for ten minutes.
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  Speaker 1: The researchers metic breathing, shivering, metabolic heat production, heart rate,
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  Speaker 1: immune markers, no adrenaline, adrenaline.
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  Speaker 2: And cortisol.
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  Speaker 1: And here they find slight increases in cortisol, but bigger
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  Speaker 1: increases in adrenaline and now adrenaline, So cortisol didly increase here. Now,
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  Speaker 1: unfortunately this was just men, but the dose matters. Now,
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  Speaker 1: this was not a thirty second coal shoar. This was
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  Speaker 1: ten minutes of whole body right up to the neck
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  Speaker 1: cold water immersion at fourteen degrees. So if someone says
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  Speaker 1: cold water can increase your cortisol, yes it can, but
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  Speaker 1: under some conditions. But if they make the jump and
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  Speaker 1: say therefore women should avoid cold exposure, and this study
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  Speaker 1: and the other ones that I've talked about so far
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  Speaker 1: does not show that.
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  Speaker 2: Right. Again, this study was only a man.
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  Speaker 1: Let's look at a more recent ice bath study and
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  Speaker 1: the RATS research paper's effects of time of Day on
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  Speaker 1: NOH adrenaline, adrenaline, cortisol, and plasma lipidome responses to an
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  Speaker 1: ice bath, and this was published in twenty twenty five
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  Speaker 1: in the journal Scientific Reports. Now, this was a crossover
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  Speaker 1: study with twelve participants, six women and six men. Their
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  Speaker 1: average age was twenty six, and they did a five
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  Speaker 1: minute ice path at eight.
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  Speaker 2: To twelve degrees celsius.
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  Speaker 1: This is getting like if you go from fourteen to eight,
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  Speaker 1: that's really quite significant.
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  Speaker 2: Now.
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  Speaker 1: They did this once in the morning and once in
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  Speaker 1: the evening, and the researchers measured NORA adrenaline as I
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  Speaker 1: talked about the measure of adrenaline, they also measured cortisol
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  Speaker 1: and their blood lipids before five minutes after and thirty
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  Speaker 1: minutes after the ice bath exposure.
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  Speaker 2: What happened.
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  Speaker 1: Adrenaline increased significantly after the ice bath, about one hundred
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  Speaker 1: and twenty seven percent in the morning and one hundred
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  Speaker 1: and forty four percent in the evening. Adrenaline did not
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  Speaker 1: significantly change. Cortisol did not significantly change because of the
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  Speaker 1: ice bath. Now, cortisols tend to be higher in the
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  Speaker 1: morning than the evening, but that is normal circadian biology.
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  Speaker 1: Cortisol is usually higher in the morning anyway, unless your
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  Speaker 1: cordisol rhythm is completely screwed up. Importantly, they find no
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  Speaker 1: meaningful difference between men and women in the hormonal response. Now,
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  Speaker 1: this is a small study, but it was both women
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  Speaker 1: and men, and it was exposure to pretty cold temperatures
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  Speaker 1: for five minutes.
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  Speaker 2: But it directly challenges.
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  Speaker 1: The idea that a short ice path automatically courses a
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  Speaker 1: cordisol spike, especially in women. And look, this is the
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  Speaker 1: most recent of the studies that I've talked about, and
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  Speaker 1: generally we get better as we go in terms of
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  Speaker 1: the the whole study design.
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  Speaker 2: And then there's another useful.
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  Speaker 1: Study and the title of that is short term head
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  Speaker 1: out whole body cold water immersion facilitates positive affect and
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  Speaker 1: increases interaction between large scale Brian networks. And now this
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  Speaker 1: was published in twenty twenty three in a General Biology
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  Speaker 1: and it had thirty three healthy adults at booth men
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  Speaker 1: and women. They set in twenty degree water for five
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  Speaker 1: minutes immersed up to the chest, so not as cold.
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  Speaker 2: Twenty degrees is very very different.
