Here is a repost of my entry over at the
, a site run and maintained by the UVM Field Naturalist graduate students. If you like this entry, I highly recommend checking out the weekly posts by the rest of my talented colleagues!
One good thing about a mild winter is we avoid that familiar experience of leaving a warm house to enter the arctic interior of a frosty, morning car. Imagine sitting down in that frigid seat: Your shoulders tense and tighten like old taffy, you shiver spontaneously, and the chill leaks into your soul at the space between your pants and socks. Your heart accelerates and your blood pressure spikes. Eventually, either your mental resolve or your car’s heating system recalls you from distress.
Your rational mind knows that things could be a lot worse, so why does our very evolution invoke this intense response anyway? When hit with cold, skin receptors tell the brain to dump a hormone into our system that forces all these unpleasantries. And being cold is so intensely unpleasant because the same chemical, norepinephrine, also floods your body in times of fight-or-flight-style crisis. According to your system, this is an emergency, so your body reacts by pulling out all the stops to maintain core temperature. Veins constrict, shunting your warm blood away from the skin and extremities to prevent heat loss. Your muscles tense to double metabolic heat production, or you shiver to increase it tenfold.
This response is handy for someone freezing to death on a mountainside, but is a supreme overreaction to sitting in a cold car. The reaction is the same because an uncalibrated nervous system doesn’t know the difference between chilly air and certain death, so it plays it safe by overreacting to everything. The body is trying everything it can to maintain homeostasis (that magic core temperature of 98.6 degrees).
Fortunately, like any good piece of hardware, the human body can “winterize.” Regular and sustained exposure to cold trains the body to react more measuredly. After a couple weeks, the brain no longer pays as much attention to unhappy skin receptors. The norepinephrine dose attenuates, and with it the body’s response: Vasoconstriction diminishes, circulation is maintained to the hands and feet for longer, and body temperature can dip before shivering commences. When these responses are really needed (when it gets really cold), they feel less psychologically distracting. This is ultimately why we can wear a t-shirt on the first nice day in April, but need a jacket at the same temperature in September.
Spend enough time in the cold, and the body acclimatizes in extraordinary ways. Instead of vasoconstriction, blood vessels in an Inuit’s hands dilate: His hands receive extra warm blood so he doesn’t lose manual dexterity. Australian aboriginals, who experience near-freezing temperatures every night, can comfortably sleep nude— and actually enter a mild hypothermia to conserve energy— at temperatures that make most people shiver uncontrollably. Some of us even develop special heat-generating fat deposits (called brown fat) around the organs that we recently assumed were only found in human infants and cold-hardy wildlife. Cold temperatures activate brown fat production, and subsequent cold activates its metabolism— the body’s equivalent of stacking firewood to burn for warmth later.
We will never be able to weather the cold like a polar bear, or even like the chickadee chirping delightedly on a bird feeder at -20F. After all, we are a species of naked apes that crawled out of Africa’s tropical rift valley. So how do some of us live perfectly happily in conditions cold enough to freeze snot? Perseverance and willpower, the traits we often find backing most impressive human endeavors, are again the assets that carry us to our biological limits. So while we wait for winter to truly hit, prepare yourself with some light suffering. In a rude example of literally “no pain, no gain,” our affinity for hot cocoa and wood fires during the holidays just prolongs our discomfort once we actually make it outside. A little chill today will winterize your body for the months ahead.
For more on winterizing yourself, check out:
in the American Journal of Human Biology
Wouter D. van Marken Lichtenbelt’s
in the New England Journal of Medicine
in the Journal of Applied Physiology