Does thirst mean you’re already dehydrated?

Imagine if this were generally true. You’d see billboards declaring “Not thirsty? Better have a drink anyway”. Neurotic parents would hook their obscurely-named children up to intravenous drips. And rather than scoffing at people who carry a water bottle at all times to keep themselves topped up, we’d all be doing it too. But it isn’t true, in general or at all.

Sports scientists did at one point think it true during exercise. Dehydration incurs a huge penalty during exercise so a lot of research goes into making sure athletes are properly diluted at all times. It used to be thought that thirst didn’t kick in soon enough to replace the weight of water lost during exercise, and it still is, but more recently it has been found that the body adjusts to cope with some water loss during activity without actually becoming dehydrated.

But it takes time for the latest research to filter from the lab through scientific publications to the public. Professional know-alls like myself have to stay on top of these developments. The printed word provides us with a stately cloak of authority — one which would wear quite thin if you saw how we dress or the state of our refrigerators — and we wouldn’t want to abuse that by giving out misleading information.

Don’t worry, though, because I’m right up on the play with this. All the evidence indicates that thirst is a precursor to dehydration, not a result of it, whether at rest or play. Thirst kicks in when hydration levels drop just slightly, well before any problems develop. Anticipating a further drop the body tries to head off dehydration before it happens. And most of the time it succeeds.

It really makes sense that thirst precedes dehydration — the other way round would seem to be a pretty flawed design, given how important water is for our survival. Anyway, I think that’s enough pontificating for the time being. You can’t wear this cloak of authority long without working up a thirst, especially in the warm weather. I’m off for a drink.

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