I live close to a beach in San Francisco with a very cold ocean and walk there most days. I was delighted to find that there is a community of swimmers who brave the cold to swim daily. The water temperature today is 45F (7C). For reference, this is a temperature that one cold water swimming guide puts in the category of “Effing cold”. The guide characterized this temperature as “painfully cold and not recommended for anything other than very short swims (5 to 10 minutes) unless you are very experienced.”
The community of beach swimmers are mostly fit middle aged to older folks, with a giddy and blissed out vibe. There are ladies in their 60s and 70s with four pack abs, something I have never achieved even in my prime playing college tennis. One of them told me that a lot of them are teachers who swim after school lets out. They bring a tent outfitted with a heater as a makeshift sauna. I have a crush on this whole operation and am slowly trying to be brave enough to join their ranks regularly.
I have been swimming since I was a kid on swim teams and in oceans and lakes. This is the coldest and most potentially dangerous swimming venue I have tried out. A big sign saying “swim at your own risk” and “people have drowned” adorns the entrance to the beach. One of the swimmers told me a story of a friend getting stuck in a whirlpool current that they couldn’t swim out of and almost drowning before search and rescue found them. Lessons learned included “wear flippers so you can better swim out of currents” and “don’t wear a silver swim cap because you blend into the ocean and are harder to spot by rescue”. That almost drowning person reported a feeling of euphoric ecstasy as their body temperature dropped into hypothermia. Hey, at least that sounds like an ok way to go.
One reason that I am interested in swimming in the ice cold ocean water is that it is at least rumored that cold water immersion has health benefits. I decided to take a read of the scientific literature to see if there was anything to this or if I was braving the cold for no reason. I started by searching pubmed (my search is linked here if you want to play along at home) for reviews on cold water health benefits. Funnily enough there was a paper written on San Francisco Bay cold water swimmers. The paper concludes that while SF cold water swimmers had lower BMIs than the average person in the US and the average person in SF, they had the same BMI on average as pool swimmers in the US. This suggests that the benefit of cold water swimming (at least on BMI) is due to the swimming part, not the cold water part.
I found another review paper that was a pretty interesting read, “Cold Water Swimming—Benefits and Risks: A Narrative Review”. They did the hard work of reading >1,000 papers on the topic and summarizing their findings. They also give some historical context on cultures that ice water swim. They conclude that “Regular swimming training in cold water seems to have a positive effect on various systems such as the cardiovascular system, endocrine system, immune system and the psyche.” Although, I’m not super convinced because the quality of evidence is pretty low in all the studies- they are mainly case reports and cross sectional studies. The biggest problem with many of these studies is that they don’t tease apart what is a benefit of swimming in general vs. swimming in cold water. The gold standard for evidence would be a randomized control trial comparing people assigned to pool swimming vs. cold water swimming. This, to the best of my searching, has not been done.
They do point out some other risks beyond drowning and hypothermia that I wasn’t aware of, including cardiac arrest risk due to arrhythmias. That is a good reason to go slow and work up to a full swim in case you have an underlying heart condition that you aren’t aware of. I am probably clear of that risk at this point having swum in the cold a few times.
Another paper dunked about thirty people in ice water for 5 minutes and reported elevation in mood afterwards. It’s hard to know though how much of that effect was placebo but it seemed positive in any case. I went on a brief tangent into the literature about cold water immersion for sports recovery and found that surprisingly that has negative effects on athletic recovery. So trainers beware of suggesting athletes work out and then ice bath.
I then decided to turn up the heat and investigate the health benefits (and potential harms) of sauna bathing. You can play along at home with my search here. Sauna bathing has a lot more high quality evidence for health benefits than ice swimming. There are even meta-analyses published and spoiler alert it appears overwhelmingly positive. Mayo clinic reviews the evidence in “Cardiovascular and Other Health Benefits of Sauna Bathing: A Review of the Evidence”. Here is what they have to say
“Beyond pleasure and relaxation, emerging evidence suggests that sauna bathing has several health benefits, which include reduction in the risk of vascular diseases such as high blood pressure, cardiovascular disease (CVD), stroke, and neurocognitive diseases; nonvascular conditions such as pulmonary diseases including common flu; mortality; treatment of specific skin conditions; as well as pain in conditions such as rheumatic diseases and headache.”
I dived into why sauna might be beneficial and found some interesting theories. More evidence is needed, but the thinking is that the salt release from sweating is good for blood pressure and may even counteract the eating of salt preserved fish in sauna bathers in Finland. Sauna also raises heart rate like exercise does- giving your heart a workout without doing the actual exercise. This is especially beneficial in folks who can’t exercise or for whom exercising is difficult. The positive health benefits were dose dependent- meaning going multiple times a week was better for health than 1x/week.
In conclusion, swimming is good for you. Ice swimming might be better than pool swimming although you should weigh the risks of, say, drowning, hypothermia, and heart arrhythmias. If you do decide to take the icy plunge into winter swimming, wear flippers and a brightly colored swim cap, and ease your way into it. Cold water immersion probably is good for mood but isn’t ideal for sports recovery. Sauna is A+ and going more times a week is better than going just once. I think I might have to buy a sauna membership- don’t threaten me with a good time:)