During the second episode of the Disney+ docuseries Limitless, which explores science-backed ways to live longer, Chris Hemsworth dives into near-freezing arctic waters in what he said was one of the toughest challenges of his career.
In the series longevity expert Peter Attia, M.D., explains why Hemsworth was turning himself into a Thor-sicle: exposing your body to extreme cold has healthspan-extending benefits.
Some research suggests that sitting in a tub of ice water may help reduce inflammation, boost blood flow, improve immunity, and manage pain (1). It may also lower cortisol levels (2), your body’s stress-inducing hormone.
Hemsworth isn’t the only big name to embrace freezing water temperatures in a quest for better health. Extreme athlete “Iceman” Wim Hof uses ice baths (along with breathing and meditation techniques) to reduce anxiety and stress. Scores of other actors, professional athletes, and Silicon Valley tech geniuses have also publicly flexed about submerging themselves in ice-cold water for their well-being.
More importantly, longevity experts like Attia have also weighed in on the potential physical and mental health benefits of cold therapy, including its potential to extend your healthspan and lifespan. So whether you own an ice bath or are just dabbling with cold showers, here’s what you’d reap by freezing your ass off.
Benefits of Cold Plunging
There’s a reason athletes and longevity experts alike have embraced cold plunge therapy: the benefits may be far-reaching and have some backing from science. Here are 10 you should take advantage of.
Relieves muscle soreness
Tennis pro Andy Murray needed an “emergency” ice bath after a grueling match at the 2020 U.S. Open. “My body hurts and I need to recover as fast as possible,” he told a reporter after the match.
When done in tandem with a cool-down exercise routine, cold water therapy can boost athletic performance by promoting recovery and enhancing sport-specific abilities after exercise (3).
Cold water immersion alone may reduce muscle soreness post-exercise and increase perceived recovery. In one study, the perception of muscle soreness was significantly lower 24 hours later in the subjects that were immersed in a cold bath (4,5). Ice baths can also lower levels of lactic acid—the fuel for your cells during intense exercise and the source of that burning sensation in your muscles post-workout.
Cold plunging regularly may have even greater recovery perks. One study published in 2020 found cold plunges had long-term recovery benefits on fatigue, soreness, and wellness in highly-trained volleyball players. The subjects had 10-minute sessions once each for 12 days in 50-degree Fahrenheit water (6).
If you’re looking for major gains post-workout, however, you might want to skip jumping in a cold plunge tub or taking an icy cold shower. In a recent episode of his podcast, The Drive, Attia points to research suggesting cold water therapy may reduce hypertrophy—muscle cell growth after resistance training.
“You’ll want to minimize your use of it after resistance training if your objectives are strength and or hypertrophy,” Attia says. “If you’re doing more high-intensity training, especially training that has a focus on eccentricity, like running, and you’re not as concerned with strength and hypertrophy, then the trade-off might be worth it.”
In a post-Limitless Instagram post, Hemsworth said cold plunges boosted his mood. “I think it’s because when you’re in here, you feel like you’re dying,” the actor joked while sitting in an ice bath. “And when you get out, you feel like you’re alive again, which makes you very happy.”
Research backs him up. Swimming in cold ocean water improved participants’ moods once they got over the initial shock of the cold (7).
While researchers are still sussing out exactly how cryotherapy lifts mood, neuroscientist Andrew Huberman has a theory: He suspects that cold exposure releases dopamine—the “feel-good” hormone which boosts mood, energy, and focus as well as endorphins.
Attia suspects other neurotransmitters could also be impacted. In his podcast, he references a small study from 2000 that studied the neurotransmitter response of ten young men who participated in one hour of head-out-of-water cold water immersion at 57 degrees Fahrenheit (17). Researchers then tracked their plasma norepinephrine, a neurotransmitter that controls your body’s fight or flight response, levels. They found that participants’ norepinephrine levels increased more than 500 percent during the cold exposure.
