Monday, November 17, 2014

Apple #689: How the Body Adjusts to Cold Weather

The temperatures are starting to drop, some parts of the country have already gotten snow.  But it struck me last week, when temperatures fell from a surprising 70 degrees down to 45, how different 45 degrees feels at the end of fall versus what it feels like at the beginning of spring.

This time of year, when it hits 45, everybody starts pulling out their heavy coats and winter sweaters, putting on gloves and hats, blowing on their hands to keep them warm.  In the spring, that same 45 degrees feels luscious.  Everything's melting, the sun is out, the air feels balmy, everyone's unzipping their coats, going bare-headed and without gloves.  So what's the deal?

Like it or not, cold weather is coming.  Are you ready?
(Photo from Ask Bob Carr)

I've always thought the fact that we react to the same temperature so differently depending on the time of year was all a matter of perspective.  Context.  It's been warm, now it feels colder, and ooh boy, we don't like it.  Or, it's been cold, now it's warming up, and ooh boy, that's nice.

I looked this up (as your fearless Apple Lady is wont to do) and it turns out, it is not just in our heads.  It is in our bodies, too.

  • Scientists estimate that it takes our bodies somewhere between one and two weeks to adjust to a major change in temperature.  This could be cold weather becoming warm, or warm weather becoming cold.
  • But we are better at adjusting warming temperatures rather than warm temperatures becoming cold.  As one anthropologist says, our bodies are better adapted to warm weather and "Our bodies are just not as good at dealing with cold."
  • But our bodies do make some adjustments.
  • First, you get goose bumps.  This doesn't actually do all that much for us anymore now that we humans aren't covered with a coat of fur.  But if we were still furry like our animal relatives are, the constriction of the hair follicles would lift the individual hairs slightly above the skin, trapping warm air beneath the fur and giving us an extra layer of insulation.  As I said, we don't have fur anymore, so even though we still get goosebumps, they don't do us that much good.

See how the goose bumps make the hair stand up?  Now, if this were long and densely packed animal fur instead of sparse and thin body hair, you can imagine the warm air that would be kept all nice and cozy under there.
(Photo from Beliefnet)

    • By the way, the big scientific word for goosebumps is "horripilation." This is because animals' fur stands up not just when they're cold but also when they are threatened and want to scare the heck out of any would-be attackers, a.k.a. they want to make themselves look horrifying. 
  • The next cold weather response is that our muscles shiver.  This is a fast way of producing a lot of heat -- 5x the amount of body heat prior to shivering.  When we shiver, our muscles contract rapidly over and over.  But since shivering expends a lot of energy and it doesn't do much else for us, shivering is typically a short-term solution, one that our bodies abandon if the cold persists for too long.

Yes, this is bad clip art, but it gets the idea of shivering across.  Also, see how he's got his arms crossed in front of his chest?  This is another unconscious response to the cold that we often have.  We are trying to warm up and protect the most important part of our body: the core.  So this guy may look cold, but his body is trying its best to keep him warm in spite of the cold.
(Image from Clipart Panda)

  • The next thing, and the longer-term solution, is our blood vessels constrict.  Your body is trying to manage blood flow, and since blood carries heat with it, it's trying to be judicious about how much heat it's sending where.  It doesn't want to send too much blood/heat to the extremities like fingertips, toes, end of the nose because those parts of the body are not as essential as things like the internal organs and the brain.  
    • I don't know about you, but I have noticed when I'm out walking in the winter for any length of time that I might feel chilly in my hands and face, but I'm snug as a bug in my torso.  This is the blood vessel constriction plan working very well.

Cross-section diagrams of blood vessels. At the left is what the blood vessels normally look like, in the middle is what blood vessel constriction looks like, and finally at the right, what blood vessel dilation looks like.  It's not that the blood vessels themselves get bigger or smaller, but rather that the muscle cells in the blood vessels expand or constrict, allowing more or less space in the vessel for blood to pass through.
(Diagram from Wikipedia)

  • But your body is not so draconian that it believes it can entirely abandon your fingertips, toes, and end of your nose.  Those things are pretty helpful.  So it will periodically stop doing the constriction thing and switch to dilation -- expanding the blood vessels to allow blood flow back to the extremities to keep them nourished and from getting so cold they get frostbite.  
    • When your cheeks turn red from cold and your nose turns pink, that's blood vessel dilation happening.  The pink in your cheeks is the extra blood flow going to your face.

These people's faces have turned pink because their bodies are trying to keep their faces warm, even as it's cold outside.  Blood vessel dilation in the face at work.  (These people are in Iceland, by the way.)
(Photo from TripAdvisor)

  • If you stay out in the cold and your body has to continue to deal with it, your body will switch  again from dilation back to constriction.  Because really, those internal organs are pretty important.  After enough time in the cold, your body will make that brutal decision to sacrifice your fingertips, your toes, or the end of your nose if it has to.  This isn't some namby-pamby parlor game, after all.  This is the preservation of your life we're talking about here.
  • Something else that happens along with blood vessel constriction is an increase in blood pressure.  Less room for the blood to move around in, the higher the pressure on the blood vessels.  This is why, for example, people are more prone to getting heart attacks while shoveling snow.  
  • But what's more likely to happen before you have a heart attack from elevated blood pressure is that your body will try to reduce the pressure by reducing the amount of fluid in your system.  Which means your body will decide it's got to get rid of that excess urine, and you'll have to go to the bathroom.  
    • That's right, when you've gotten your kid all bundled up like Ralphie's little brother and you've sent him outside, don't be surprised if he runs back in half an hour later, saying he's got to go to the bathroom.  His not trying to be annoying, it's just his body helping him to survive the cold.

