How much water do you actually need a day?: Transcript

Body Stuff with Dr. Jen Gunter

Wednesday, May 19, 2021

JEN GUNTER: I’m Dr. Jen Gunter. I love science, and I hate when people twist it. And there's a lot of twisted medical misinformation out there.

"That’s ridiculous."

"Oh It’s so painful."

JEN GUNTER: We’re exposed to medical myths whether we are looking for them or not. There are news stories, Instagram and Facebook posts flying past 24/7 , TikTok, Twitter. Who has valid information and who’s just trying to sell you something? How do you sort the medicine from the mayhem?

I’m Dr. Jen Gunter, and I’m here to help. From the TED Audio Collective, This is Body Stuff.

I’m a doctor - a practicing gynecologist - and I've made it my mission to give women the facts that they need to understand their bodies. In my 25 years of talking with patients, I’ve learned that medical misinformation is a problem for everyone. And every single one of us is susceptible.

So this show is about debunking some of the STICKIEST myths out there… while helping you understand how your body really works.

Today… why you DON’T need eight glasses of water every day.

We’re going back in time to find the origins of that myth... and then we’re going to meet a kidney expert
who’s going to illuminate just how hard our bodies work for us
to maintain our hydration.

DR. TOPF: People, It’s like an exquisitely designed atomic balance machine, okay? You have to keep everything in balance..

JEN GUNTER: But first, I want to tell you about something that happened to me when I was ten years old. It was a time in my life when I got asked a lot about my urine… and it ended up setting me on a path to becoming a doctor.

It was the first good weekend of spring 1977 in Winnipeg, Manitoba. The kind where the sun feels hot and you're just raring to get outside. I was messing around with my brother's skateboard going down the street and then all of a sudden I was flat on my back, on the concrete, and I was in a terrible amount of pain. It felt like my insides were on fire.

The next day, I'm sure I didn't look well. So we went to the pediatrician who took one look at me and called a general surgeon, who took one look at me and sent us to the emergency department. They gave me something called an angiogram. And I remember the doctor pointing to the x-ray screen explaining what he was seeing, and of course it just looked like a snow storm to me.

And that's when I learned that when I fell off my skateboard, I’d ruptured my spleen. The good news was I wasn't going to need surgery, but there was something else. It looked like i had hydronephrosis - my kidney was full of fluid. And I needed to see a pediatric urologist. He sat us down in his consultation room and started to explain to my mom what needed to happen. And I could tell that she was confused. I think the doctor could tell as well… so he gestured to me and he said, Hey, you come over here. This is your body. You should know how it works.

So I came over and I sat down, I traded places with my mom, and he drew a little diagram and he explained how the kidney works and what he thought was wrong and the tests that I was going to have to have and the surgery that I was probably going to have to have as well. When that doctor took the time to explain my body to me, it really helped me not feel scared or overwhelmed.. and that experience made me decide I wanted to be a doctor. I loved the science and I wanted to be able to give to my patients what that doctor gave me that day. That empowerment of knowing how your body works and how to use that knowledge to help improve your health.

Eventually I did have a surgery to remove my left kidney. I lived most of my life with just one kidney... the organ that's largely responsible for regulating our body’s hydration. But you want to know something? None of my doctors ever told me to worry about how much water I was drinking.

I graduated from medical school when I was 23 so I've been a doctor more than half my life. And I've seen first-hand the problems that happen when people get misconceptions about their health. And a lot of those misconceptions, they start with the internet.

I'm not one of those doctors who rolls her eyes when her patient comes in with reams of advice from Dr Google. That tells me my patient is engaged, she wants to learn. But there are a lot of bogus recommendations out there. And often they’re being pushed by brands and influencers. A lot of them sound like they make sense… in a sort of science-ish way — like the eight glasses of water a day thing. We’re made of water, so why wouldn’t we need lots of water? But that’s not science.

So what's behind this myth? How did we get to eight glasses of water a day anyway?

