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Research Rundown: Winter Swimming

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Female winter swimmer running into lake with snow on banks

Brooke celebrates her 40th with a winter swim in Priest Lake, Idaho

Practically frozen with anticipation, I slowly walk into the black, icy waters of my local lake in Washington State in the middle of February. As the frigid waters creep up my legs, my thighs, my hips, I feel confident that I can do this. Then like a ton of bricks it hits my low back, sending a surge of electric-like pulses up my spine. I briefly wonder if I should stop here. As I wade deeper, the cold takes hold of my breath and all of my attention is allocated to inhaling, exhaling, inhaling, exhaling trying to mimic a somewhat normal rhythm. This reminds me of the time my spouse took me to a 3 hour-long meditation and advised me to just focus on my breath. Unlike then, now my breath is all I can focus on and gone is every single thought of past or future. Submerged up to my shoulders, I can feel every inch of my skin burn, then ache, and eventually numb. My spouse flashes me that knowing smile. We’re in this together. This is what it feels like to be alive. We gently dip our faces below the glass surface and take off.*

Many of our friends and family think we’re crazy for doing this and crazier for loving it. But there are many wonderful things about winter swimming that inspire people all over the world to endure the discomfort and pain just long enough to reap its many benefits…some of them grounded in science, others founded in passion.

*My spouse would like to contribute his experience in that dipping the face in the water is where, for him, it all falls apart…

The Junior Mermaids of Bellingham brave the chilly waters of the Salish Sea

Physiological Response to Winter Swimming

International Winter Swimming Association classifies cold water competitions into three thermal categories (1):

  1. Cold Water – 41-48 deg F (limiting distance 1000 m)
  2. Freezing Water – 37-41 deg F (limiting distance 450 m)
  3. Ice Water – 28-37 deg F (limiting distance 200 m)

At these temperatures, your body passes through various stages of  immediate (and not so immediate) physiological responses. As you enter the water, you will experience:

We experience cold shock, also known as the gasp reflex, within the first 30 seconds of entering cold water and lasting up to 3 minutes. This reflex initiates in temperatures as high as 77 F and peaks between 50-59 F (2). It is dubbed the gasp reflex by your body’s inability to hold your breath for more than a second, leading to a sudden inhalation (or gasp) and hyperventilation, followed by an increase in heart rate (greater than 20 beats/minutes) and blood pressure.

And as it’s reflexive, you can’t control it. Which is why it is important to enter the water slowly. Should you experience this reflex after diving in, you will inhale and lungful of icy water and potential drown. Noted….moving on.

A seal, a whale, and a human walk into a bar….what do they all have in common? The mammalian dive reflex. Now this reflex is fu**ing cool….even if you’re not a self-proclaimed physiology nerd. Once your brain has registered that your body has just entered cold water via its plethora of neural receptors, it will implement a series of responses aimed towards preserving precious oxygen. Firstly, it will cause the blood vessels in your arms and legs (many of which supply your muscles) to constrict and shunt oxygenated blood away from said muscles towards your vital organs. Secondly, it will slow your heart rate down by up to 25% in order to conserve the oxygenated blood pumping through your system (3). So, at this point, we experience a huge swing in our heart rate going from an elevated heart rate during cold shock, to a slow heart rate during the mammalian dive reflex. Another reason to check with your doctor before pursuing cold water swimming if you have a heart condition.

Now that we’ve started swimming in this biting, yet blissful, body of water, we should be conscious of signs and symptoms of cold incapacitation. This is characterized by decreased coordination, slower stroke rate, and heavy limbs, all making it quite difficult to swim and possibly exit the water should you have to climb out via a steep embankment. Cold incapacitation happens before hypothermia and is theorized to be responsible for more drowning deaths than hypothermia (4). In fact, hypothermia doesn’t set in until at least 30 minutes in most adults (4), potentially well beyond the time you might want to go for a winter swim. Therefor, cold incapacitation is a good indicator to get the hell out of the water. But how do I test my coordination? Well, if you can’t tell your limbs are not coordinated while swimming, below are a few quick tests you can do in the water to assess coordination. Failure to complete any of these tests indicates lack of coordination.

So, you’ve noticed your arms feeling heavy and were unable to accurately touch your nose and partner’s finger during your safety stop coordination test. Time to get out! But, don’t think your body is done responding to what you just put it through….no way. Your body can continue to cool for up to 30 minutes after getting out of the water due to after drop. After drop is thought to occur for two reasons. One, once you exit the water and the blood vessels in your arms and legs begin to dilate, this cold blood from your periphery begins to circulate back towards the core, lowering your core body temperature (5). Another thought is that a temperature gradient created during cold water swimming of a warm core and cold periphery, begins to balance out as warmth travels from your core to your periphery, causing a lowering in your core temperature (5). Either way, you want to maintain core warmth by drinking a hot beverage and putting on warm/dry clothes. You should NOT jump right into a hot tub or hot shower. This only rapidly dilates your periphery causing an even more rapid cooling of your core temperature.

