The Transformative Power of Winter Swimming: Unveiling the Benefits of Cold Exposure

Researcher Susanna Søberg explains the physiology behind winter swimming — brown fat, dopamine, the ctrl-delete effect — and the precise protocols that make cold exposure genuinely transformative.

Researcher Susanna Søberg explains why winter swimming is more than a wellness trend — and how even thirty seconds of cold water can shift your brain chemistry.

Cold Water as a Complete Practice

The name matters. Winter swimming is not cold plunging rebranded — it is a complete concept, the full act of submerging into nature, of entering something elemental, of belonging to a world beyond temperature-controlled rooms. The ritual begins before you reach the water and continues long after you leave it. This distinction is not semantic; it shapes the entire practice.

Susanna Søberg approached winter swimming as a neutral scientist. She entered her research without a personal stake in cold exposure, genuinely uncertain whether the practice was beneficial or harmful. Her investigation was methodical and open: she wanted to know what the evidence said, not confirm what she already believed. What she found settled the question — and the answer gave rise to one of the most grounded bodies of research on cold as a tool for human health and longevity.

I didn't want to go out and prove something. I was just a scientist trying to figure out whether cold or heat could activate our metabolism.

When you step into cold water, your sympathetic nervous system activates immediately. Heart rate rises. Metabolic rate climbs. Your body shifts into a state of heightened alertness and energy mobilization — not alarm, but precision. The system is doing exactly what it was designed to do: prepare you to meet a challenge with full capacity.

What fuels that response is brown fat. Unlike white fat, which stores energy as a long-term reserve, brown fat burns it — drawing glucose and lipids from the bloodstream to generate heat and hold core temperature at the level your vital organs require. Cold water forces this engine to work, and that work is real. The cells responsible for this thermal effort continue adapting even after you exit the water, preparing for the next exposure.

The principle underlying all of this is hormesis. Brief, controlled cold exposure creates a small, intentional stress in the body — and the body responds by rebuilding stronger. Cells repair; mitochondria multiply in muscle fibers and brown fat tissue, increasing both heat-generating capacity and metabolic resilience. This is the same adaptive cycle that makes exercise transformative, applied through temperature rather than load.

This adaptation is not passive. The body does not simply tolerate cold water over time; it actively reorganizes itself in response to each exposure. Mitochondrial density increases. The vascular system becomes more responsive. Each session adds to a cumulative architecture of resilience that expresses itself in energy, focus, and recovery.

The cultural dimension of winter swimming is not ornamental. When Søberg chose to title her book "Winter Swimming" rather than something more clinical, she was making a deliberate statement about what the practice actually is. A cold plunge tub delivers cold. Winter swimming delivers cold, nature, community, and the particular stillness that comes from being present in an environment that demands your full attention. You access some of the benefits when you enter a tub; you access the full concept when you enter the world.

View transcript

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listen I love your book and one of the things that  I love yeah one of the things that I love the most   about this book Winter Swimming is that you didn't  entitle it you didn't call it the science of cold   plunging or you didn't call it uh the benefits  of ice bathing or something like that you call   it winter swimming which conveys this idea of  connecting to nature um would you say that winter   swimming in a natural body of water is like the  gold standard of cold plunging of cold exposure   i would say this is where it really originates  and uh thank you for the compliment on the title   of the book because I really think that you with  that address something that nobody else I don't   think people really notice it but winter swimming  doesn't need anything else it's kind of where   everything originated with this whole trend and  now I'm doing the science and cold exposure but  

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really what we actually did go into is the concept  of winter swimming what is it and this book is   not only about the science it's also about the  feeling what do you get out of this this is this   is a cultural thing right so it's also something  embodied so you really go out into the nature and   you submerge into nature so winter swimming is  more the whole concept of it it's not only the   science and that's why it's only called winter  swimming so you get some of these benefits when   you plunge into a an a top or some a co-plunch but  you don't get the whole concept of submerging into   nature so that's why it's called winter swimming  that's that's the idea I got from it that's why   it really caught my attention um and I love it um  how did you first um got into cold and what's the   story behind this book supervisor was asked  can you write a book about this and she said   well I cannot write a book about it but I know  someone who can and she asked me very politely do  

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you want to write a book about it and I was like  actually no I was not I was not sure whether this   is going to be a book which is about why winter  swimming is unhealthy for you or healthy for you   so at this stage I actually didn't know and I was  not a winter swimmer so I didn't have I was not   biased in that sense i didn't want to go out and  prove something i didn't really care i was just   a scientist trying to figure out whether cold or  heat or whatever could activate our metabolism and   then I dived into the research to figure out is  winter swimming or cold exposure actually healthy   or unhealthy for us and that became the working  title of the book that you just read which is   called winter swimming so that's why the safety  is actually in there as well because I researched   whether it's actually dangerous or is it actually  healthy so it's both the size you you you kind of   need to know right so I wanted to tell people  that but eventually I said yes and obviously  