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  Speaker 1: Now, they weren't measuring cords all here, but what they
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  Speaker 1: were looking at were mood and breen and connect mood
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  Speaker 1: changes in brain connectivity using functional MRI. After the cold
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  Speaker 1: water immersion, the participants on average reported feeling more active, alert, attentive,
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  Speaker 1: pride and inspired and less distressed and nervous. That is
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  Speaker 1: not a proof of hormonal benefits. But if your core
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  Speaker 1: is all is high, you are not feeling active, alert, attentive,
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  Speaker 1: pride and inspired and less destroy and less nervous. Now
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  Speaker 1: it supports This study supports the idea that cold water
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  Speaker 1: exposure can improve moon and alertness without needing extreme temperatures
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  Speaker 1: or long duration. And then we have a big picture
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  Speaker 1: paper Effects of cold water immertional on health and well being,
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  Speaker 1: a systematic review and meta analysis. This is published by
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  Speaker 1: Cane colleagues in twenty twenty five in the Journal plus one.
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  Speaker 1: They looked at eleven studies in over three thousand participants
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  Speaker 1: and included cold chars, ice.
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  Speaker 2: Baths, and clothed plunges.
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  Speaker 1: And now to be included, the water had to be
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  Speaker 1: fifteen degrees celsius or colder, and exposure had to be
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  Speaker 1: at least thirty seconds.
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  Speaker 2: The review found that cold water.
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  Speaker 1: Immersion may have time dependent effects on stress, inflammation, immunity, sleep,
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  Speaker 1: and quality of life. Right, so what that means is
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  Speaker 1: that the longest stay in it changes the effects. Now,
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  Speaker 1: the authors were pretty careful, as they are in most
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  Speaker 1: systematic reviews because there's different protocols and things like that,
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  Speaker 1: and they said the evidence is limited by small samples,
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  Speaker 1: few randomized control trials, and a lack of diversity and participants.
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  Speaker 1: In other words, and you know, the research is promising,
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  Speaker 1: but it's not definitive. Now, importantly, this review does not
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  Speaker 1: conclude that women should avoid cold exposure, because of.
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  Speaker 2: Course all spikes.
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  Speaker 1: So when you look at this in totality, and I've
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  Speaker 1: scared quite a lot of journal articles, the ones that
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  Speaker 1: I could find on it, we find that cold water.
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  Speaker 2: Exposure is a stressor.
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  Speaker 1: It's a hormetic stressor you've heard me talk about hormesis.
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  Speaker 1: That is the science of sublethal exposure to stressors or
• 12:42
  Speaker 1: toxins which at high levels can kill you, but at
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  Speaker 1: low to moderate levels induce stress resistance. Exercises a hormetic stressor.
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  Speaker 1: Sauna is a hormetic stressor fasting is a hermetic stressor
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  Speaker 1: learning hard things is a hermetic stressor cold exposure is
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  Speaker 1: a hermetic stressor.
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  Speaker 2: So the question is not does this stress the body?
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  Speaker 1: The better question is what is the dose and can
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  Speaker 1: the person recover and adapt? And the most consistent finding
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  Speaker 1: across the cold water literature is not a significant spike
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  Speaker 1: in cortisol. The most consistent finding is sympathetic nervous system activation.
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  Speaker 1: And the biggest spike that we find is in nora adrenaline.
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  Speaker 1: Right now, that is a stress hormone, but it's a
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  Speaker 1: different stress hormone to cortisol. It's part of the sympathetic
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  Speaker 1: nervous system, not the heatpi access. Adrenaline means increased alertness, focus,
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  Speaker 1: vasal constriction, cold shock response, increase breathing and in some
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  Speaker 1: cases shivering and heat production. Now cords all may well
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  Speaker 1: rise when the exposure is long enough intense enough, are
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  Speaker 1: psychologically stressful enough. But the evidence does not support the
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  Speaker 1: blanket statement that women should avoid code exposure. And the
• 13:55
  Speaker 1: evidence clearly does not support the idea that a thirty
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  Speaker 1: second code is some endogrink catastrophe. Now, when I interviewed
• 14:04
  Speaker 1: Professor Mike Tipton on my podcast, he's at Portsmouth University.
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  Speaker 1: He is the guy I considered be the world leader
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  Speaker 1: in cold water exposure.
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  Speaker 2: He'd been doing this long before anybody else.
