Of all the possible things someone could do for fun, or a challenge, or even for health, plunging into cold water was at the bottom of my list. In fact, it wasn’t even on my list. My aversion to cold water is so extreme that the last time I swam in the Pacific Ocean, I wore a wetsuit — on Maui.
But on a brisk day in early March, I did the unthinkable and immersed myself into a 39-degree plunge pool — twice.
I did it partly for the challenge, and partly for my health; people who practice cold immersion report less joint and muscle pain, faster metabolism, improved focus, and better sleep. But mostly, I wanted to understand why winter swimmers describe themselves afterward as “ecstatic, peaceful, energized, calm, confident, and alive.” How could something so torturous make you feel so good? And how can you feel simultaneously ecstatic and calm?
“Winter swimming creates an endorphin rush,” says Tahoe City resident Nick Mitchell, who’s been swimming regularly for three years. “It gives you a natural high, because you’ve accomplished something quite challenging, and it puts you in a positive mindset the rest of the day.”
Mitchell began swimming in Lake Tahoe in the fall of 2020 at the height of the pandemic. “I thought it would be good for my mind and focus.”
The experience was so positive, he kept it up. Every single day. For a year.
Using the Instagram handle laketahoe365, Mitchell documented his daily swims and began raising money for charity. He swam in every condition — rain, snow, wind, and even after dark.
Is he crazy? Not according to Dr. Susanna Søberg, a metabolic and stress scientist, of the University of Copenhagen.
Søberg has studied winter swimmers extensively and found that taking short dips of one to three minutes in water 59 degrees or colder increases metabolism, thermoregulation, immunity, and insulin sensitivity. It also boosts mood and eases depression.
Despite being a “cold sissy,” Søberg became a winter swimmer herself, and wrote the book Winter Swimming: The Nordic Way Towards a Healthier and Happier Life.
Though jumping into frigid water may sound dumb (remember the Titanic?), you don’t have to stay in long to reap benefits. The goal is not to lower your core body temperature, but rather to subject yourself to a dose of micro-stress. In doing so, you activate metabolic pathways that repair damaged cells and boost longevity in an adaptive process known as hormesis.
Søberg found that significant benefits were achieved when subjects immersed themselves in cold water for a total of 11 minutes per week, divided over multiple days, a protocol now called the Søberg Principle. There is perhaps no other activity that yields so many benefits in so short a time.
That’s not to imply it’s a piece of cake.
The body’s response to cold water is immediate and complex. As soon as you submerge to your shoulders, you experience cold shock. Temperature receptors in your skin alert the hypothalamus that it’s really cold, and your fight-or-flight response (the sympathetic nervous system) kicks in. You’re flooded with three neurotransmitters: noradrenalin, adrenalin, and cortisol. The most dominant of these, noradrenalin, increases 250 to 400 percent, and constricts blood vessels in your extremities to prevent heat loss in your core. Heart rate and blood pressure temporarily rise.
Within seconds, noradrenalin activates brown fat, a healthy, metabolically-active fat that pulls lipids and glucose from your bloodstream and converts them to heat before your muscles have time to shiver. When activated by cold, brown fat keeps your vital organs warm, and you alive.
Most brown fat is located close to the central nervous system, under the collarbone and along the spine. Though we’re all born with brown fat, the organ diminishes with age unless stimulated by cold — something we don’t experience often in our temperature-controlled lives.
As a newbie to cold immersion, I knew that my first dip would only last a few seconds and would be … memorable. Most first-timers gasp and start to hyperventilate, but this was not my experience.
Heeding Mitchell’s advice, I took a few deep breaths, and stepped into the cold pool. “Go calmly and slowly but without hesitation,” he’d told me. Hesitation, I knew, gives your brain time to process how idiotic you’re being. I lowered myself to the shoulders, counted slowly to five, and got out.
Wrapped in a towel and bouncing around, my first thought was, that was easier than a cold shower. To prepare for this plunge, I’d been ending my showers with a 30- to 60-second cold blast in 55-degree water. The plunge pool, at 39 degrees, was somehow easier.