“This neurotransmitter response is one of the reasons we think cold therapy might be a viable tool for depression,” Attia explains. “It’s still not entirely clear what the mechanisms of action are in the brain, but I will say subjectively most people find it very mood stabilizing to have even a fraction of the cold immersion from these studies.”
Some research suggests warm showers can help you fall asleep faster. But cold water may help you sleep better too.
One study published in the journal Frontiers in Sports and Active Living (8) found that subjects who submerged their whole bodies—including their heads—in cold water after high-intensity, intermittent running exercise reduced limb movement and increased slow-wave sleep—thought to be the most restorative stage of sleep, the form of deep sleep where your body recovers.
This stage may also help boost your immune system, and there is some evidence that deep sleep may contribute to memory, creativity, and insightful thinking.
Don’t sell your Peloton just yet. One review of current literature published in 2019 found cold exposure activated brown adipose tissue—brown fat—making it work harder to help your body burn more calories (9).
A more recent meta-analysis of 104 studies found cold water swimming seemed to reduce or transform body fat, which can protect against diseases, including diabetes, cardiovascular disease, and cardiac arrest (10).
The frigid temperature may also improve insulin sensitivity, blood glucose regulation, and fat metabolism (9).
The jury is still out on whether icing your balls can improve sperm count, but some small studies have found cold plunging boosted sperm quality.
Without many concrete studies on an ice bath’s benefits to increased testosterone, neuroscientist Andrew Huberman has a couple of potential theories.
Hormones, including testosterone, travel through the bloodstream. When you cool any part of your body, your blood vessels constrict. When you warm up again, more blood will flow to that area. “So perfusion of that region, and the gonads to be specific, with additional blood, you could imagine in some ways increasing testosterone, that’s reasonably plausible,” Huberman said on his Huberman Lab podcast.
A more likely reason involves dopamine, he says. Cold exposure increases your dopamine release, “and dopamine is known to be in the pathway that can stimulate testosterone,” he said.
“While there isn’t a direct relationship between dopamine stimulating testosterone, there is an interesting pathway whereby dopamine increases can trigger increases in things like luteinizing hormone, which can trigger increases in testosterone,” Huberman said.
It’s no vitamin C, but cold exposure increased white blood cell count and the number of natural killer (NK) cells, which fight infection and protect against disease, in a review of articles published in the North American Journal of Medicine and Science (1).
One study from the Netherlands found people who ended a warm water shower with up to 90 seconds of cold water for 30 days called in sick from work less than people who took showers at their regular temperature (11).
Aside from exercise-induced muscle soreness, there is evidence that an icy plunge may help relieve chronic pain.
One study published in 2022 found people with autoinflammatory arthritis had less joint pain and a better quality of life after immersing themselves in cold water immersion for 20 minutes a day for four weeks (12).
Other research has suggested that whole-body cold therapy or ice swimming may reduce pain perception, possibly because the cold temperatures cause the body to release norepinephrine, a neurotransmitter involved with your fight or flight response (13).
Decreases stress levels
Cold water immersion slows your heart rate and directs blood flow to your brain, which may dethrone stress by stimulating your vagus nerve.
Your vagus nerve runs from your skull, down your neck, through your thorax and into your abdomen, touching almost every organ it passes. Its main job is to regulate internal organ function, including digestion, heart rate, and breathing rate.
The vagus nerve also helps regulate your nervous system, assisting it in switching between your parasympathetic mode—known as the “rest and digest” mode—and your sympathetic mode, or “fight or flight.” When levels of stress rise, your sympathetic mode becomes overactive, and your vagus nerve triggers your parasympathetic mode to calm you down.
One study published in 2018 found that when cold stimulation was applied to participants’ neck area it increased their heart rate variability and lowered heart rate more than in the control group (14)—they can be signs of being less stressed and happier.
Another study found that when combined with sauna, cold water immersion decreased levels of the stress hormone cortisol (2).