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the conclusion is that yes it is beneficial for  our health maybe we can start with the very very   basics which are the physiological benefits  of winter swimming uh the the physiological   benefits of winter swimming um are multiple so you  can say there's the metabolic benefits which is   uh when you submerge it in cold water you will  have this activation of your sympathetic nervous   system right so you will have an increase in  heart rate you have increase in your metabolic   rate and for those people are thinking what is  the metabolic rate even that is when you burn   your fat and your sugar from your bloodstream  because you have cells in your body which are   trying to keep you warm and for that it needs  fuel just like an engine right so these cells   in the body takes glucose and it takes so that  is sugar and fat from the bloodstream as fuel to   activate heat in the body and the tissue which is  doing that is something called the brown fat and  

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the brown fat is keeping your temperature in  your body at the perfect temperature balance   so you won't get too warm or too cold and that  takes energy from the body so that's why when   going out in extreme temperatures you can actually  activate that engine uh making sure that you have   the perfect temperature for your vital organs and  that burns calories just like going to the gym so   and it's all it's not only when you are in the  water it actually works the the cells afterwards   are trying to um adapt to this situation so when  you next time you do it it's already prepared for   it right it's just like when you go to the gym  you you use your muscles when the muscles are   break broken down a little bit it makes it so  stronger um with this inflammatory condition   because it tries to like rebuild itself um and  that's why it hurts in your muscles when you have   done a workout and the same is when you go out in  the cold water or you actually also go into the   sauna you will create that hormetic stress the  healthy stress in the cells which create this  

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adaptation makes it stronger for the next time so  that's why the metabolism is definitely activated   when you go out in the cold water so that's only  the metabolism part but there are more of course   and beyond these um physiological benefits it's  clear that for anybody who has done a little bit   of cold exposure exposure winter swimming that  this has a an obvious and non-negligible positive   effect on mood this like this boosting in our  mood after that um what's the reason behind it   why is this happening yeah it's so This benefit  that you get out of going into the water and the   metab the metabolism side of it is of course not  something that you feel right away but what you   do feel is the mood you have a change in your mood  immediately i always say that it's impossible to  

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go out in the cold water and have the same state  of mind when you go out again it's impossible   because you just change your brain chemistry  when you change your brain chemistry like that   to the more positive side you also view whatever  you are thinking about whatever you are worried   about in a different way when you go out again  and I think that is so this this is so important   so if you're not going for the long-term benefits  of your metabolism or your your immune system or   whatever you just want to have a shift in your  mood then take a cold shower or you could go   out in the cold water do a cold plunge because it  really t I called this the control delete effect   and I think it's in the book even um or maybe  it's my new book but it's in some book I wrote i I've seen so many uh interviews and I've read  so many things uh to prepare for this that I   don't know where I've read what I've read you  know uh we have we have um seen an a lot of uh  

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social media posts on like people ice bathing and  people going into nature and winter swimming and   all this and it's great but I was thinking that  um even though this is awesome and and like I I   do it and a lot of people uh do it will you do it  i'm sorry yeah you you do it yourself oh yeah yeah   I've been doing that for a long time even before  I I knew about all this yeah like uh swimming in   the ocean in the winter it's like an old practice  where I live a lot of people do it fantastic yeah   yeah um but now I understand better why it has  these benefits that it has you know yeah but   my my question is for those people who maybe are  not inclined to go and get into the ocean water in   January or getting into an ice bath what is the  minimum effective dose of getting um of getting   into the cold meaning is there a practice that  being softer can give us like 80% of the benefits  

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without having to do the whole logistics of  filling the bathtub with uh with ice or going in   people that don't have access to a beach or a lake  or a river so is there like a minimum effective   dose that we can um practice every day to get  most of the benefits yeah so I would say a cold   shower is accessible to most people um ending your  your hot shower on a cold uh so just turning to   the cold water for 30 seconds that could actually  give you that boost in your mood and it will also   activate your metabolism so you would get some of  the benefits it's not completely the same because   you you don't activate your full nervous system  um like you would do when you submerge into cold   water and it's a little bit technical but when  you submerge into cold water you will also have   an activation of your parasympathetic part of  your nervous system which is the the part of  

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your nervous system which is the rest system and  when you dive into the cold water not dive but   submerge your body into it you will activate  your diving reflex so you don't completely do   that with the cold shower but you will get some of  the benefits from activating the fight and flight   system of your uh nervous system and some people  are like "Oh but that's that's stress and that's   not good." But that's kind of like a one of the  misconceptions I think there's out there people   being too afraid of being stressed and being  stressed is not the same as being chronically   stressed this is good stress short-term stress  30 seconds of cold shower will actually increase   these dopamine and no adrenaline in your brain  which will keep you in a good mood or get you   in a good mood give you the energy and drive to  get through the day so you can benefit from this   in your work life in your family life in in your  social life because it's also something that makes   you more um uh give you the energy to be more  approachable maybe maybe you are more you have the  

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energy to go out and talk more to people um and  some people need that extra drive to go out and   do that so the kick from the cold is definitely  something people can benefit from right away um   and it's accessible so So do I conclude correctly  if I if I if I um summarize saying that yes like a   cold shower can give you a substantial part of  the benefits but if you want the full picture   it's better to go into the water is that what it  is yeah I would say it there's definitely also   more studies on um going in submerging into cold  water compared to uh to the scientific studies   in in showers we don't have that much research  on it yet um it seems that um if you compare it   that it it's that the activates activation of the  full autonomic nervous system is there when you  