I let myself shiver in the cold air for a few minutes, then, because I was conveniently at Sierra Hot Springs, I eased into the 99-degree warm pool. A little while later, I plunged again, this time for 17 seconds. (Yes, I counted.)
It was exhilarating; but I knew I’d have to dip again — and for longer — for the magic to happen. According to Søberg, if you dip two to four more times, your body will habituate very, very quickly.
Once you can stay in for 40 to 90 seconds (this varies by person and is aided by breathwork), the experience changes in profound ways:
The parasympathetic nervous system, or “diving response,” kicks in. Heart rate and blood pressure decrease and breathing becomes calm. A cascade of feel-good hormones and neurotransmitters flood your brain and body. Dopamine increases 250 percent, fostering feelings of happiness and contentment, as well as addiction, which is why people love winter swimming and keep doing it. A boost in serotonin makes you feel relaxed and mentally balanced.
Endorphins blunt the pain of the cold and leave you feeling motivated and euphoric. Oxytocin, the “love hormone,” fosters bonding and friendship with fellow winter swimmers. These mood-boosting effects last for hours after a swim.
Cold submersion also stimulates the vagus nerve, an important regulator of the immune system and inflammation; this may explain why winter swimmers report fewer sick days and less joint and muscle pain.
“Since I began winter swimming,” Mitchell said, “my old ankle injury hasn’t bothered me.”
The more you’re exposed to cold, the more brown fat you’ll make, and the more efficient it will be. You’ll stay warmer in cold weather. Your metabolism, insulin sensitivity, and blood sugar control will improve. These benefits have shown potential for improving obesity, type 2 diabetes, and cardiovascular disease.
If you can’t bring yourself to cold plunge, other kinds of cold exposure can activate brown fat. One option is ending your shower with a 30-to-90-second cold blast. Just 30 seconds was enough to reduce sick days for study participants. You can also expose some skin to cold air, or even go snow bathing.
Another option is to lower the thermostat at night. Research found that sleeping in a “cool” 66-degree room for a month increased insulin sensitivity, a benefit that vanished when subjects returned to sleeping in a 75-degree room. It’s ok to pile on blankets; you don’t have to sleep chilled to activate brown fat.
While these non-swimming methods can boost metabolism and brown fat, the only way to get that cascade of mood-boosting hormones is to — quite literally — take the plunge and immerse yourself. If there’s no lake nearby, try filling a bathtub, barrel, or kiddie pool with cold water.
And who knows? Like Nick Mitchell, you just might make it a habit. After reaching his 365-day goal, Mitchell continued his streak for a remarkable 562 days. Now, he swims once or twice a week, especially when there’s a beautiful sunset.
“I’m in this incredible place, looking around at the mountains,” Mitchell marveled. “The water turns pink around me, and I feel like I’m actually in the sunset.”
That sounds almost good enough to try …
Ready to PLUNGE?
Tips and safety for beginners
If you have a heart condition, high blood pressure, or
thyroid problems, cold immersion could be dangerous.
Please consult your doctor.
1. Acclimatize before your plunge with cold showers. Start with
5 seconds and work up.
2. Always swim with a buddy.
3. To lessen the cold shock, allow your skin to cool a bit in the air before submerging.
4. Begin by dipping a few seconds and increase by 10 or 20 seconds each time until you can stay in for one to two minutes. You don’t need to submerge much longer than three or four minutes to achieve benefits. Overexposure exhausts the cells and flattens the benefits.
5. Don’t be macho. New swimmers who linger too long can experience a marked decrease in blood flow to the brain, causing lightheadedness and even fainting.
6. There’s no need to dunk or remain in the water till you shiver. It’s fine to wear a hat and gloves, and to drink a warm drink afterward.
7. If you’re lake swimming, it’s helpful to start in late summer and habituate as the water turns colder.
8. Don’t compare yourself to others. Everyone’s cold tolerance is different, depending on body composition, sex, and ethnicity, and the sensitivity of the nervous system.
9. Don’t cold dip for 4 to 6 hours after strength training, as the chill can temporarily blunt the gains. It’s fine to cold dip before any muscle-building activity.