Raises insulin sensitivity
Insulin sensitivity describes how responsive your cells are to insulin. If you have low insulin sensitivity, you may have higher blood sugar levels, which puts you at risk for health problems including high blood pressure, heart disease, and obesity.
Studies have found cold exposure increased insulin sensitivity in people with type 2 diabetes (15,16). Why this matters: the more insulin sensitive someone with Type 2 diabetes is, the less medication they’ll need to reach optimal blood sugar levels.
One review published in 2022 found cold exposure to water or air increased adiponectin—a protein produced in your adipose tissue that plays an important role in protecting you against insulin resistance, which can result in elevated blood sugar which can put you at risk for prediabetes and Type 2 diabetes (9).
Cold Plunge Protocols
Cold water immersion
Think: your typical Wim Hof-style ice bath. For this protocol, you’ll submerge your entire body in a tub of cold water (with or without ice). And Attia says you don’t need expensive gear to start this protocol.
“When I started doing it, I would just go out and buy ice at the grocery store and stick it into my bathtub,” Attia says.
Unlike CWI, you’ll need to go to a dedicated cryotherapy facility for this cold exposure protocol.
During this procedure, you’ll “stand in a tube that blasts liquid nitrogen” for around three minutes. Attia says that you can expect temps around -160 to -260 degrees Fahrenheit.
“You might say, ‘How can a person tolerate that?’ You have to remember there’s a totally different conductivity of gas versus liquid,” Attia says. “Because it’s a gas coming at you, it’s not going to be as capable of extracting heat from your body. Anyone that’s done both will tell you that cold water immersion is subjectively colder.”
How Long Should You Stay in a Cold Plunge?
The general consensus for a safe cold plunge is anywhere from four minutes to 20 minutes in water between 50 and 59 degrees Fahrenheit. Start with a few minutes, and build up over a few weeks as you get more acclimated to the temperature.
Attia recommends only spending two to three minutes in cold plunges under 40 degrees Fahrenheit. For 30-minute sessions, keep temps above 50 degrees.
Don’t have a thermometer on hand? Huberman told the Modern Wisdom Podcast that this temperature range feels, “cold enough that you really want to get the hell out but you can stay in safely.”
When you emerge from an ice bath, don’t rush to a steaming hot shower. Immediately take off the wet clothes, put on warm, dry clothes, and drink something warm so that you let your body slowly heat up, Tracy Zaslow, M.D., told Cedars-Sinai. A hot shower too soon after cold temperature exposure will, “cause your blood vessels to relax or dilate, and you could pass out,” she said.
How Much of Your Body Should You Submerge?
Soaking is a tool to help optimize recovery and to help you reap benefits including better sleep, stress relief, and an immune boost. Ideally, you’ll submerge your whole body, says Jaclyn Cunningham, MA, ATC, Assistant Athletic Trainer at Ohio State University.
For beginners, “work your way into it,” Cunningham says. “Start by going in up to your knees, then progress to your hips, to your chest, and finally full submersion.”
More adventurous plungers can dunk their heads—just not for the entire session, she says.
How Often Should I Cold Plunge?
You can take an icy plunge two to five times per week, Cunningham says.
While an ice bath post-workout is encouraged, steer clear of a pre-workout plunge—it delays your body’s reaction time and limits your strength, says Cunningham.
Cold Plunge Risks
An ice bath comes with normal cold exposure risks, including hypothermia, so don’t stay in more than 20 minutes and keep the temperature ideally at no less than 50 degrees, Cunningham says.
If you have a heart condition or take medications like beta blockers that lower blood pressure and heart rate, the sudden temp drop can be a shock to your system. Talk to your doctor before plunging in if you have an existing heart or health problem.
Scientific research suggests that benefits of cold water immersion may include relieving sore muscles, improving mood, promoting better sleep, burning calories, and increasing testosterone. Ice baths are safe if you stay within the right time frame and temperature.