Every New Year’s Day in Chicago, several different groups of arguably insane swimmers plunge into the icy depths of Lake Michigan – if it isn’t frozen over, in which case they lie on the ice and make snow angels in their bathing suits. And it’s not just Chicago: Polar Bear clubs seem to pop up wherever there’s a body of water cold enough to make jumping into it an event, mostly as an eye-catching way of raising money for charity.
The Polar Bears might not know it, but their freezing fundraiser may actually be benefiting their health, as well as their chosen cause. Hydrotherapy, or improving health by applying water of different temperatures, has a long history, from the temperature-controlled baths of ancient Rome to the healing spas of Switzerland. It fell out of favor in the United States in the 1900s, as pharmaceuticals started to become more effective, but almost a century later it might be making a comeback.
There are really two groups of advocates for cold water therapy, each claiming a slightly different set of benefits. Some people point to to an intriguing metabolic advantage thanks to the cold-induced production of a special kind of body fat, while others tout the hormetic benefits of cold stress for the immune system, exercise recovery, and overall health and resilience. Here’s a look at both sets of claims.
Cold Therapy for Weight Loss: Brown Fat
The most publicized benefit of cold-water exposure is the metabolic advantage of activating a unique kind of fat tissue known as brown fat. Unlike the more familiar white fat that collects around our hips and stomachs, brown fat burns through calories at quite a high rate, because it has a very important job: raising body temperature.
This has been studied for a long time in human babies. Since they can’t shiver nearly as much as adults, babies need a different way to raise their body temperature, and brown fat fits the bill. By burning through stored energy, brown fat provides thermogenesis (creating heat) without shivering.
Energy doesn’t come from nowhere. Since brown fat is generating heat energy in a cold environment, it has to be getting some other kind of energy from somewhere else, and in a human body, there’s a ready-made source of energy just waiting to be used: white fat. In other words, brown fat is a fat-burning fat, a calorie-hungry internal space heater. One study found that a 3-hour period of cold exposure burned 250 extra calories through brown fat, and those calories came almost entirely from fat.
Until recently, brown fat was thought to almost completely disappear in adults. But recent studies have shown that it’s only absent in some adults: the obese ones. In fact, brown fat is strongly associated with leanness at every stage in life, to the point where children with more brown fat grow up to be leaner adults. Normal-weight adults retain deposits of brown fat around their shoulders and spinal cord, with women keeping more than men, and a wide variety among individuals.
Further research has convincingly demonstrated that cold exposure, especially applied to the areas where brown fat is active, stimulates the growth of brown fat deposits. This is logical enough, since the cold temperature lets your body know that this calorically demanding fat is worth the effort of maintaining it.
So could brown fat be the missing link in the quest for an answer to obesity? And could cold exposure be the key to getting more of it? Not so fast, unfortunately. It’s true that icy temperatures push brown fat deposits into a frenzy of calorie-burning heat generation (increasing the metabolic rate by approximately 25-40%), but there’s a catch: this only works as long as the cold exposure lasts.
Take the example above, where subjects burned 250 calories in 3 hours. In a 24-hour day, this would amount to an additional 2,000 calories burned – but only if you stay in the cold for all 24 hours. This makes perfect sense if you think about it: brown fat burns calories when it has to warm you up, so why would it burn any when you don’t need warming? Like most other claims about “boosting your metabolism,” the idea that just having more brown fat will burn through thousands of extra calories every day is vastly overrated.
Cold Therapy for Weight Loss: Leptin
The calorie-burning powers of brown fat might be overrated, but proponents of the cold water theory also claim a different kind of benefit for weight loss. Brown fat and cold exposure might actually play a more important role in healing the hormonal dysfunctions that accompany obesity.
Specifically, this argument revolves around a hormone called leptin, one of the most important regulators of body mass. Basically, leptin acts as a kind of thermostat that tries very hard to keep your body mass constant by increasing your appetite when your fat stores are low, and decreasing your appetite when your fat stores are high. This is great for lean people, because it gives them a built-in guide to how much they should eat. But it’s also why it’s so gruelingly difficult for the obese to lose weight for good: they’re fighting their own body the whole way. This is called the adipostat hypothesis:
According to this model, obese people get stuck in an inescapable feedback loop where any attempt to cut calories or burn more calories through exercise simply causes their body to respond with an all-out defense of the fat tissue they already have. It’s like opening the window in the summer with the A/C on: your A/C unit will just work harder to compensate and the house will stay cold.