There are a couple of potential origin stories. One is a paper from 1945 that suggests the body uses about 84 ounces of water a day, and there's another paper from 1974 from a pair of nutritionists who recommended an equivalent of six to eight glasses of water a day for the body to function appropriately. But these papers became distorted over time, like a bad game of telephone.

These experts weren't recommending that we drink six to eight glasses of water a day on top of everything else. They were saying this is the amount of water the body needs to function. But that water doesn’t have to be water you drink from a glass out of your tap… water is in everything.

Think about a breastfed baby - all they’re drinking is milk. The body is able to remove the water from the milk, so the baby never gets dehydrated.

In the same way, once we start eating solid food, our bodies continue to extract water from everything we consume.

Everything we eat or drink counts. So the water in your apple counts, the water that's in the bread that you eat counts, even coffee counts. Any fluid counts.

Look, I get this is a real record-scratch freeze frame moment for a lot of people - but we don’t just get the water we need from plain water. And if you have one of those days where you just drink coffee all morning, and you don’t feel great - maybe you’re a little headachy or a little jittery - it’s not because you’re dehydrated. Maybe you had a little too much coffee, or you had it on an empty stomach.

If you like drinking six glasses, eight glasses of water a day, and your doctor hasn’t advised against it, that’s probably fine! What I'm saying is that there's nothing medical about this number. We get to make choices about what we put in our body, and this is one of those choices. If you think about it, just using common sense and putting the medicine aside... Does it seem realistic that we evolved needing to consume that much clean water every single day? In the span of human history, access to clean, plentiful drinking water is a relatively recent phenomenon.

And even today in many parts of the world, accessing clean drinking water isn't as easy as walking into your kitchen and filling up a glass. It seems unlikely that our ancestors carried giant water bottles around with them at all times.

And yet the 8 glasses of water a day myth spread and spread and spread. But why is this myth so sticky? It turns out there's a mix of factors, including a little bit of intrigue and one particular culprit that deserves a lot of the blame: the beverage industry.

Fake beverage commercials:
“Sometimes water just isn’t enough.”
“Dry mouth? Time to refuel” “Unquenched thirst has become a chronic problem in America”

DEB COHEN: If you're going to sell something, you've got to have a reason to sell it. You have to create a market for it. You have to create a need.

Fake beverage commercials:
“Water just isn’t enough.”
“Quench your thirst”

DEB COHEN: It's things like "pre-hydrate." I mean what does that mean? Drink ahead of your thirst. Train your gut to tolerate more fluid. Your brain doesn't know when you are thirsty.

JEN GUNTER: Dr. Deb Cohen went to medical school in the UK, but instead of becoming a clinician - a doctor who sees patients - she became a journalist. Back in 2012, during the lead up to the London Olympics, she was the investigative editor at the British Medical Journal.

She wrote a report called “The Truth about Sports Drinks.” And it set off a bomb in the beverage industry. The report looked at the history of sports drinks like Gatorade, and how their advertising basically invented the modern fear of dehydration.

DEB COHEN: It was really in the kind of the boom of the marathon era in the 1970s that sports drinks really took off. It started life in Florida at the University of Florida. And Robert Cade was the renal physician and he'd developed this drink for the, for the Gators football team.

And it was effectively water, um, sugar, um, dash of sodium, and a bit of lemon juice. So quite simple. And it was supposed to help alleviate cramps. And then it was bought up by, um, Quaker Oats and they spotted a big market. And that's really where the science of dehydration started.

JEN GUNTER: Ok, so we’re not talking about clinical dehydration, which is a real condition. For example, the time I had food poisoning and I was up all night vomiting, so I had to go to the emergency department and get an intravenous.

DEB COHEN: But, but this is healthy people. So this is a whole different phenomenon. And so what they turned into an illness was exercise-induced dehydration.

JEN GUNTER: Exercise-induced dehydration.

DEB COHEN: Now that sounds a lot more important than you're a bit thirsty if you've been running and sweating. If you tell people that it's, it's all about the science, then then people are more likely to believe it.