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submerge into cold water compared to when you only  do a shower so there are definitely benefits of   both and I think if you don't have a top you don't  have the ocean or lake nearby then do whatever is   ne accessible to you so yeah so okay so for those  who do want to go all the way in into the practice   tell me about tell me about how long and how  often is like the sweet spot in which we get the   benefits without harming ourselves so how often  should we do it and for how long in the water yeah   so this question is of a lot of debate apparently  h I would say most people why it's debated is   mostly because people don't know i would say there  is not a lot that long-term cold water immersion   has any health benefits for you and people it  doesn't there is no research showing that staying  

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in long-term in cold water has any benefits  health benefits for you mentally or physically   or anything so please listen you can do with  just a few minutes when you submerge into cold   water you activate your sympathetic nervous system  your parasympathetic nervous system and if you can   breathe yourself through the cold shock which  is where when you start to like hyperventilate   and your heart rate increases and then if you can  breathe through that you would decrease your heart   rate and you would get into that calm state where  you actually decrease your stress in the body and   there are studies showing that when you um when  you do cold water immersions on a regular basis   you would decrease your levels of cotisol and if  people don't really know what what is that exactly   well it's actually the stress hormone which we  want to decrease on a long-term basis do we want  

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to increase cortisol on a short-term basis right  acutely yes of course we want to do that because   that's what you do when you go to the gym also and  and some people also have a small increase when   you go into the cold water but only when you're  new to it it seems from scientific studies you   actually decrease the long-term cortisol levels  on a long term so you do want to you do want to   do that because that decreases also the risk of  lifestyle diseases we know that there is this   is correlated cortisol levels being high then you  also increase the risk of obesity type 2 diabetes   and even all mental diseases as well so you do  want to decrease that submerging into cold water   is something that people will benefit from but  shortly shortly what does that mean i'm going to   try to push you in the corner just a few minutes  just a few minutes 2 minutes 1 2 3 something like   that something like that you don't have to uh I  mean look at your watch have something that shows   you how long you stayed in the water because  suddenly when you have practiced this a few  

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times then you'll be sitting there for my maybe  8 10 minutes and it's not necessary you you must   know it's right it's like time vanishes from you  but what happens when you stay in the cold water   for that long is that you decrease the temperature  too much in your core um and it's not like it does   that immediately but when you cool your skin that  much you don't have to cool it that much actually   to activate these cold receptors that is necessary  to get the health benefits but when you stay there   for a longer time you just cool your inner organs  eventually when you get up you will have the   something called the after drop and the after drop  is cooling your inner organs so stay away from   long-term exposure even though some people think  it's a competition or they should stay longer   longer is better but it's not when it comes to  cold and heat these are extreme temperatures and   that is something that we can benefit from if we  just use it in a small dose i hope it's clear yeah  

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so people this is not a competition just a few  minutes more is not better um what about less is   more less is more less is more in this case right  uh what about uh is it is there any difference   in the effects by doing it in the morning in the  evenings i know this is very specific but people   love to know these things is it better to do it  in the morning or in the evenings is there any   difference i I I actually I love this this way  of thinking about it so when I did this research   I and when I started to become a winter swimmer  myself I had to try it out i mean they they were   all all the winter swimmers in Denmark were like  writing me hey Susanna you have to do this when   you're doing the research and I was not a winter  swimmer i was just looking standing on the jett   like observing them and being like "Wow this is  so this looks so dangerous and looks so weird   why are people so happy about this?" I started  doing winter swimming and eventually I started   out doing it in the morning which gave me all  this drive and energy and I because then I had  

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all that all day and by the afternoon I could feel  that if I if I started to do it in the afternoon   again I would just have that energy and drive in  the evening so one day I tried it out and it was   just like coffee for me coffee is something  I don't drink after 4 or 5 in the afternoon   definitely not after five because then I cannot  sleep and then I found out that it's the same   with the cold exposure and when you then look at  the literature it looks it's completely making   sense so when you go into the cold water you have  an increase in dopamine and nor adrenaline and   no adrenaline is something that gives you energy  and dopamine as well you don't want that kick uh   in the evening before you go to bed mhm what you  can do is doing your cold exposure in the morning   your cold shower in the morning but then in the  evening you should do something else you should do   the sauna do something with heat it could also be  a sauna blanket this is something you can purchase  

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online somewhere uh and these can actually help  you increase the temperature in your body and   that will make your body scream to just dump all  the heat because you want to dump the heat to fall   asleep your core temperature needs to decrease to  fall asleep so it's kind of like counterintuitive   in the evening that you want to decrease your core  temperature and then you should expose yourself   to some some kind of heat but actually it works  it does work you you sleep like a baby when you   have a sauna in the evenings you sleep like a baby  do you have a sauna yes um yeah I'm I'm like full   in the whole practice fantastic i'm falling into  the hot practice um uh something that I read in   your book also that was very interesting to me  that I didn't know is that there is a threshold   um as the water uh water temperature goes down  there is a threshold beyond which the feeling  

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of how cold the water is increases very suddenly  meaning that as the temperature of the water goes   down the perception of how cold it is it's not  linear all of a sudden at 15° you explain in the   book at 15° it really feels cold all of a sudden  and when I read it it's like yeah it's so true   like if you go to the beach and the water is at  24° and the following day is at 20° you don't feel   that much of a difference but if one day you go  and the water is like 18 and the following day is   at 14 it's the same four degrees but it feels  like another world of how much colder it is   right do do you think there is a physiological  reason or like an evolutionary reason for this   why why is that because it does like I realize  that it's true but I've been asking myself why   would that be physiologically is there a reason  for this yes i would say it's about adaptation   so when we adapt to a situation we are built  to adapt that is that is like built into our  

