Thirsty before sleep?

21 Oct Thirsty before sleep?

Do you often find yourself feeling thirsty just before bedtime? Have a routine of sipping on a glass of water as you trotter off to bed to leave on the bedside table? Or are you the type of person, despite the urge, who refuses to drink anything before bed to avoid that annoying trip to the toilet during the night…..

I must admit, I have a habitual routine of taking at least 10 sips of water before bed, regardless of whether I’m thirsty or not.  But why do we feel this need for a drink despite sometimes not even being thirsty, or is it just a habit to have a glass of water beside the bed?

Well, believe it or not, scientists have just revealed that your brain’s biological clock stimulates thirst neurons to give you that thirsty urge before bedtime, regardless of any need for hydration. Think of it this way, your body is wired to make a pre-emptive strike to guard against dehydration while you’re sleeping.

The study published in the journal Nature found that when the scientists deprived mice of water in the two hour period prior to sleep it resulted in significant dehydration towards the end of the sleep cycle. It provides the first insight into how our body clock regulates a physiological function. Although the early stages of research are on rodents, the findings could point the way toward drugs that could help negate problems that people experience from shift work or jet lag, by better understanding how our ‘body clock’ executes a circadian rhythm.

So, what mechanism did the scientists find that sets this thirsty urge before bed into motion? And do we really have ‘thirst’ neurons?..

It’s actually well known that the brain harbors a hydration sensor with thirst neurons in that sensor organ. So the researchers wondered if the SCN, the brain region that regulates circadian cycles, ‘the biological clock’, could be communicating with these thirst neurons.

The team suspected that vasopressin, a neuropeptide produced by the SCN, might play a critical role. To confirm that, they used so-called “sniffer cells” designed to fluoresce in the presence of vasopressin. When they applied these cells to rodent brain tissue and then electrically stimulated the SCN, they saw a big increase in the output of the sniffer cells, indicating that vasopressin is being released in that area as a result of stimulating the clock.

To explore if vasopressin was stimulating thirst neurons, the researchers employed optogenetics, a cutting-edge technique that uses laser light to turn neurons on or off. Using genetically engineered mice whose vasopressin neurons contain a light activated molecule, the researchers were able to show that vasopressin does, indeed, turn on thirst neurons.

So, the research certainly points toward an explanation as to why we often experience thirst leading up to bed. Perhaps if you are the type of person to refuse yourself a drink before bed, maybe think twice and give in to the urge.


Reference and story source:

  1. Gizowski, C. Zaelzer, C. W. Bourque. Clock-driven vasopressin neurotransmission mediates anticipatory thirst prior to sleep. Nature, 2016; 537 (7622): 685 DOI: 10.1038/nature19756