Why you are not thirsty while sleeping

March 2, 2010 by Lin Edwards report
A child sleeping (Sleep)
A child sleeping. Image: Alessandro Zangrilli, via Wikipedia.

(PhysOrg.com) -- New research suggests the body's internal clock is what prevents you from becoming dehydrated and needing to drink during sleep.

The research was carried out by neurophysiologists Charles Bourque and Eric Trudel of McGill University Health Center’s Research Institute in Montreal, Canada. The study identified how the body’s internal clock (circadian system) controls water regulation during sleep through activating the release of the hormone , which instructs cells to retain water.

During waking hours, the body controls hydration by balancing the loss of water via urine with intake of water by drinking, but people do not drink or go to the toilet while they are sleeping, and so the body must use another mechanism to keep itself hydrated. Research has already shown that body clock declines and vasopressin levels are raised when we are sleep, and that vasopressin is released by specialized neurons, which are activated by osmosensory neurons when water levels are low.

Bourque and Trudel’s research investigated the proposal that reduced activity in the clock neurons could enable the osmosensory neurons to activate neurons to release vasopressin before water levels were low, which would lead to lower levels of urine production and greater water retention. They achieved this by removing thin slices of rat brains with intact clock and vasopressin neurons. The neurons function even when isolated from the brain. They stimulated the sensory neurons and monitored between them and the neurons producing vasopressin, and compared the communication between the neurons when the clock neurons were activated (the ‘awake’ cycle), and when they were not (‘’ cycle). They found the communication between sensory and vasopressin neurons decreased significantly when the clock cells were activated.

In essence, the body clock neurons act as a kind of ‘dimmer switch’, so that when they are active they suppress instructions to discharge vasopressin, but when they are inactive the can more easily instruct the neurons to release vasopressin, which ensures the retain their water reserves.

Rats and humans have similar vasopressin and body clock neuron activities, but Bourque said more research is needed to determine if the neurons regulate other cycles as well, such as sleepiness, hunger, and other mechanisms related to circadian rhythms.

The research paper was published in the journal Nature Neuroscience.

More information: Trudel, E., Bourque, C. W. Nature Neuroscience (2010) doi:10.1038/nn.2503

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5 / 5 (1) Mar 02, 2010
But I don't get it. Often I wake up in the middle of the night and need to have a drink.
not rated yet Mar 02, 2010
This is a general property for healthy people in low load environments. The body has to adapt to different environments if you are to survive so that will effect this system and other backup systems to generate different behaviors. The environment also includes your own body.

I have an inflamed prostate and have to wake at least once a night to urinate. I also take antidepressants that have side effects of reducing saliva production. I often drink water during the waking urination cycle.

You might have your own environmental influences, maybe you have a hidden sugar regulation problem or maybe your bedroom is too dry.
5 / 5 (1) Mar 02, 2010
I definitely get thirsty while sleeping. Then wake up and drink.
I may do a equally valid study - why don't you feel you need to urinate whilst peeing.
not rated yet Mar 02, 2010
This is a really odd study because I remember reading another study concerning how to get a good night's sleep. According to that study, some people wake up and have a hard time going back to sleep because their body needs water but the thirst alert system is partially shut down. Therefore, it recommended getting a drink of water whenever one woke up in the middle of the night. I tried it and it worked miracles. Now I always keep a glass of water on the night table. Yet this article says almost the exact opposite. Well, I'm sticking to the glass of water method!

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