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DNA we were involved in in in in cold and heat  and we survived ice ages and uh heat uh waves so   our DNA is made to be able to balance that uh that  temperature um uh you can say extremes so we have   to be able to adapt so as soon as you expose your  body to some kind of danger we would try to adapt   to that situation because it might happen again  and then we want to be stronger and prepared so   we can survive so the body just prepares itself so  when you go into unit mentioned uh let's say 24° C   uh hot water I would say um the body reacts to it  as if it's like oh this is this is a nut situation   compared to the air temperature and then it adapts  to that then you go out again the next day in 20°  

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Celsius uh hot cold water something between um and  the body would be like oh I tried this before it's   a bit colder let's adapt to that and then When you  go into cold water which is 15° C the body will be   more adapted to the situation this is familiar to  the body the temperature might be colder but you   have done it before so the body gets faster and  faster at adapting to the situation because the   environmental factors is submerging into cold  water or submerging into water and you just   get adapted to that and our body is so fast at  adapting to new situations we are built to this   you're built for ad adaptation it doesn't matter  if it's if it's cold water or if it's a heat in   the sauna we are so fast at adapting to the  situation but that is also a slippery slope   right so it might be that some that shorter is  better and necessarily not colder is better you  

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don't have to go down to zero degrees some people  think that this is a dose of temperature going   down and timing going up which will be better for  you so it's a slippery slope where you at at the   end cannot really feel the code anymore because  you're so adapted to it your blood vessels are   getting so good at contracting that you don't  even feel it anymore so just keep being mindful   around what is healthy and what is not healthy h  eventually it could become something that which   has nothing to do with health so the body needs  to be reminded of the cold let's say it that way   reminded of the cold and the adaptation slowly  is super good so if you live in a country where   you are able to use the seasons then just keep  going from the summer and then you will adapt   uh to the cold water um much more lightly I  would say yeah progressively yeah so you were  

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um talking about adapt adapting to the cold to  what extent like obviously when you start doing   this for a while you get used to it and it's easy  it become it gets easier and easier and but I have   always asked myself in what proportion this is  physiological adaptation of the body and to what   extension it is a mental game so to what extension  you just you get used to suffering in a way or   you it's familiar it's a familiar feeling so you  just don't think about And to what extent is the   physiological adaptation is this 50/50 is there  what part is mental and what part is physical yeah   I like that question because I think they follow  along so one thing is in the beginning let's say   your first the first time you go into cold water  you will be anxious and that means your body will   react to that so you will have an increase in  your heart rate and that's going to affect your   breathing as well so what you think and what you  um what you're anxious about is going to affect  

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your will give some physiological uh reactions and  that will have an impact on how long you will stay   in the water or or your experience going into the  cold water but as you adapt physiologically you   will also adapt mentally so when you feel that  that oh I can recognize this situation now I've   done it maybe three times four times five times  then you will stop being so anxious about it and   then mentally you will also be more relaxed doing  it because you kind of know what you're doing now   right you've done it a few times so just just be  mindful that of course the first time is going to   be a little bit more stressful um and also maybe  second and third time but then your body will   start to recognize the situation even more and it  goes so fast the adaptation is incredible fast and   the body remembers this a whole year later there's  actually research showing this so yeah so even if   you get pregnant and you don't want to do the cold  water immersion and I don't recommend that you do  

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um just want to pop that in um yeah uh but but  as a pregnant woman just take a pause on it and   uh wait the ninth month or maybe three more and  just uh go start up again because this is this   is something that is once in a lifetime you are  pregnant and you don't want to harm your your your   baby uh you we frankly don't really know what's  happening when the little baby is in there so but   after that I would say it's mentally and it's  physically and they work together now that you   u make that comment on pregnant woman I I wanted  to ask you later about this but now that we have   opened that um box of worms let's just lean into  it um there there has been some backslash uh to   the practice lately over the past few years like  some people suggesting that well there are many   people already with compromised immune systems and  with low thyroid function and and people are over  

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stress and under slept and all these things that  that adding this stress of cold exposure could be   more harmful than beneficial i mean this is how  people say that some people uh what's your take   on on this or who else beyond pregnant woman would  you not recommend that they go into this type of   practice or what is your take on all this yeah so  first of all I say we mentioned the pregnant woman   i would also suggest that or advise that people  with heart diseases and high or low unregulated   blood pressure should also not do the cold water  immersion um this is due to the heart erh and the   activation of the sympathetic nervous system and  the activation of the parasympathetic part of the   nervous system as well where the heart rate goes  up and the heart rate wants to go down and that   is a conflict for the heart to the heart which  is no problem if you are uh healthy and there's  

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nothing wrong with your heart then that is uh okay  because it's very short-term and it doesn't create   any harm to you so this is tested but if you have  heart diseases um or unregulated heart uh high   blood pressure or low blood pressure then this  might be not a good thing for you so um I think   there's been a lot of like and and of course  this happens that people talk online and they   create their own narratives and this but I think  there's lacking a lot of research when it goes   specifically to some specific diseases and whether  this is good or bad for you we still need to uh be   humble about that and say "Hey there's there's  that we don't know." But as as well as I'm as a   researcher saying we don't know then I also think  that people online should stop saying they know   because I mean they can guess all they want but  if you just just a general advice from me is that  