JEN GUNTER: Beverage companies, especially Gatorade, commissioned studies looking for results that would bolster their sales pitches. By the time Dr. Cohen started looking into these studies, there were a lot of them. GlaxoSmithKline, at the time the company behind a popular British sports drink called Lucozade, claimed they had more than 100 clinical trials. That’s a lot of studies.

And the studies were a little bit… off.

DEB COHEN: Some of the studies we were actually having a bit of a laugh about, um. So what you would do is you would starve people overnight. Um, you'd fast them overnight and then you'd ask them to cycle to exhaustion. One group, you would give a sports drink containing sugar, and the other group you would give water. Well, guess what? The people that have had a bit of sugar are going to outperform the people that have been starved and had water, it's not rocket science.

So there are all sorts of these, all sorts of these kinds of studies that they do, and you look at it and go, that just does not happen.

JEN GUNTER: And it doesn't matter that it's not clinically relevant. Now you've got something that looks statistically different and you can peg a marketing campaign around that.

DEB COHEN: Exactly. And if you throw enough darts at a dartboard, if you've got your eyes blindfolded, then one of them is going to hit the dart board at some point.

JEN GUNTER: The studies were junk. But the science-ish conclusions they made began to spread. Especially this idea that we couldn’t rely on our own bodies to tell us when we were thirsty. One of Gatorade’s scientists even said, in 2008, and I quote: “The human thirst mechanism is an inaccurate short-term indicator of fluid needs… Unfortunately, there is no clear physiological signal that dehydration is occurring.”

DEB COHEN: I think even the Mayo Clinic had information that was based on science that had been ultimately derived from the sports drinks industry about when you should hydrate and how you should hydrate. And it even filtered down to influence school guidance in the UK where kids playing soccer would have to go and stop every 15 minutes, 20 minutes to rehydrate, and you'd speak to the teachers and be like, yeah, it's just kids running around, they just need to pee all the time. So kids running off constantly.

JEN GUNTER: Even the US military was in on the quasi-science. In the early eighties, the Pentagon was citing Gatorade Sports Science Institute studies claiming that drinking sports drinks could prevent heat-stroke - a huge concern for soldiers fighting desert wars. But those studies were bunk - there was no evidence that drinking fluids reduced the risk of heat stroke. Even today, the US military remains Gatorade’s biggest customer. Your taxpayer dollars at work.

DEB COHEN: I was warned off several times as well from doing the story. Are you sure you know what you're doing?
And I spoke to people in the U S quite a bit. Sources, and they try to have studies published that were, that were negative and they just could not get them published. And they'd been warned off doing their research as well. And they were saying to me, "do you realize what you're doing here?" And I literally, probably naively just thought, well, phew, sugary water guys. I mean, how, how big a deal is this?

JEN GUNTER: But As Dr. Cohen started her investigation, she began to see there was a lot of money intertwined with the junk science. Sports drink companies spent huge sums sponsoring youth sports, funding sports medicine doctors, and putting their logos on the world’s most beloved teams.

DEB COHEN: And it was like a Holy Grail. You go to, go to sports conferences or sports medicine or sports science conferences. It's displayed everywhere, you know, sponsored and you daren’t criticize the, the sports drink.

JEN GUNTER: So sports drinks have somewhat fallen out of favor since their heyday in the 1980s and 90s. But another product has taken its place, and it's now the #1 selling beverage in the world: Bottled Water.

And Big Bottled Water is very happy to have you believe that you can’t trust your thirst and that you need minimum 8 glasses of water a day.

After the break, we’re going to talk about why this myth just won’t die.


JEN GUNTER: We’re back. Before the break, we learned the origin of the 8 glasses of water a day myth.

We believe myths like this for a lot of reasons, but a big one is something psychologists call The Illusory Truth Effect. When a piece of information is widespread, and you hear it over and over again, you’re more likely to believe that it’s true.

There are a lot of examples, statements like... “We only use 10% of our brains”... or “Eating carrots will help you see in the dark.”... None of these things are true — but I bet you’ve heard them repeated over and over again.