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  Speaker 1: And Mike said to me that the biggest amount of
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  Speaker 1: benefits come from the first minute of cold exposure. And
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  Speaker 1: he said anything under about fifteen degrees cent degree induces
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  Speaker 1: the cold water shock response, and twenty degrees if you're
• 14:33
  Speaker 1: staying in a bit longer, you get the cold water
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  Speaker 1: shock response. But it is really about that early, short
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  Speaker 1: time exposure. So my take is this, and having listened
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  Speaker 1: to Mike and read all of these research paper, cold
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  Speaker 1: water exposure is absolutely fine for most healthy people. The
• 14:51
  Speaker 1: people that you've got to be aware of the people
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  Speaker 1: who've had recent cardiac problems.
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  Speaker 2: But here's the key tweak the variables.
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  Speaker 1: Temperature does matter, and it doesn't have to be a
• 15:04
  Speaker 1: two to three or four degree cent degrade ice bath,
• 15:07
  Speaker 1: anything under fifteen degrees is critical. Time matters as well,
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  Speaker 1: So the more time you are in there, the more.
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  Speaker 2: Stress hormones you're going to produce.
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  Speaker 1: We want that short, short term quick spike in no
• 15:22
  Speaker 1: adrenaline and in dopamine. But if you stay in there
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  Speaker 1: all day, of course you're going to release cortosol. And
• 15:29
  Speaker 1: now your current stress load also matters. Your sleep matters
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  Speaker 1: as well. Your psychological relationship with the cold matters as well.
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  Speaker 1: Now forget this whole stuff that you see on Instagram
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  Speaker 1: about people doing eight minute ice baths or ten minute
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  Speaker 1: ice baths and stuff like that.
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  Speaker 2: That for me is just ego, and.
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  Speaker 1: For many people, thirty seconds in an ice bath will
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  Speaker 1: be absolutely plenty. Or two to five minutes in water
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  Speaker 1: fifteen degrees are yes, that is enough to get a
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  Speaker 1: heap of the benefits, in fact, probably most of the benefits.
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  Speaker 1: And even a short cold shar turning that lovely warm
• 16:10
  Speaker 1: short of cold for thirty seconds is a brilliant way
• 16:15
  Speaker 1: to practice nervous system regulation. Build tolerant to distolerance to
• 16:19
  Speaker 1: discomfort and get that no adrenaline and dopa being driven,
• 16:24
  Speaker 1: lift in alertness and the motivation and Honestly, the only
• 16:30
  Speaker 1: way that a thirty second cold shar is going to
• 16:32
  Speaker 1: spike your core asol is if you spend twenty minutes
• 16:36
  Speaker 1: beforehand stressing about unscientific soundback from social media influencers. So yes,
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  Speaker 1: women are not small men. But there's a more important
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  Speaker 1: point here. Not all women respond the same and not
• 16:48
  Speaker 1: all men respond the same.
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  Speaker 2: With any scientific study, there tend to be.
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  Speaker 1: Responders, non responders, and often hyper responders. There is no
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  Speaker 1: one side fits all in science, whether that's drug responses,
• 17:03
  Speaker 1: datary responses, training, fasting, or cold water responses. But women
• 17:07
  Speaker 1: are not fragile flowers who need to be scurred away
• 17:10
  Speaker 1: from every hormetic stressor. The science is to individualize it,
• 17:15
  Speaker 1: and I would suggest that you start short and don't
• 17:19
  Speaker 1: go too cold, don't chase suffering, adjust the dose, adjust
• 17:23
  Speaker 1: the temperature, and remember cold exposures should make you feel
• 17:27
  Speaker 1: better afterwards, not wrecked. That is what the sweet spot is.
• 17:31
  Speaker 1: So be your own scientist, run your own experiment and
• 17:34
  Speaker 1: see how you respond. By a word to the wise,
• 17:37
  Speaker 1: when running your experiment on hormetic stressors such as exercise, diet, fasting,
• 17:42
  Speaker 1: and cold exposure, be careful not to confuse your mind
• 17:46
  Speaker 1: telling you I don't like this because it feels a
• 17:49
  Speaker 1: bit uncomfortable with I'm not going to do this because
• 17:53
  Speaker 1: my physiology rejacts differently to most people. So go and
• 17:57
  Speaker 1: turn your lovely warmshow to cold for thirty seconds at
• 18:00
  Speaker 1: the end, and then take it from there.
• 18:02
  Speaker 2: Catch you next time.