Welcome to Brainstuff, a production of iHeartRadio. Hey Brainstuff. Lauren Vogelbaum. Here picture a brisk morning at the sandy shore of San Francisco Bay. Tony Gilbert is not a former Olympian swimmer. He's not part of a super athlete team, though he knows swimmers like that, and he's not wearing a wetsuit. In his usual swim trunk, swim cap, earplugs and goggles, Gilbert wades into the forty six degree fahrenheit water that's seven degrees celsius, and swims out into the murky Bay.
Gilbert is a hobby cold water swimmer. He's been doing it for over a decade. He returns to shore some forty minutes later, exhilarated for the article. This episode is based on haws toff Work spoke with Gilbert back in twenty twenty two. He said, it's really cold, but we wouldn't do it if it wasn't fun. It's invigorating. Really. The first few minutes are still the worst. Then you get going, the endorphins kick in and you love it. Gilbert is one of the members of the South End
Rowing Club, founded in eighteen seventy three. Who regularly take dips in the frigid bay for fun. Gilbert's swims usually range from twenty to forty minutes, but he's gone as long as ninety minutes. The curious onlookers might wonder how he doesn't experience hypothermia or why he actually enjoys swimming
in such cold waters. It turns out that the human body has evolved some pretty helpful tools to acclimate two different kinds of cold stress when necessary, depending on the frequency, duration, and severity of the cold experienced. Basically, when we need to move around and be comfortable in non life threatening chili conditions, our bodies can habituate to the cold. When the cold gets a little more serious, we can go
through more intense adaptations. To talk about all this, first, let's go over how your body tries to protect you when you experience cold. Okay, human beings are warm blooded mammals, which means that we thermoregulate to keep a stable internal body temperature, usually a little warmer than our environment at which our organs and systems function well. For most humans, that internal or core body temperature is right around ninety seven to ninety nine degrees fahrenheit, which is thirty six
point one to thirty seven point two celsius. We are able to stay right at that temperature because well, a we've invented things like clothes, but b our digestive system and cells break down the food we eat and metabolize the glucose in it into a compound that our cells can use for energy called adenisine triphosphate or ATP, and
heat is a byproduct. When you get too cold, like your body temperature drops below ninety five degrees fahrenheit or thirty five celsius, your organs can't function and begin to shut down, which is bad. This is the aforementioned hypothermia, and it can kill you. So when your body detects a drop in temperature, it has a few defensive measures it'll take to keep your core warm. You might start shivering. This is an involuntary type of muscle contractions that start
in the torso and move to the limbs. What's happening here is your body is attempting to create more internal heat. Your muscles produce some heat whenever they contract through a complicated biomechanical process that I don't understand very well. But this is why moving around can help you warm up. But more importantly for shivering, those repeated and rapid contractions use up ATP real fast, prompting your cells to metabolize
more glucose into ATP plus heat. Of course, your skin is one of the first line systems that your body has to sense the cold, and it has a couple of tricks to pull too. It might go over in goosebumps, which is another type of involuntary muscle contraction, but instead of big muscles giving you big shivers, these are tiny muscles contracting in your skin to generate a bit of heat and raise up your hair follicles, thus trapping a bit of air near the skin and thus holding on
to a little bit of body heat. This might have a negligible effect in humans and work out better for our furrier cousins. But your skin can also perform another involuntary function called cutaneous vasoconstriction. That means vascular constriction in your skin. That is, your blood vessels contract, letting less
blood flow through them at your skin level. You shed heat through your skin, and especially via blood flowing close to skin level, so cutaneous vaso constriction keeps that blood and thus that heat closer into your core to keep your inner organs warm. This is why your extremities your hands and feet get cold the fastest in chili conditions. Your body is trying to keep its heat towards your core.
In these our modern times, we tend to moderate the amount of cold that we're exposed to by bundling up and spending more time in heated indoor areas. But even when we only dip into cold temperatures briefly, even with a minimum of skin exposed, our bodies can habituate to it. We experience habituation, for example, over the course of several cold mornings during ten minute dashes out for coffee or
to walk the dog. Habituations are like physical memory. Instead of wasting valuable bodily energy sending up red flags to your central nervous system. Every time your body is exposed to a cold event, your body remembers it and responds less. Over time, you won't shiver as much, and your skin and extras will stay warmer for longer because your body
won't immediately draw blood inward to protect those vital organs. Basically, your body realizes that the cold isn't going to seriously damage you and that's also not going away, so it adjusts to let you function better in the midst of it. And it's a lot easier to function when you're not shivering and your fingers aren't numb. This is how cold water swimmers can tolerate near freezing water. They habituate to it, but a swimmer can't adjust to swimming long lengths and
cold waters on their first trip. Gilbert said, you have to be regular, consistent with cold water swimming to stay acclimated. You have to swim two to three days a week to stay acclimated, and the few times I did have a break or fall off schedule, I would start back at square one. Start with a short ten minute swim one day, and then the next day try fifteen twenty, and then back to thirty or forty five minutes. Even the best, most adjusted swimmers get too cold and have
to stop when their body tells them it's time. Gilbert said, your body keeps warm at the core, so your extremities can get cold, especially your fingers are toes. On longer swims, you'll even see some people get a claw hand or some people get numb in the lips for a few minutes and slur their words when they get out of the water. This, by the way, is part of why cold water swimmers swim with buddies of form clubs and enlist more experienced swimmers to help teach new hobbyists how
to stay safe. If you're interested, definitely look into organizations in your area. Anyway, Over the past couple of decades, researchers have been looking into another way that our bodies protect us from the cold. It turns out that shivering is not the only cold induced way that our bodies have of producing heat to warm us up. Enter brown fat. Now, body fat in general is a good insulator and can help your core stay warm, but there are different kinds
of body fat, white, brown, and beige. A white fat is the kind you probably think of when you think of body fat. It's made up of cells that store lipids to cushion and insulate our innerds and to save potential energy for a rainy day. It's creamy white in color because each cell is basically just an envelope of lipids, with the cells operative equipment the nucleus and mitochondria squished
out to the sides. Brown and beige fat are so named because they contain a lot more rusty colored, iron rich mitochondria at giving the cells a brown or beige color. When you regularly experience cold, your body starts to activate brown and beige fat cells to basically burn their lipid stores in order to produce heat. For the article, this episode is based on how stuff Works. Spoke with Te Chung Lin, a PhD and Associate professor of biomedical research
at the Masonic Medical Research Institute. He said brown fat serves as a fireplace in our body to keep us warm. Individuals regularly exposed to cold, such as winter swimmers, have higher heat generation efficiency than normal healthy individuals. Some scientists argue that brown fat evolved early on in mammals and helped give us a leg up from other species. Human babies are born with a lot of brown fat to
protect them from cold at birth. Adults tend to retain a little brown fat stored mostly between our shoulder blades. Beige fat cells, meanwhile, seem to arise within populations of white fat cells due to things like cold stress, and then go about burning off their stored energy to help keep the body warm. Researchers are still looking into how brown and beige fat work and how they might be connected to health factors like blood press usure and blood
sugar regulation. There's a hope that if we could figure out how to boost the action of these fats, it might help keep people healthier. So maybe those coldwater swimmers are onto something. Gilbert said, coldwater swimming feels like you're taking a bite out of life. There's nothing else like it. Today's episode is based on the article can our Bodies Learn to withstand frigid Temperatures? On how stuff works dot com,
written by Alison Troutner. Brain Stuff is production of iHeartRadio in partnership with how Stuffworks dot Com, and it is produced by Tyler Klin. Four more podcasts from my heart Radio visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.