Just like with air conditioning, it’s theoretically possible in this model to lose weight, if you cut calories beyond the body’s ability to respond with metabolic shutdown. In the same way, if you leave all the windows open on a very hot summer day, your house will get warmer regardless of how hard the A/C works. But close the windows – go back to normal eating – and the temperature drops right back down again, or maybe even colder, since it’s still trying to compensate from all the open windows.
The question for weight loss then becomes: what could cause the body to defend such an unhealthily high weight? Why do some people’s bodies “want” to be at 300 pounds and other people’s bodies “want” to be at 150? And what can you do to get your body to “want” a healthy weight?
Obese people, as it turns out, are defending such a high weight because they’re leptin resistant. Their fat mass is producing plenty of leptin (more than enough, in fact) but their body isn’t listening to the leptin signaling. The problem isn’t really the leptin at all; it’s the sensitivity of the leptin receptors.
Here’s where the cold comes in. According to the advocates of cold water therapy, cold exposure improves leptin sensitivity, allowing the body to hear that signal again, and start to defend a lower “set point.” So cold thermogenesis promises to override the adipostat hypothesis, and encourage your body to stop freaking out when you lose fat.
It does seem that brown fat might have some sort of benefit related to this. In obese rats with low levels of brown fat, restoring normal levels of brown fat prevents the metabolic slowdown of weight loss, so rodent studies seem to indicate that there’s some kind of metabolic benefit going on. The actual studies are limited, though, and most of them are in rats (and so they don’t necessarily apply directly to humans). So the leptin-sensitizing effects of cold therapy are interesting, and definitely deserve some further study, but they’re far from proven.
Cold Water Therapy for Weight Loss: Does it Work?
That was a fairly in-depth look at the biology of brown fat and leptin resistance, but hopefully the idea that sitting in ice water could help you lose weight now makes a little more sense. Cold water isn’t a miracle cure that can make up for an overall lousy diet (nothing is that miracle cure), and it doesn’t magically rev up your brown fat to burn thousands of extra calories throughout the day. That doesn’t even make sense: brown fat burns calories by warming you up, so why would it continue to use up your energy reserves when your body temperature doesn’t need to be raised?
It does seem to have interesting potential hormonal and metabolic benefits aside from that, though, most notably regarding leptin. And the evidence from rodent studies suggests that it may be anti-obesogenic even though we don’t know precisely why (remember, we’ve only been studying it for a few years; there’s a lot we don’t know yet).
For further reading, the best-known advocate of cold thermogenesis for weight loss (and everything else) is Jack Kruse. His theory of evolutionary health elevates cold exposure to nearly religious significance, and combines cold adaptation, circadian rhythms, leptin, and seasonal ketosis into one enormous diet and lifestyle protocol that has sparked endless controversy in the Paleo community. It’s certainly interesting, but nowhere near proven.
For a slightly less intense view on the benefits of cold, Ray Cronise discusses it in his TEDMED talk on NASA astronauts and what they learned about cold adaptation (although be warned: you’ll have to sit through some vegetarian nutrition as well). Cronise advocates a much less extreme form of cold exposure (think more swimming in slightly chilly water, less ice baths and numbness), one that’s much more achievable for the average person, and certainly more pleasant.
Cold Water Therapy and Immunity
Moving on from the brown fat/leptin sensitivity issue and the question of weight loss, cold exposure also has a completely different set of benefits stemming from the hormetic stress of the experience itself. Hormetic stress is stress that makes you stronger, by forcing your body to overcompensate for a minor injury. A heavy set of deadlifts injures your hamstrings when you’re doing them, but in response, your body’s repair mechanisms kick into overdrive and build the hamstrings back stronger than they were before.
The same process applies to cold exposure. Specifically, it’s helpful for immunity. The typical narrative about colds goes something like this: if you go out in the cold, you’ll get a cold, so make sure to bundle up and don’t forget your hat! This is true if you overdo it to the point of hypothermia, but exposure just up to the point of adaptation and recovery actually bumps up your immune response: one study found that men who sat for 2 hours at 41 degrees Fahrenheit had higher levels of immune cells after the treatment.
By the same mechanism, swimming in cold water improves antioxidant status – of endogenous antioxidants, so the ones that are really effective. So it seems like as long as you don’t overdo the cold, the slight challenge to your body’s homeostasis just helps keep all your body’s defenses primed and ready to take on an actual threat.
Cold Water Therapy and Exercise
The best-documented effect of cold soaks is for athletes who need to recover from a hard workout. Slapping an ice pack on a sore muscle is the first solution everyone suggests, mostly because it’s cheap, easy, and effective. Cold water immersion gives you the same benefit, but distributed over the entire body rather than confined to one painful area. Two different reviews of the literature (one and two) concluded that while the benefits aren’t phenomenal, cold water immersion does seem to reduce soreness and provide minor performance advantages overall.
