Jul 23, 2019 | Updated: 09:13 AM EDT

Thirst: How the Body Regulates It

Mar 28, 2019 10:32 AM EDT

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Ever notice how an ice-cold glass of water can be the most delicious and refreshing option at times, while other times it feels as if your body is just saying no? A new study conducted in mice suggests that a mysterious element in the stomach may play a role by predicting how much you need to drink to satisfy the body. It then promptly notifies the brain, which, in turn, decides how thirsty to make you, a group of researchers recently reported.

In 2016, a group of researchers at the University of California, San Francisco found that when mice drink liquids, it prompts the mouth and throat to send signals to the brain, which shuts down the brain cells that dictate thirst. These "thirst cells" are found in a region called the hypothalamus, which regulates thirst, blood pressure and other bodily processes, and also in a small neighboring spot called the subfornical organ. However, when they gave the mice salt water, the scientists found that the thirst neurons stopped firing almost immediately, as expected.

"Somehow, the brain has a way to match these two different timescales so that you can very rapidly drink just the right amount of water to satisfy your body's needs," said study author Zachary Knight, an associate professor of physiology at UCSF and a Howard Hughes Medical Institute investigator.

The findings, if confirmed in humans, could benefit a range of people. For example, Knight noted that our ability to regulate thirst decreases with age. "So [elderly people] fail to stay properly hydrated, and that can cause medical problems, especially, during times of intense heat," he said.

The team also found that the thirst signals traveled along the main signal highway between the brain and the gut: the vagus nerve. When the researchers cut out this nerve in a later experiment, the thirst neurons didn't turn back on when the mice started drinking. Though they don't know for sure, the team thinks that the signals are coming specifically from the small intestine, which is the spot that connects most strongly to the vagus nerve and is also in the "correct" timespot in the digestive process to activate those thirst nerves a minute or so after drinking water.

Keeping these recent developments in mind, we should always pay close attention to the amount of water we drink. Recent statistics show that 75 percent of Americans are dehydrated and that most Americans are considered chronically dehydrated. On the other hand, consuming too much water could possibly lead to hyponatremia or 'overhydration', which can be fatal as well.

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