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um if you are very stressed let's say you have  a burnout complete burnout I would not recommend   that you start up doing uh cold water immersion  because putting this although it's very small kind   of intense stress on top of whatever stress you  also have might not be good for you so you need to   relax you know to find other ways to just take the  top of the of the burnout and then start doing the   cold water immersions as part of uh maybe um the  journey that you want to go on to regulate your   your stress but stress definitely is not only  chronic stress right it's also good stress but   good stress when you go to the gym you would also  not use that kind of stress on top of a burnout   so in that sense stress is also just stress so if  you have some kind of h stressed um organ in your  

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body this could be many um when I say stressed  organ in your body it could be you just been   diagnosed with some kind of disease you would want  to get that regulated before you start something   very stressful like uh cold water immersion but  as soon as you get things under control then   you're good for it could a a could a person with  type one diabetes or type two diabetes do cold   water emotions definitely they can if they have  themselves regulated on their medication and also   they measure their blood sugar levels on a regular  basis and I would say especially for people   uh having type 1 uh diabetes when you go into the  sauna you have to measure your blood sugar levels   as soon as you get out because that would increase  your blood cir sugar levels when you go into the  

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sauna and you might crash afterwards so have that  pen with you have your um rotoes with you have   some kind of sugar always be prepared when you do  temperature uh um exposure like this cold or hot   you will clear your blood sugar levels you will  clear fat from your bloodstream but especially the   sugar that is important for people with with any  kind of um diabetes so but that only shows what   I have shown in my research which is that you get  a faster glucose clearance from your bloodstream   and this is super good news but you just have to  be mindful if you have some kind of disease but   you asked about diseases but on a reg I would  say in general this is good for people we are   in a obesity pandemic globally so we want to find  new ways to clear that sugar from the bloodstream   and find new ways to activate the white uh  fat cells in our body and we can do that if we  

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uh use temperature um training or therapy as a  way of activating our metabolism yeah I guess   people there are some people just want to find  excuses not to make an effort you know I'm sure   there there are a lot of people that maybe should  be careful with this type of practice i'm sure but   um I'm also know or understand or I've seen enough  humans to understand that human nature works in   certain ways so a lot of people also like are  looking for excuses not to make an effort and   do things but anyways let's just um go on um  tell me about tell me about shivering um I've   heard you talk about this before um and I thought  it was very interesting we're all we always heard   this story that when we go into the cold either  cold plunging or ice bathing or whatever it is   that we should relax and try to breathe into  the cold and try not to shiver but I've heard  

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you say that maybe it's not such a good idea to  forcefully avoid shivering so tell me more about   this what what's the what's the strategy to follow  yeah you you should not avoid uh the shivering   uh when you get out of the water uh but waiting  in the water until you shiver is not a good idea   because when you start to shiver in the water  this depends on how adapted you are uh and the   more adapted you get the less you shiver m so I  have seen people sitting there in the cold water   online and you see these videos and people like  I don't shiver yet so I will just stay in the   cold water until I shiver which is a bad thing  uh don't do that because as you get adapted to   the cold your muscles start to shiver less and  less you build more mitochondria in the cells and   these mitochondria these are the energy fabrics  in your cells that you have in your muscle fibers  

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you have them in your brown fat cells and these  are are there to increase um energy burning but   also increase the heat in your body so increase  the temperature but as you expose yourself to   something that would decrease the temperature in  your body which is the cold water you your body   would try to adapt and the adaptations that is  increasing the amount of mitochondria in the cells   and when you have more mitochondria you don't  shiver as much okay so when you're in the water   you don't sit there and wait until you shiver you  go up after a few minutes but I always say if you   do contrast therapy so when you alternate between  the cold and the heat um that could be a sauna   that then end with the cold dip because then you  force your body to uh reheat naturally and that is   a super good thing yeah and I don't think many  people know this but when you end on the cold   your activation of your whole metabolism starts  to like go up and you can get dressed and you  

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can just go home and just keep moving uh because  that will also help your body to get back to that   basic temperature which the body wants to but it  takes energy and that is what you have to think   about is a workout for your body where you're not  really doing anything but you're just getting the   extra money out of your cold exposure and you  can stop that by going into the sauna you can   do that but I would just suggest that you don't  let your body reheat naturally because that is so   good exercise for your body yeah I did want to ask  you about that about the sober principle uh maybe   you can tell me more it has a name even it has  a name um but before that um and I didn't invent   it i just want to say that I did I invented the  concept but I didn't name it so yeah somebody did   somebody did this sober principle yeah professor  Andrew Hooperman we we want to say that thank you   andrew was he the one that actually that gave you  that name yeah he he coined the name yeah he asked  

