If you’ve ever run a marathon, half-marathon, or any other long race, you’ve undoubtedly had a hydration plan: a detailed assessment of what you intend to drink, when you intend to drink it, and how you intend to obtain it. But a paper in tomorrow’s issue of Science may cause you to rethink exactly how you do this, suggesting that to a larger degree than people have thought, you may be able to trust your sense of thirst to tell you when you are and aren’t getting enough fluids.
Not all that long ago, runners were told that thirst was a “slow” reflex that lagged well behind the body’s actual needs. But it actually appears to be exquisitely sensitive, integrating an amazing amount of information in real time, says Christopher Zimmerman, a neuroscientist at Princeton University, Princeton, NJ, who won the Science magazine’s 2020 Eppendorf prize for his work in the field.
A Sophisticated Thirst Sensor
Decades ago, Zimmerman says, researchers realized that the sense of thirst was regulated by a tiny part of the brain called the subfornical organ (SFO), about the size of a grain of rice, buried deep within the brain.
What made it interesting, he says, is that it was located outside of the blood-brain barrier, the membrane that separates the brain from the bloodstream, insulating the brain from toxins and pathogens that might be in the bloodstream. Being outside that barrier allowed it to monitor the blood for important changes related to hydration, such as the “osmolarity,” or salt and protein content, of the blood.
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