Politicians and marketers take advantage of this all the time. And it works because when you’re assessing whether something you’ve heard is true, you rely on two things. Whether the information makes common sense, and whether it feels familiar.

And research has shown that familiarity can even be more convincing than rationality. Rationality is hard. But remembering if you’ve heard something before? That's easy.

And here's the thing about the illusory truth effect: No one is immune, not even doctors.

DR. JOEL TOPF: There a one day a year in March, we call World Kidney Day, dedicated to improving awareness of kidney disease. And a few years ago, the theme of World Kidney Day was drink a glass of water to help your kidneys, which is just crazy, right? It doesn't make any sense. It's not grounded in science. Um, but you know, it is grounded in, uh, funding for World Kidney Day, which I believe comes from Dannon, a manufacturer of bottled water

JEN GUNTER: You know like the deep state of hydration.


That’s Dr. Joel Topf. He’s a Kidney doctor otherwise known as a “nephrologist.”

I called up Dr. Topf because... what do we do in medicine when we don’t know the answer? We look for an expert. We call a consult. And Dr. Topf is just the chemistry wizard for this job.

DR. JOEL TOPF: I'm a lifelong nerd who's been fascinated by the chemistry of body fluids going on three decades.

JEN GUNTER: I love nerds.

DR. JOEL TOPF: There are an infinite number of fascinating aspects of body physiology or disease states. And one of the truths about medicine is that once you start learning about any one of these conditions, they become more interesting. And back in 1995 when I was a senior in medical school, I, uh, became real interested in fluids and electrolytes. So the precious bodily fluids. The precious bodily fluids. That's right. That's my favorite movie. It's Dr. Strangelove.

JEN GUNTER: Dr Topf knows that the most important thing about precious bodily fluids is that they stay in balance. Which brings us to the tragic case of Jennifer Strange.

DR. JOEL TOPF: So I want you to kind of rewind back to 2007 and the hottest thing in 2007 was the Nintendo Wii. And this radio station got their hands on one and they were running a radio contest. The contest was "Don't wee for a Wii."

JEN GUNTER: The radio station invited eighteen contestants down to their studio to see who could drink the most water without having to pee.

DR. JOEL TOPF: And there was one person who entered, her name was Jennifer Strange, 28 year old mother of three and she ended up drinking two gallons of water in an hour.

JEN GUNTER: That’s a lot of water…. So much water, that a nurse actually called into the station to warn them this was dangerous. You can overload your system with too much water. It can be really unsafe.

DR. JOEL TOPF: As Jennifer left the radio station, she was already complaining of a headache. And what she actually had was a condition called cerebral edema, which happens when you wash your body out from all the critical salts. And when you do this, water will shift from your bloodstream into your brain, cause increased swelling of your brain that cause headaches, nausea, seizures, coma and death. And she ended up dying on her own bathroom floor a couple of hours later.

JEN GUNTER: Jennifer died from a condition called hyponatremia, meaning a dangerously low level of sodium in her blood. She threw off her body’s delicate balance... something we’ve evolved to rely on. It’s called homeostasis.

DR. JOEL TOPF: The body maintains a stable internal environment to provide optimal health for the cells of the body. You can imagine for these cells to grow and to be healthy, they need regulated amounts of sodium, potassium, even things like body temperature needs to be regulated. All these things need to be in an optimal range for growth and health. And that’s an example of homeostasis.

JEN GUNTER: We've evolved to maintain homeostasis through finely tuned mechanisms that sense when things are awry, when we've gone a little bit too far in one direction or a little bit too far in the other. And makes adjustments to return us to our state of balance. Think about the mechanisms that maintain us in homeostasis like autopilots.

DR. JOEL TOPF: I think that's perfect, right? So you can, you, you can think about, um, uh, uh, body temperature is a classic one. Right? So if we get too hot, we start to sweat. Water evaporates from our skin. That lowers our body temperature back down. We get too cold, we shiver, and all that generates heat and brings us back to a normal body temperature. So we have processes that control us from getting too hot and from getting us too cold.

