According to a study published in the journal Nature by McGill University researchers, the brain’s biological clock stimulates thirst in the hours before sleep.
The research was conducted on mice. Scientists knew that rodents show a surge in water intake during the last two hours before sleep. The study revealed that this behaviour is not motivated by any physiological reason, such as dehydration. So if they don’t need to drink water, why do they?
The research found that restricting the access of mice to water during the surge period resulted in significant dehydration towards the end of the sleep cycle. So the increase in water intake before sleep is a preemptive strike that guards against dehydration and serves to keep the animal healthy and properly hydrated.
“Although this study was performed in rodents, it points toward an explanation as to why we often experience thirst and ingest liquids such as water or milk before bedtime,” Bourque says. “More importantly, this advance in our understanding of how the clock executes a circadian rhythm has applications in situations such as jet lag and shift work. All our organs follow a circadian rhythm, which helps optimize how they function. Shift work forces people out of their natural rhythms, which can have repercussions on health. Knowing how the clock works gives us more potential to actually do something about it.”
In essence, you don’t really feel thirst before sleep because you are thirsty; it’s only your brain sending thirst signals to take precaution.