In the second episode of the Disney+ docuseries Limitless, Chris Hemsworth dives into near-freezing arctic waters in what he said was one of the toughest challenges of his career.
In the series, which explores science-backed ways to live longer, 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 temperatures in a quest for better health. “Iceman” Wim Hof uses ice baths (along with breathing and meditation techniques) to reduce anxiety and stress. It’s reported that actor Zac Efron, former Twitter CEO Jack Dorsey, and singer Harry Styles have all publicly flexed about submerging themselves in ice-cold water in the name of better wellness.
MORE ON COLD PLUNGE
Cold Plunge Benefits
There’s a reason celebrities have embraced cold plunge therapy: the benefits may be far reaching and have some backing from science. Here’s 10 you should take advantage of.
1. 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 promote recovery and enhance sport-specific abilities after exercise (3).
Cold water immersion alone may reduce muscle soreness 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 cold water (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.
Taking a freezing dip 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).
2. Improves mood
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. One study published in 2021 in Lifestyle Medicine found swimming in cold ocean water improved participants’ moods (7).
While researchers are still sussing out exactly how cold water 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.
3. Upgrades sleep
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.
4. Torches calories
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 and cardiovascular disease (10).
The frigid temperature may also improve insulin sensitivity and fat metabolism (9).
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5. Increases testosterone
The jury is still out on whether icing your balls can improve sperm count, but some small studies have found cold exposure boosted sperm quality.
Without many concrete studies on an ice bath’s benefits to increased testosterone, neuroscientist Andrew Huberman has a couple potential reasons.
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.
KNOW YOUR T
6. Boosts immunity
It’s no vitamin C, but cold exposure increased white blood cells and 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 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).
7. Eases pain
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 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).
8. Takes down stress
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 stress levels 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).
9. 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).
10. Better muscle performance
Getting in an ice bath itself tightens or constricts your blood vessels. The real benefit comes post-plunge.
One study found that after you emerge, blood flow increases and brings more oxygen to your muscles (4). More oxygen means your muscles contract and perform better.
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.
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.
The Bottom Line
There’s plenty of anecdotal benefits to a cold plunge, but more convincing scientific research suggests that an ice bath may relieve soreness, improve mood, promote better sleep, burn calories, and may increase T. Ice baths are safe if you stay within the right time frame and temperature