How your thirst gets quenched

Being dehydrated means not having enough water in your blood. If this happens, you get thirsty and you go for a drink, after which you’re not thirsty any more. But wait a minute! It takes ten or fifteen minutes for the water to make its way into your bloodstream. You certainly don’t continue gulping water for ten minutes waiting for your thirst to be quenched. So what stops you from continuing to drink water—which can actually be dangerous?

If we’re like mice, on whom new research was conducted, we have cells in our brains that regulate thirst. But those cells don’t respond to the water itself. They respond to the speed at which the water is ingested—that is, the gulps. In the mice, feeding them water-saturated gel or giving them sips didn’t stimulate those cells. They would continue to drink even when they’d had enough. They needed those big swallows to quench their thirst.

Regulating water in this way was surely an evolutionary benefit. Drinking too much water dilutes the blood, which throws off the sodium balance, which causes cells to swell. (The condition is called hyponatremia.) If the swelling occurs in the brain, you can die, as happened to several football players who overdid it (as I mentioned in an earlier post).

Because your gut has a brain of its own, it probably has similar sensors, but the scientists haven’t figured out that one. In the meantime, enjoy those big gulps.

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