Yes, right about now is when he'll have to go to the bathroom.  Thank the cold air for that.
(Screen shot sourced from SpartanTailgate)

  • Sidenote: You might be wondering, how does the nose running fit into all this?  Is that another blood vessel construction/fluid expelling thing at work?  Well, no.  That is just your nose doing its own thing.
  • Your nose's job is to warm, moisten, and filter the air your breathe in so it doesn't hit your lungs all dirty and cold and dry.  Hack, hack, just the idea of that makes me want to cough.  That's what your nose does all the time, courtesy of the nose hairs and mucus in there.  
  • But when it's really cold out, that cold air is also especially dry.  So your nose has to work extra hard to add more moisture to that air to keep everything nicely humidified for you.  Then, when you exhale through your nose, that extra moisture is going to get pushed back out toward the end of your nose, which because of the cold outside is getting a little chilly.  The cooler temperature at the end of your nose will make the moisture condense there, and so you get a runny nose. 

[I don't think you really want to see a picture of a runny nose, so we'll pass on this image opportunity.]

  • OK, so we've got blood vessel constriction and blood vessel dilation going on, with maybe a need to urinate more frequently and perhaps a runny nose thrown in for good measure.  Now, if I go inside, all those anti-cold-weather reactions will settle down and relax in the warmer inside air.  But the key is, over the course of a couple of weeks' worth of going outside to the cold and coming back in, your body gets better and better at managing that trade-off between constriction and dilation.  So when you go outside, your body is already kind of prepared to go into cold-weather-response mode.  You don't feel the cold as much on Week 2 as your did on Week 1.
  • "Physically, you never get used to the cold. It's cold! If it's cold, it's cold! And you go out there and your body feels it, but I think mentally, living in it, it's not such a shock to you. I took the dog out last night, it was 20-something degrees and I'm like, 'Yeah, I'm in my shorts, but I did this the day before, and the day before …'"

Clay Matthews takes his dog out in 20-degree weather while wearing his shorts.  I think that means his body has gotten used to cold weather.
(AP Photo from the Courier-Journal)

  • After a very long time of being exposed to very cold temperatures, you body will also change its rate of metabolism--that is, the process by which your body converts food into energy.  This is something that happens to deep-sea pearl divers, or to researchers who stay in the Arctic for a year or more.  But after that amount of time having been exposed to such cold temperatures, their bodies will speed up metabolism in order to generate more heat.  So after several months of this hardy-cold living, they will be able to tolerate diving in 50 degree water without a wet suit, or walking around the Arctic camp in T-shirts.
  • For the rest of us who merely have to adjust to the change in seasons in more moderate climates, there are some things we can do to help our bodies make the transition:
    • Layer your clothes -- For example, wear a warm sweater over a short-sleeve shirt over a long-sleeve shirt.  The extra layers will help your body when it first encounters the cold -- and believe me, it will know it's cold out from the cold air that hits your face.  Once your body's made its adjustments and is warming up, you can open your coat or take off a layer.
    • Stay hydrated -- even though your body will try to respond to the higher pressure by getting rid of excess fluid, everything will work better with moisture.  Especially if you are exercising (e.g. running) in the cold, you'll want to keep hydrated so your nose can continue its essential humidifying activities and so you can keep your muscles from cramping.
    • Take off your cold clothes when you get inside -- cold air will be trapped in your clothes, though you may not have noticed that while your extremities weren't getting much blood flow.  But once you get back inside where it's warmer, your body will try to warm up those fingertips and ankles and feet again, and it will also realize, hey, I've got to try to fight against the cold air stuck in the pants cuffs and sock wrinkles and whatnot.  Do your body a favor and shuck off all those cold clothes when you get inside and change into snuggly warm things.
    • If you want to try to speed up your body's acclimation to winter weather, you could try taking cool showers or cool baths.  Many people say this does help speed up your body's response mechanisms to cold weather, so you become better-acclimated sooner.  Do not immediately plunge your body into a bathtub full of ice and sit there for 15 minutes.  Also do not try this if you have an existing hearth condition.  Be judicious about this.  Take a cool shower for 5 minutes, get out, towel off thoroughly, and warm up.  Remember, your goal is to speed up the process, emphasis on that word process.  Your body is not a light switch that turns off and on suddenly, but rather a serious of interconnected mechanisms that work best when they work together.  You want to help your body, not punish it.

Once you've done all that, then have a cup of hot chocolate. Specially recommended by your Apple Lady!

Emily Sohn, Cold Weather's Coming: Is Your Body Ready? Discovery News, September 19, 2013
Cool Antarctica, How humans deal with and survive extreme cold
Laura McMullen, 6 rules for working out in cold weather, NY Daily News, December 5, 2013
Mich Smith and Lolly Bowean, As winter wears on, bodies adjust to the chill, scientists say, Chicago Tribune, February 8, 2014
Medicine.Net, Goose Bumps
NPR, Why Does Cold Weather Cause Runny Noses? January 24, 2009
Cold Showers, Ice Bath Benefits and Considerations

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