Female swimmer wading into cold waters
Annie slowly regulates her breathing after cold shock.
If you haven’t noticed, safety concerns and recommendations are at the end of each of these paragraphs. So if the sciencey bit bores the hell out of you, do yourself a favor and just read the last couple of sentences of each section.
Dr. Medical Disclaimer

So Why Do It? Health Benefits of Winter Swimming

Reduce Oxidative Stress

If you’re an athlete, you are  knowledgeable or at least minorly concerned with the term “oxidative stress”. Oxidative stress is the imbalance of free radicals and anti-oxidants in our body. Too many free radicals can be bad, causing damage to our cells and contributing to diseases such as diabetes, high blood pressure, Alzheimer’s, and cancer. Antioxidants, on the other hand,  are good in that they help stabilize free radicals, reducing any negative effects on the body. That’s why foods like gogi berries had their moment as being high in antioxidants. 

When we exercise, we place oxidative stress on our bodies. Sounds bad, but actually it’s good because the more we exercise, the more our bodies adapt to and can efficiently deal with that stress. Well, a Polish study found the same to be true for winter swimming (6). 

Researchers analyzed the blood drawn from 15 healthy, male winter swimmers with a mean age of 23 years over the course of a winter swim season (November – March). During this time, these men swam for 2-5 minutes, 2-3 times per week in waters ranging from 32-59 F. What they found was that markers of oxidative stress decreased throughout the winter swim season. Initially, swimming in cold water sent the body into oxidative stress (similar to exercise), but as the season wore on, the cold temperatures no longer triggered the same stress response, meaning a physiological adaptation to their bodies’ ability to manage stress. While this is a small study, conclusions drawn indicate winter swimming as a possible mechanism for body-hardening, or the body’s ability to tolerate various stressors; however, more research is warranted.

BOTTOM LINE: Winter swimming is a possible mechanism for improving our body’s response to oxidative stress, thereby reducing factors contributing to diseases such as diabetes, heart disease, Parkinson’s, and cancer.

Relieve Pain

It is common practice to relieve acute pain and inflammation from a musculoskeletal injury, disease, or intense workout with ice or cold-water submersion. However, the analgesic effect of these modalities is short term, lasting anywhere from 2-24 hours post-submersion (7). While there is abundant research in this area, there is not so much in the arena of long-term cold-water exposure as in the case of cold-water or winter swimming. However, one small study shows some promising applications of winter swimming for pain relief.

This Finnish study (7) compared changes in hormone levels between two groups of 10 healthy females between the ages of 35 and 45. One group participated in winter swimming while the other group participated in whole body cryotherapy (a cold chamber) for 12 weeks. The winter swimming group submerged themselves in a local pond at temperatures between 32-36 F for 20 seconds, 3 days per week. The cold chamber group were exposed 3 times per week to temperatures of 14 F, -76 F, -166 F, respectively, for 2 minutes each exposure.  

While no significant changes were observed in ACTH, beta-endorphin, adrenalin, cortisol, or pro-inflammatory cytokines, there was a 2 to 3-fold increase in the amount of norepinephrine in both groups. Norepinephrine is a hormone responsible for the relief of acute and chronic nerve pain. This study also cited a previous study in which these levels of norepinephrine in winter swimmers didn’t decline until 8 months after submersion, indicating more lasting effects than single bouts of cold-water immersion.

Bottom Line: While winter swimming does not appear to have a significant effect many hormones, it does significantly increase norepinephrine, a hormone responsible for the relief of nerve pain.

Improve Immune Response

When we think of curing common ailments, hot baths and chicken soup usually come to mind. An icy swim isn’t exactly the most intuitive immune-boost, but there’s research to suggest that cold water exposure stimulates immune system adaptations that make us more resistant to illness and inflammatory conditions. (9) The key takeaway to note is that in inexperienced winter swimmers, prolonged cold water immersion was shown to suppress the immune system. In habitual winter swimmers, adaptation to regular cold water exposures stimulated a more robust immune response. So to be clear, we are not recommending an ice swim as first line intervention when you feel a cold coming on or when you are 7 days into a pesky sinus infection. Rather, habitual cold water swimming falls in the category of “an ounce of prevention is worth a pound of cure.”