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me about these question these practices and then  I told him why people should end on the cold and   he said that that's that's something he had heard  about or read about in the literature so he coined   it the sober principle so he coined it i didn't  know yeah yeah yeah oh you thought I did that no   no no no i just thought somebody else did neither  you nor him yeah yeah um tell me more about saunas   and tell me about the Finnish sona cohort it's so  interesting yeah I think so too yeah that's Yeah   people need to know amazing right people need to  know about this um yeah please go ahead so uh the   Finnish sona cohorts started uh yeah that's like  25 years ago and some researchers uh asked people   in Finland where they do a lot of sauners um they  do almost everybody is doing sauna there and it's   a part of their culture so they followed 2,500  or 2,300 uh sound bthers for these 20 25 years  

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and made a follow-up each year to measure on all  their health outcomes and when they had done that   for I think it was like 20 years uh in 2015 they  published a paper where they looked at mortality   if people who did sauna each day every every day  or maybe just one two three four times a day or up   to each day so seven times a day a week I mean um  if they had a better health outcome and what they   found was so interesting they saw that if you do  two to three times per week you will have a lower   uh risk of cardiovascular diseases compared to  if you only did one sounder each week and that   doesn't mean that one sounder each week is bad  for you it's just because they measured this up   against a control group who already did s and I  think that is fantastic that they did that they   didn't choose a unhealthy population to measure up  against because of course you have good resource  

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but they actually measured it up against those  who already did once a week and compared that   so two to three times a week had a 40 39%  lower risk of cardiovascular diseases and   um if you did four to seven times sta each week  then you will have an almost 30 an almost 50%   lower risk of dying early compared to those who  only did once a week so it's like the enormous you   could say health benefits that you get from doing  sa uh almost on like a dose response relationship   so the more you can do uh or the often you can  do it so each day maybe then you will have a   cardiovascular workout because that is actually  the the explanation for this right so when you   do sauna you will increase the heart rate you will  sweat and this is the physiological reaction which  

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is increasing your health benefits or lowering  the risk of cardiovascular diseases and there's   actually studies showing that this corresponds  to a zone 2 workout so you can actually do this   workout without moving a muscle just sitting  in the sauna and have that i I don't say that   you should not work out i just say you can add  it on to that and you will have an additional   um lowering component to your risk of uh diseases  but also lowering that mortality is fantastic that   you can do that just by sitting in the heat and  I think people need to know this this is like   um a very long longitudinal study which is it's  cold we don't have that for the cold yet but it   will be very interesting to to have that one  day and we also need some more research which   shows exactly what's going on with the women uh  the the health uh science in women is not as big  

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or as great in this space but there are some some  research out there showing the difference between   men and women when it comes to cold and heat  exposure and there's also some misconceptions   out there you mentioned some of them but but  for women it's just the same do just a couple of   minutes and then you're also good but within your  cycle you could also I'm just answering something   else now but because this study from Finland was  just on men and that is why I want to say that's   actually also the same for women but the women  should just think about it as you can do the same   as men can do it's just that you don't have to  stay in the cold water for example as long uh as   a few minutes or more than a few minutes but it's  the same recommendations that we do for men the   only thing I would say for for women is that when  you are in your cycle um be mindful about when you  

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do the cold exposure and the heat exposure because  you're more sensitive to stress when you have your   period or you're in your new phase so sorry for  just busting that in on top of your of your sona   study i just wanted to get it in there because  so many people ask me this yeah good information   is good information um um so given the health  benefits and um mood boosting effects of cold um   immersion and given the amazing benefits of sauna  do you think there is any study about this uh if   the compounding effects of both practices have  some sort of exponential benefits meaning uh it's   not arithmetically added like the benefits of cold  benefits of sauna put it together is it has has   it some sort of compounding effect by doing them  together I don't know it makes sense the question  

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or if there is any studies that is a really good  question and that is exactly what I researched   in my PhD uh so yeah that that I didn't know  that's a coincidence so I researched in my PhD   um contrast therapy so the alternation between the  cold and the heat and what we see here is when you   push your body right after another so one extreme  temperature to the other extreme temperature you   are also pushing your cardiovascular system which  is a super good workout if you're healthy that is   is completely fine um and of course it takes more  energy and as a PhD in metabolism I always want   to talk about energy i want to talk about if  we could burn some energy and also of course   it's interesting what energy you put in but in  my PhD we really went into burning energy so how   could we lose body from the cold to the heat so  contrasting is within a short time frame a really  

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really a a great workout for your body you need to  adapt so quickly and when your body needs to adapt   from one extreme temperature to the other extreme  temperature that takes energy you need to switch   fast the cells need to be fast at like either  increasing the temperature in the body or actually   get rid of heat in the body so those two extremes  are um energy demanding you can say so that's   where you burn all the energy so what we did in  my study um was that we wanted to look at whether   our winter swimmers who are adapted to winter  swimming for a couple of seasons we compared   those to a control group and what we saw was that  the adapted winter swimmers um they actually had   a better insulin um sensitivity we saw that  they had lower insulin production in the body   uh and compared to the control group and they  also were faster at clearing glucose from the  

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bloodstream uh and that's amazing this is what you  want to see because then you're further away from   getting diabetes and type 2 diabetes is really a  problem these days so you want to do some kind of   um exercise which will help you get further away  from that and as a so these two groups actually   exercised both of them they were young healthy but  what they did not have in common was the uh the   winter swimming and using the sona and they did  this two to three times per week so of course for   people who haven't done this before doing this two  to three times per week might be a be much to push   into your calendar maybe you have family maybe you  have small children i mean start with one times a   week but what we saw was that only 11 minutes in  total of cold water immersion per week divided   on these two to three days and with multiple  dips on these uh these two to three days um  

