Why you don't need 8 glasses of water a day | Body Stuff with Dr. Jen Gunter | TED

Transcriber:

You know that whole thing about drinking eight glasses of water a day?

Sorry to have to tell you this, but it's a myth.

It won't make your skin brighter,

it won't make you feel clearheaded,

it won't make you feel more energetic.

It might, however, make you have to pee a lot.

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[Body Stuff with Dr. Jen Gunter]

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Many people don't understand the biology behind their bodies.

There's a lot of misinformation out there.

But the truth is that when you understand how your systems function,

you're able to make better decisions.

You're not as prone to fall for hype or pseudoscience.

You'll feel empowered to understand what's really going on.

One myth that really bugs me

is the idea that you need eight glasses of water a day.

Honestly, it's pretty shocking how ingrained it is.

You hear it on TV, you see it in articles.

But like I said, it's nonsense.

For the most part,

your body will tell you when you need to drink water,

because you've got these wonderful, amazing, undervalued things --

kidneys.

Kidneys are the bean-shaped organs located to either side of your spine,

right below your ribs.

They're often thought of as a filter or a waste-removal system,

but that doesn't do the kidneys justice.

Your body is an environment where everything, fluid and chemicals,

needs to be in a delicate balance.

The kidneys do a lot of the heavy lifting when it comes to this balance.

Every day, blood in your body passes through the kidneys.

What you eat, drink, the temperature around you,

how much you exercise --

all of this affects what's going on with your body.

Your kidneys, along with your nervous system and various hormones,

are constantly watching many gauges

and making adjustments about fluid, salt and levels of other substances

in real time.

They do this with about one million tiny structures called nephrons.

These nephrons are kind of like workers on a conveyor belt,

actively adding things and taking things away,

things like sodium, glucose or sugar, calcium, amino acids and water,

to make sure the body maintains homeostasis, or balance.

If levels of anything get too high or too low,

then that can be harmful.

And it is the job of the kidneys

to keep the levels of many of these substances in the just-right zone.

Substances that aren't needed leave the kidney

and head to the bladder,

where you excrete them in the form of urine.

So where do eight glasses of water a day fit in?

They don't.

Noticed that I did not say

that the kidney function is improved with excess water.

Imagine that you're sweating a lot,

so you're losing water from your blood.

The kidneys know your blood volume is dropping ever so slightly

and that your blood is getting ever so slightly saltier.

They compensate by absorbing more water back into the blood,

making the urine more concentrated.

If the kidneys sense enough fluid can't be reabsorbed from the urine,

you're signaled to drink, meaning you get thirsty.

If you don't have fluid available,

the thirst message gets stronger and stronger.

A person facing real dehydration won't be unsure if they need water.

They'll do whatever they need to get it.

It's one of our most basic instincts

that's evolved over a very long time,

in environments where clean water

wasn't nearly as readily available as it is today.

So thanks to your kidneys,

your body is really good at maintaining hydration.

But if you stop counting eight glasses of water a day,

how much should you be drinking?

The answer is simple:

there is no should.

When you feel thirsty, drink some water.

You can trust your body.

Unless you have kidney stones or are elderly --

sometimes, our messaging systems get a little worn with age --

or your doctor has told you otherwise,

constantly monitoring how much water you drink

is not really necessary.

Here's a point that's often missed:

every single thing you consume contains water.

Your morning coffee has water, so does your breakfast.

And that snack -- an apple, an orange, a glass of juice, a granola bar --

just like you, they're made of water too.

So as long as you're listening to your body's internal sense of thirst,

there's really no need to be counting those eight glasses.