Exposure to cold water challenges both the neuro-endocrine system (which regulates hormone release and balance) and the immune system (9,10). Habitual exposure to the same stressor stimulates adaptation. This stress-adaptive response results in a longterm immunity-boosting effect as the systems in your body that respond to stress, disease, and infection become more robust and resilient.

Bottom Line: Regular winter swimming can offer a preventative boost to the immune system, but is not an effective strategy to target acute symptoms of infection or disease, nor should it be considered a single-use remedy.

Mental Health Management

Exercise has long been supported by research as a non-pharmaceutical treatment for depression. Even a modest increase in heart rate for as little as ten minutes begins to release endorphins, often called “the happy hormones” that improve mood and mental sharpness post-exercise. Cold water swimming can certainly be considered an aerobic activity option that has the capacity to release endorphins and improve mood. Based on a handful of published case studies, there is evidence that specifically cold water swimming may offer an even greater benefit than standard aerobic activity when it comes to managing major depressive disorders (MDD) without medication (11).

The scientific literature provides a small amount of evidence indicating that a taper from pharmaceutical management paired with the initiation of a progressive cold water swimming program may allow those suffering from MDD to completely transition off medication (11). The non scientific literature corroborates this with an abundance of personal testimonials in books, films, blog posts, and open water swim forums stating that cold water swimming has helped people to overcome mental health challenges such as depression, anxiety, and grief.

Bottom Line: A small number of published case studies indicate that cold water swimming may be a viable option for non-pharmaceutical management of major depressive disorders. A large number of personal testimonials in spaces outside of published research corroborate that cold water swimming can help people manage depression, anxiety, and grief. 

Prevent Dementia

While not a thoroughly investigated area, some interesting findings are coming out of currently ongoing research out of the UK Dementia Research Institute (8). RBM3, also known at the cold shock protein, has been shown in mice model to slow the progression of dementia and even repaired once damaged cells. Until recently, this cold shock protein had not been detected in humans, until researchers analyzed the blood of winter swimmers.

In this study, researchers compared a group of winter swimmers to a control group of people performing Tai Chi in a cold chamber. Both groups reached a hypothermic core temperature of 93 F. However, only the group of swimmers showed elevated levels of cold-shock proteins. The next phases of research are examining whether or not the presence of this protein has the same effect as it does on mice of slowing the progression of dementia. 

BOTTOM LINE: Winter swimmers show elevated levels cold-shock protein (RMB3); however, it has yet to be determined if this protein slows the progression of dementia in humans, as it does in mice. 

Cold Tits Warm Hearts, an open water swim community in Maine

Community

Community is where much of the magic happens around cold water swimming. After a solo swim, one can walk out of the water feeling less pain, improved mood, and a healthy appreciation for reducing oxidative stress and risk for chronic disease processes that impact mind and body. But truth told, swimming in cold water alone is a) not sensible and b) means missing out on one of the most powerful benefits of the experience: sharing it with others.

In 2019 the World Health Organization declared that loneliness is a major health concern worldwide, and this statement was released before we experienced a global pandemic (12). The COVID19 Pandemic has been the best thing for bringing people to open water swimming since… the glacier melted and covered 70% of our planet in water? Yep, I’m going to go ahead and say that. People are flocking in droves to experience the therapeutic benefits of cold water and community.  Cold water swimming hype-pieces in major publication abound. Social isolation and lockdown be damned- pools may be closed but the lakes and oceans are open, and there’s plenty of room to stay socially distanced in nature. Let’s go swimming! Together!

Pods of swimmers around the world show up for the swim but stay for the tea and company. The Wild and Scilly Mermaids (UK). The Dublin Dippers (Ireland). Cold Tits Warm Hearts (ME). Bellingham Mermaid Brigade and Notorious Alki Swimmers (WA). Outdoor Swimming Society (UK). These are just a few of our favorite examples of vibrant cold water swimming communities. An article in Vogue Magazine about cold water swimming states “it’s like all the sex and all the drugs you’ve ever had but all at once.” If you like those kind of things… you know that orgasms and tripping are usually even better when shared.

Both structured and informal social connection positively impact a healthy mind, body, and spirit, and this is well supported by research. Many studies have shown that social isolation is a significant predictor in risk of death (12,13). Now more than ever, safe and healthy opportunities for connection to community are worth their weight in gold. See what I’m saying? Go for the cold… erm… go for the gold!

Bottom Line: Never swim alone- both for safety, and also so you may experience the powerfully supportive community that surrounds cold water swimming. The mental and physical health benefits of community and social connection are well supported by many research studies.

Before You Dive...