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corresponding to one to two minutes then you will  have these benefits that I just mentioned for you   um and even more activation of the brown fat what  we also saw that only 57 minutes of sauna per week   was enough also divided on these two to three days  and with multiple saers on these two to three days   then we saw these health benefits so pushing your  body from one extreme temperature to the other is   super good but the next question I often get is  what if you don't have a sauna and a co-plunch   next to each other can we do it on different days  and you can of course you can and you would get   so many health benefits out of that as well and  some similar effects I would imagine but doing   it on the same day definitely pushes your body  even more so that's just logic yeah yeah the   amplitude at which the body needs to adapt from  one extreme to the other adds up um listen I want  

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to be respectful of your time so I'm just going  to throw the very last question related to the   sober principle so we do we don't have to but it's  recommended that we end on cold because of this   um energy effort that the body needs to um make to  bring us back to normal temperature but when we do   saunas and cold plunching we do back and forth  back and forth is there a better way to start is   it better to start with the sauna or is it better  to start with the cold because when I start with   the cold then it takes forever um for me to start  sweating in the sauna right so because the body   temperature goes down so much and there's such  a vaso constriction so is that a good practice   or should I better go straight into the sauna  and then do the cold do you have an intake on   i think it's a good question and and I would say  it would it would be great to have really like a  

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rigid scientific study really I mean pointing  this out but I recommend that you start in the   cold okay that's kind of what I do that's kind  of what I do actually yeah and when you start in   the cold that is where you will activate um also  your um noadrenaline dopamine you'll activate up   oxytocin and oxytocin is really good because  when you sit in the sauna there's probably not   much to do really but when you sit there and you  have this cold chamber afterwards that you sit   there and you're like you feel so safe from uh  from the cold when you sit in so you were safe   by the heat right and you have this increase in  oxytocin in your body that is where you start to   feel gratitude for life you will have change your  chemistry in your brain you have better thoughts   so I always say start in the cold you can sit  longer in dreadful feeling of oh my god I'm  

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already too hot and then you go into the cold  plunge but I mean preferences that is up to   people of course but this is my take on it great  so start with cold end with cold uh thanks a lot   for taking the time where can people know more  about your work or do you have a website are you   on social media where do you think people would  uh get the best out of Susana sober and the best   the best information best information yeah not  the best of me but the the best information so   they can find me on social media uh on  Instagram uh on my name Susanna Soberg   um and they can find me on my website which is  soberinstitute.com i have courses for people who   just want to learn for themselves i also have uh  certifications for people who teach others in this   grace Susanna Sorberg on social media and  all the links to your website thank you very   much for taking the time we had some technical  problems in the middle of it but everything's  

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going to be okay i think so too thank you  Susanna thank you so much for inviting me

Transcript auto-generated by YouTube. Verbatim — duplicates intentionally preserved.

What Happens to Your Brain

The metabolic benefits of cold water are real, but they are invisible. You cannot feel brown fat activating. You cannot sense your cortisol levels shifting across weeks of practice. What you do feel — in the seconds after you step out of cold water — is a fundamental shift in mood. It is swift, involuntary, and complete.

The mechanism is direct. Cold exposure raises dopamine and noradrenaline, two neurotransmitters that govern motivation, focus, and emotional tone. When those levels rise, clarity follows — and whatever you were preoccupied with before you entered the water is suddenly reframed. The problem has not changed; your relationship to it has, because you are now operating with different brain chemistry. That shift is not subtle.

It's impossible to go out in the cold water and have the same state of mind when you go out again.

Søberg calls this the ctrl-delete effect. It is an accurate description. The mental state you carry into cold water is not the one you carry out. The brain chemistry shift is immediate and involuntary — you cannot opt out of it, which is precisely what makes it valuable. It does not require discipline in the water; it requires only that you enter.

The transformation is involuntary in the most useful possible sense. You are not required to think your way into a better mood; the physiology does the work. This is not merely about tolerating discomfort — it is about using cold as a deliberate neurochemical tool, one that resets the baseline of your mental environment with every exposure.

Thirty seconds of cold at the end of a shower activates the sympathetic nervous system's fight-or-flight response. Dopamine and noradrenaline rise, delivering a real return on mood and energy that carries into your work, your relationships, and your capacity for focus throughout the day. The shower cannot replicate the full immersion experience, but it is a legitimate entry point — accessible to almost anyone, requiring no logistics and no special location. The minimum effective dose is lower than most people expect.

Full immersion adds a dimension the shower cannot reach: the parasympathetic diving reflex. When the body submerges in cold water, this ancient neurological response activates alongside the sympathetic stress response — a simultaneous triggering of activation and rest. The result is a state that is alert and grounded at once, the two ordinarily opposing forces brought briefly into equilibrium. A brief cold shower delivers arousal; full immersion delivers something richer.

For those without access to open water or a plunge tub, the cold shower remains a meaningful protocol. The body's response to thirty seconds of cold at the end of a hot shower is not placebo — it is real neurochemistry, real metabolic activation, real mood elevation. The full concept of winter swimming includes dimensions a shower cannot offer. But the shower offers something genuine. Start there if that is where you are.

