Should You Pee When You’re Cold?

I felt cold yesterday while out at the Field School. It was a different kind of cold from today’s cold, wetter, less biting, but cold nonetheless. We were talking with the kids about ways to stay warm in the cold, and one of the suggestions that came up was that peeing would help you stay warm. This made me curious about the relationship between pee and cold weather and other creative ways I might be able to stay warm. 

When I moved to Vermont, I noticed rather quickly into my first winter just how frequently I had to pee whenever the temperatures dropped into the 40s (a phenomenon called cold diuresis). I don’t drink all that much as it is, but on a cold day I would drink to stay hydrated from the cold, dry winds, and I always seemed to pee out more than I took in. I also noticed how different my sensory experience of the world is during the winter as compared to the summer. And it turns out there’s a cool (pun intended) reason for all of this. And it mostly has to do with our blood.

As temperatures drop, our sensory experience of the world changes, altering the way that we perceive the world around us.

• Smell: Cold air seems to have its own particular scent. This is in part because there’s less to smell in cold dry air, but also because our olfactory receptors retract, which reduces the likelihood they’ll be able to detect any odors.
• Taste: While external temperature doesn’t have much impact on the temperature of our mouths, the temperature of food greatly impacts how that food tastes. Generally, colder food is harder to taste (probably why Coors wants you to drink their beer ice cold). As bitter beer tastes more bitter in warm weather, so too will your ice cream taste sweeter as it warms. This works up to a certain point, but too hot and bitter flavors become muted. Hence hot teas and coffee.
• Sound: Sound travels farther (but slower) in cold air. The lack of leaves on our hardwoods also allows sound to travel much farther through a forest. And while the connection isn’t entirely clear, people are more likely to Google “tinnitus” during the winter than during warmer months (source). Ear wax production also increases in the winter, so you might not be able to hear as much of that crisp winter sound.
• Touch: Your hands may pale as blood flow decreases and skin temperature can be significantly lower than your internal temperature. As your skin temperature drops, so too does your ability to perceive pressure. This is partly why it can be so tough to tie knots when your fingers are cold.

Part of the reason the sharpness of your senses declines is because cold weather prompts your body to shunt blood away from your extremities and towards your core. It’s more critical to maintain a constant temperature your where all your vitals are than in your finger tips. This deprives our cold extremities of oxygen, slows the firing of our neurons, and cripples proteins.

As the capillaries in our hands and feet constrict and blood concentrates in our core, this raises our blood pressure. The increase in blood volume is handle by the kidneys, which kick into action, filtering out water and ultimately increasing the amount of urine produced. Pretty neat.

There are a few other, more mundane reasons we pee more. We’re less active, and when we are active it tends to be colder out, both of which mean that we sweat less during the day. Since we sweat less in cold weather, our body needs to find other means of offloading all that extra water. And since we’re not out hiking, biking, and spending time outdoors, we have easier and more constant access to water. Additionally, the cold dry weather also dries out our skin, which triggers a thirst response. Drink more, pee more.

Also of note is that we excrete more calcium in the winter than in the summer (source). Combine this with lower rates of exercise, weight gain, and a more salty/processed food diet, and we find ourselves at a higher risk of getting kidney stones in the winter.

Okay, so you’re cold, you have to pee, your senses are all wonky, and you want to be warm. What do you do? Well, there are two ways of thinking about this question. The first is that you can just be warmer (or at least buffer yourself from the cold). Think here: wear warmer clothes, shelter from the wind, do jumping jacks, etc.

The second way is to go back in time and alter your physiological response to the cold through training. It’s no surprise that exposure to cold weather changes your perception of what’s cold. I’m more comfortable running in shorts and a t-shirt on a 45 degree day in March than I am in October. And speaking of running, endurance training also enhances your ability to withstand pain, including the discomfort associated with being cold (endurance athletes can hold their hands submerged in ice-cold water for significantly longer than your average person). Repeatedly spending time in the cold followed by warming up can condition your brain to the idea that the cold is not as shocking of a threat to your longevity as it initially may have thought. This habituation to the cold results in three main changes to how your body responds to cold temperatures: (1) your skin temperature remains higher (because your capillaries only constrict at lower temperatures), (2) you delay activating your shiver response for a longer period of time, and (3) your sensation of cold is dulled (source).

Alright, so we still haven’t quite tackled yet whether or not you should pee when you’re cold. The consensus seems to be that since urine is stored in your core and you have to spend precious calories keeping your core at a constant temperature, peeing would relieve your body of the caloric burden of keeping your urine warm.

But I’m not convinced, and it doesn’t help the “pee” camp’s case that many of these resources will also tell you to sleep with a bottle of warm water in your sleeping bag to stay warm at night. I actually think that peeing might cool you down and make it harder to stay warm. So here’s my case: the pee is already at the same temperature as your body so you don’t have to heat it up. Water is particularly tough to both heat up and cool down (this is called heat capacity, and water has a higher heat capacity than say fat). Therefore, maintaining urine at a constant temperature isn’t as energy intensive as the surrounding tissue. The urine adds volume to your body, making it more difficult for the cold environment to sap away your heat. Here a full bladder might act in a similar way to a large lake next to a city that helps keep the temperature of the land (which has a lower heat capacity than water) relatively stable.

Also, in order to pee you would need to shed layers and expose some skin. After peeing, you’d then need to use heat from your body to warm up all that cold air that got trapped in your layers. So the question is whether the energy to keep your urine at your body’s temperature is greater or less than the energy it takes to warm yourself up after peeing. And unfortunately it doesn’t look like there’s any scientific literature on the subject. It’s also not lost on me that you need to consider here the tremendous discomfort of having to hold your pee in the cold.