  1. If you are at all concerned about your cardiovascular system, have high blood pressure, or history of heart attacks or stroke, consult your doctor before attempting winter swimming.
  2. Choose a familiar swim spot with easy exits along the shore in case you need to get out of the water immediately.
  3. Swim with a buddy. Never cold-water swim alone.
  4. Ease into the water slowly (no jumping!) and splash water on your arms and face.
  5. Wait until the initial cold shock has passed and you can calmly regulate your breathing before swimming. This generally takes 2-3 minutes.
  6. While in the water, keep swimming to generate heat. No 15 minutes bobbing chatty times in the middle of the swim!
  7. Keep water exposure short and slowly build each week (20-30 seconds at a time). See the recommended time table below. EXIT THE WATER IMMEDIATELY IF:
    • You start to shiver
    • You notice “swim failure” or cold incapacitation – swimming more slowly, or difficulty coordinating your arms and legs
  8. Pay attention to the after drop and be sure to keep warming your body with dry, warm clothing and a hot beverage hours after your swim. See recommended winter swim kit below.
  9. For acclimatization, follow a regular schedule. The folks at Outdoor Swimmer recommend once per week for building cold water tolerance and even provide some temperature recommendations. While these are good guidelines, we’re all unique and should listen to our bodies first and foremost.

Disclaimer: The material presented on the Swimrun Labs website is for educational and informational purposes only, and should not be used to replace the diagnosis or treatment provided by a healthcare professional. 

Winter Swimmers' Fav Kit Items

Other Essentials (not pictured):
  1. Thermos for a hot bevy.
  2. Your favorite cake or sugary treat.
  3. Your favorite swim partner (never winter swim alone!)

References

  1. Manolis AS, Manolis SA, Manolis AA, et al. Winter swimming: Body hardening and cardiorespiratory protection via sustainable acclimation. Curr Sports Med Rep. 2019;18(11):401-415. doi:10.1249/JSR.0000000000000653
  2. Bierens JJLM, Lunetta P, Tipton M, Warner DS. Physiology Of Drowning: A Review. Physiology. 2016;31(2):147-166. doi:10.1152/physiol.00002.2015
  3. Godek D, Freeman AM. Physiology, Diving Reflex. In StatPearls. StatPearls Publishing; 2020. Accessed December 26, 2020. http://www.ncbi.nlm.nih.gov/books/NBK538245/
  4. Tipton MJ, Collier N, Massey H, et al. Cold water immersion: Kill or cure? Experimental Physiology. 2017;102(11):1335-1355.
  5. Nuckton TJ, Claman DM, Goldreich D, et al. Hypothermia and afterdrop following open water swimming: The Alcatraz/San Francisco swim study. Am J Emerg Med. 2000;18(6):703-707. doi:10.1053/ajem.2000.16313
  6. Lubkowska A, Dołęgowska B, Szyguła Z, et al. Winter-swimming as a building-up body resistance factor inducing adaptive changes in the oxidant/antioxidant status. Scand J Clin Lab Invest. 2013;73(4):315-325. doi:10.3109/00365513.2013.773594
  7. Leppäluoto J, Westerlund T, Huttunen P, et al. Effects of long‐term whole‐body cold exposures on plasma concentrations of ACTH, beta‐endorphin, cortisol, catecholamines and cytokines in healthy females. Scand J Clin Lab Invest. 2008;68(2):145-153. doi:10.1080/00365510701516350
  8. Peretti D, Bastide A, Radford H, et al. RBM3 mediates structural plasticity and protective effects of cooling in neurodegeneration. Nature. 2015;518(7538):236-239.
  9.   Shu J, Stevenson JR, Zhou X. Modulation of cellular immune responses by cold water swim stress in the rat. Dev Comp Immunol. 1993 Jul-Aug;17(4):357-71. doi: 10.1016/0145-305x(93)90007-d. PMID: 8375569.
  10. Dugué B, Leppänen E. Adaptation related to cytokines in man: effects of regular swimming in ice-cold water. Clin Physiol. 2000;20(2):114-121. doi:10.1046/j.1365-2281.2000.00235.x
  11. van Tulleken C, Tipton M, Massey H, Harper CM. Open water swimming as a treatment for major depressive disorder. BMJ Case Rep. 2018;2018:bcr2018225007. Published 2018 Aug 21. doi:10.1136/bcr-2018-225007
  12. Bzdok D, Dunbar RIM. The Neurobiology of Social Distance. Trends Cogn Sci. 2020 Sep;24(9):717-733. doi: 10.1016/j.tics.2020.05.016. Epub 2020 Jun 3. PMID: 32561254; PMCID: PMC7266757.
  13. Douglas H, Georgiou A, Westbrook J. Social participation as an indicator of successful aging: an overview of concepts and their associations with health. Aust Health Rev. 2017 Aug;41(4):455-462. doi: 10.1071/AH16038. PMID: 27712611.