Duration, Timing, and the Body's Adaptation

One to three minutes is enough. There is no research demonstrating that longer cold water exposure produces greater health benefits — and longer exposure does carry risk. Specifically, it risks the after-drop effect: once you exit the water, cold from the skin continues migrating inward, lowering core temperature further even after you are out. Staying in for ten minutes is not dedication. It is a misunderstanding of how the protocol works.

The timing of your cold exposure shapes everything that follows. Morning is optimal. When you expose yourself to cold in the early hours, the resulting surge in dopamine and noradrenaline delivers a sustained arc of energy, drive, and mental clarity that extends through the full day. You feel the difference in your concentration, in the quality of your focus, and in the presence you bring to the people around you. Morning cold is an investment in the entire day.

Evening cold disrupts sleep. The mechanism is the same one that makes morning cold beneficial: noradrenaline raises arousal and delays the natural drop in core temperature that the body requires to fall asleep. An afternoon plunge can leave you wakeful hours later, just as coffee at five in the evening would. Cold exposure acts on the nervous system with that level of stimulus. Reserve it for the morning; use heat in the evening to accelerate the core temperature drop that initiates and deepens sleep.

Below 15°C, cold water does not feel incrementally colder — it feels categorically different. This is not a trick of perception; it is physiology. Cold receptors activate faster and more intensely at and below this threshold, signaling to the nervous system that something significant is happening. The same four-degree drop from 18°C to 14°C feels far more dramatic than the equivalent drop at warmer temperatures, because the body's sensing system has shifted into a different register.

The body's adaptation to cold is faster than most people expect, and it runs deeper than comfort. As you practice, the sympathetic response becomes more efficient — the initial spike in heart rate resolves faster, the breathing steadies sooner, and calm follows more readily. Anxiety at the water's edge diminishes, not because the cold changes, but because familiarity quiets the alarm. Physical and mental adaptation move together; they are not separate processes.

What is striking about this adaptation is its persistence. Research shows the body retains cold memory for a full year, even after an extended break from the practice. If you pause for months — through pregnancy, illness, or a long winter — you do not return to zero. You come back to a body that remembers the pattern, and the recalibration is faster than the first time. The resilience you build through deliberate cold exposure is not erased by absence; it waits.

The adaptation is incredible fast, and the body remembers this a whole year later — there's actually research showing this.

This persistence shapes how you approach the practice across seasons. Those who begin in late summer, when water temperatures are manageable, find that gradual progression through autumn builds both the physical tolerance and the mental familiarity that winter demands. The body is not surprised by January when it has been learning since September. Seasonal immersion is the most natural form of progressive adaptation available.

Who Should Pause, and Why Ending Cold Matters

Cold water immersion is appropriate for most people in reasonable health. For some, a deliberate pause is the right first step. Pregnancy calls for abstention — the effects of thermal extremes on a developing fetus are not fully understood, and that uncertainty alone makes caution the correct protocol. Unregulated heart disease and unmanaged high or low blood pressure are also contraindications, as the cardiovascular demand of cold immersion places real load on a heart already under stress.

Active burnout belongs on the same list. Cold exposure is a stressor, however brief and beneficial under ordinary circumstances. Adding any stressor to a system already at capacity is counterproductive. The protocol is not wrong; the timing is. Recover first, allow the nervous system to stabilize, and then introduce cold water as a deliberate tool for resilience rather than another demand on a depleted body.

Diabetes requires monitoring rather than avoidance. Cold exposure — like heat — accelerates glucose clearance from the bloodstream, which is a meaningful benefit in a world grappling with metabolic dysfunction. For someone managing blood sugar actively, that acceleration requires awareness: measure before and after, carry what you need, stay prepared. The benefit is real. The engagement it demands is equally real.

After exiting cold water, shivering is not a problem to manage. It is the body's solution to a problem it is already solving. When you shiver, muscles contract rapidly to generate heat, burning fuel in the process — this is active metabolic reheating, and it is valuable. Suppressing the shiver immediately, by returning to a sauna or a hot shower, cuts that metabolic work short. Allow the body to do what it was designed to do.

This is the foundation of the Søberg principle. When practicing contrast therapy — alternating between cold and heat — end on cold, not sauna. Finishing in cold forces the body to do its own reheating, extending the metabolic output of the session beyond the water. You get dressed, move gently, and your metabolism continues working — burning fuel, restoring temperature, rebuilding equilibrium. The reheating window from ending cold is finite and worth protecting.

The Finnish sauna cohort provides the long view on what thermal practice can mean across a lifetime. Researchers followed more than two thousand regular sauna bathers for two decades, tracking health outcomes year after year. Those who used the sauna four to seven times per week demonstrated nearly 50% lower risk of early cardiovascular death compared to those who bathed once per week. The mechanism mirrors zone 2 exercise — raised heart rate, increased circulation, and cardiovascular conditioning achieved through temperature rather than movement. The dose-response relationship is direct: the more frequently you practice, the greater the benefit.

Together, cold and heat are not competing practices. They are complementary protocols, each with a distinct role in the rhythm of recovery and adaptation. Use cold in the morning to prime clarity, drive, and metabolic activation. Use heat in the evening to deepen rest and cardiovascular conditioning. The body responds to sequence as much as it responds to stimulus.