Why does being hydrated make you sleep warmer?

"…properly hydrated…"

In high intensity performance a 2% deficiency in hydration results in something like a 10% + decrease in output. Laying there in your sleeping bag isn't very demanding, but I would assume a similarity.

Being low on fluids impairs metabolism.
Low metabolism means low heat.

Just a wild a$$ guess.

Not quite sure why I didn't think about that. Did a quick search on how hydration affects your metabolism and makes sense that it would lower your body heat output if your metabolism is lower.

Thanks for the clarification!

I am not sure that it is quite that simple.

You do need water to aid in digestion, and digestion is what provides all the warmth in your body. However, I doubt that ordinary thirst would make much difference when you are lying down (exercising may be different). There's an awful lot of water in your body even when you are thirsty.

I suggest that a significant effect is that when you are thirsty you just can't relax as well. So you stay awake and squirm around and that makes you get cold.

But, this is just a thought, based on how people get cold when they are trying not to go to the loo at 2 am. There may well be physiological factors I don't know about.

Cheers

No question about how something works is a stupid question, but this one is especially not stupid – darn good question!

I suspect that under most relevant conditions, it's the effect of dehydration on blood flow to your skin and extremities that makes you feel colder when you're a little dehydrated. Looks like there's a study showing this, available at http://www.dtic.mil/dtic/tr/fulltext/u2/a130838.pdf .

Best,

Bill S.