There’s also a small but interesting body of research on the effects of cold-adapted training – do athletes perform better when they train in the cold? This article describes how elite athletes have been using core cooling (lowering internal body temperature) to reduce exhaustion in the middle of a workout, making the last few sets feel just like the first few.
Exercising in the cold (like a winter jog, or a swim in a frigid pool) also burns more calories, of course, because your body has to work to keep your temperature up as well as to move itself around. On the other hand, if “exercise” means “running in three inches of slush,” it’s very tempting to just skip it altogether: it’s better to build long-term exercise habits than to torture yourself in the attempt to eke out every last calorie, and then hate it so much that you quit.
Cold Water Therapy: Other Benefits
A few other fringe benefits are worth mentioning. Cold immersion increases testosterone and sperm counts in men, so if a romantic dip in the ocean at sunset in October is your idea of a perfect date night, science can provide you with a handy justification.
Alternating hot and cold water in the shower can also help improve circulation, although don’t get caught up in exaggerated reports that it somehow “removes toxins” from the body.
There’s also been some interesting research lately into cold water therapy as a treatment for depression. One study found a significant benefit, but their tests did not include enough people to be significant, and the authors concluded that their research was preliminary and incomplete. Anyone who’s ever woken up to a freezing shower can attest that it’s energizing once you get out; whether this actually translates into a benefit for people with a psychiatric illness remains to be seen.
Dangers of Cold Water Therapy
Proponents of cold water soaks like to play up the amazing achievements of cold-adapted swimmers, hikers, and adventurers, like Wim Hof, the Dutch “iceman” famous for his use of meditation techniques to endure extreme cold for long periods of time without apparent physical damage. But it’s also important to look at the risks for the rest of us.
The most obvious danger of cold exposure is hypothermia, which is mostly dangerous because it’s so sneaky. As well as your physical temperature, it also affects your mental ability: people drowning in cold water often resist help because they don’t understand that they’re in danger. They might not even feel cold. Water colder than 60 F (around 16 C) and air colder than 32 F (0 C) can be deadly and by the time it’s happening to you, you won’t be in a position to realize what’s going on.
This is most obviously a danger for people who take “cold thermogenesis” to mean “jump in the lake in February,” but there’s nothing to prevent it if you stay too long in an ice bath before you’re ready for it, or because you’re trying to prove how tough you are.
Frostbite is another risk. Dave Asprey details here how he tried to follow a cold thermogenesis protocol and ended up with severe frostbite over his chest and arms – so start slowly, and don’t go packing on the ice until you’re used to it.
The initial plunge in can also be a shock. Called the “immersion reflex,” this is the sharp breath in, the faster breathing, and the rapid heartbeat that you feel when you first plunge into a cold shower or pool. For someone with any kind of pre-existing heart problem, it has the potential to turn out very badly. This response drastically decreases if you ease into the water slowly, or after a few sessions of plunging into cold water.
Another risk is a medical condition not often seen in the days of winters spent indoors: chilblains. These painful sores, usually seen on the hands and feet, are simply a response to cold and wet conditions; some people get them, while other people don’t. If you happen to be among the unfortunates, cold water immersion therapy is probably not for you.
Cold Water Therapy: Conclusions
Cold water therapy really falls into the category of “interesting, but not magical.” From a metabolic perspective, brown fat is not a magic bullet, although it may have some interesting effects on leptin and appetite. Just because brown fat is correlated with leanness doesn’t mean it necessarily prevents obesity, or that stimulating brown fat deposits is a magic cure for the overweight. On the other hand, the research in human adults is so new that it’s hard to say anything definitively, and it’s certainly possible that it does have important benefits that we don’t know about.
On a hormetic level, the benefits of cold water are more modest, but slightly better-documented. There’s certainly not much to be said against cold showers, and aside from everything else, they’re a great way to wake yourself up in the morning, or clear your head without resorting to stimulants like caffeine. And on the positive side, cold water therapy is free, easy, and available everywhere
Overall, while it’s not proven as a cure-all therapy for anything, the research that we have and plenty of anecdotal evidence suggests that there are benefits from cold water exposure, as long as it’s kept to a reasonable level. If it works for you, go for it; if you’re curious, there’s no harm in trying it, but think of it as an adjunct to an overall healthy diet and lifestyle, not a replacement for a solid foundation.