Dear Sasquatch: Do we sweat a liter of water at night?
My mom insists that I keep a glass of water by the bed each night to drink when I wake up, to avoid dehydration. She says that we lose a liter of water a night just through sweating. Is this true?
How much water we lose when we sweat at night varies quite a bit depending on the temperature of the room, how many blankets we use, whether we have any health issues or are taking particular medications, just to give a few examples. And we all vary in how many sweat glands we have, anywhere from 2 to 4 million. That’s a lot of variation!
Anytime various factors affect an outcome, it is a good idea to be skeptical, as you are, of any one-size-fits-all figure. And in this case, a liter is a lot of water to lose through perspiration for anyone. I found a range of figures when looking up how much water the average person loses in a day through sweating, but the range was still less than a liter (500 to 750 milliliters, not taking exercise into account).If you are sleeping in really high temperatures or high humidity, you could lose that much or even more, and if you have hyperhidrosis, the name for the condition of excessive sweating, or are experiencing night sweats, you could lose that much.
Other possible reasons for excessive night sweating are, as I mentioned, medications (such as certain antidepressants and even acetaminophen or aspirin), menopause (probably not an issue for you), anxiety problems (particularly panic attacks), and various infections and diseases. In most cases, these will cause you to sweat a lot more during the day as well, so if you are experiencing what seems like more sweating than normal, get checked out. Even if doctors can’t figure out the cause, they can treat the problem in various ways.
But I’m guessing from your question that you aren’t having a particular sweating issue, in which case the glass of water really isn’t necessary, although I doubt it does any harm just sitting there or if you drink it first thing in the morning.
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Image credit: Adapted from original photo by James Yu.