JEN GUNTER: Body temperature is just one example of the autopilots that our body has to maintain homeostasis. And our kidneys - they’re the quarterback of homeostasis. They help to maintain the balance of almost every electrolyte in our body. They help with blood pressure. They’re crucial to maintain PH. And they maintain our level of hydration. One of these autopilots is called osmolality.

DR. JOEL TOPF: Osmolality is just a measure of the total amount of compounds in solution, and so it's analogous to just how salty the soup is. As the osmolality goes up, soup gets more salty. As the osmolality goes down, soup gets more dilute.

JEN GUNTER: In this case, the soup is our blood. To be a little more precise, the fluid part of our blood - our plasma. And the kidney regulates our osmolality so it stays in a healthy range. Jennifer Strange died because she drank so much water that she pushed her osmolality far below the healthy range and her kidneys just couldn’t keep up. Today, hyponatremia is most often seen in athletes who are over hydrating while exercising. Doctors first started seeing it in ultra marathon runners and iron man triathletes in the 1980s... a period of time that nicely coincides with the messaging coming out of the Gatorade Sports Science Institute. And not just extreme athletes. Doctors have seen hyponatremia in high school football players, students in yoga classes, and more. Thankfully, hyponatremia is relatively rare, because of our bodies' amazing ability to defend homeostasis.

JEN GUNTER (to Dr. Topf): I just went for a run this morning. I went for three mile run. and I'm a bit thirsty and a bit hungry. So how's my one kidney, cause I only have one, um, keeping me working right?

DR. JOEL TOPF: So you came back from your run, and presumably during that run, you sweat, you lost a little bit of fluid that way, and that loss of fluid is going to make your body saltier, it's going to make the soup saltier, your osmolality goes up. This is you're pushing your body out of that homeostatic range and it needs to return that osmolarity back down. And the way that it does that is two factors. One, increased thirst, will make you go to the sink, pour yourself a glass of water and drink it.

So in addition to thirst, your kidney is going to respond to that increase in osmolality. And the way it does that is it's going to change the type of urine that you make. You’re always making urine, you’re constantly getting rid of waste products. But one of the variables is how much water is excreted with those waste products.

JEN GUNTER: In other words, if you’re drinking a lot of water, you’re going to pee more! But that doesn’t mean you’re getting rid of more waste. You’re getting rid of the same amount of waste, it’s just diluted in more water.

DR. JOEL TOPF: Yeah, so my, my tagline on Twitter says, uh, "thinking the kidney's product is urine is like thinking a factory's product is pollution." Urine is the byproduct. What the kidney produces is homeostasis.

JEN GUNTER: Um, so how much water should we drink?

DR. JOEL TOPF: We should drink enough water so that you're not thirsty. I tell my patients, you know, anytime that you're thirsty, go ahead and drink a glass of water and maybe have one glass of water on top of that, it's not going to harm you. But, uh, I don't, I don't advise my patients to, um, count their glasses of water unless, unless they have kidney stones in their past or if they have autosomal dominant polycystic kidney disease.

JEN GUNTER: If you have an intact thirst mechanism and you have access to water, are you going to get dehydrated?

DR. JOEL TOPF: No. Let's put it this way, people with increased sodium will drink from a toilet. The drive to drink in is so strong, right? You will not get dehydrated. If there's a glass within a mile of you, you'll get that water and you'll be fine.

JEN GUNTER: See? Now you can be liberated from any anxieties you’ve ever had about whether you’re drinking enough water. You're welcome! Then, Dr. Topf told me something really cool about how our bodies know when we’ve had enough water.

DR. JOEL TOPF: Yeah, so, uh, there are all the call Osmo receptors. They're located in a center part of the brain called the hypothalamus, and they're going to constantly measure the osmolality of the body. And. They're, they're actually very sophisticated. It knows when you're drinking and it'll start to suppress the hormone that drives thirst as soon as you start to drink.
Right. It doesn't even wait for that fluid to lower the osmolality in the body. It's absolutely aware of what happens when you drink and it says, Hey, we're going to slow this cycle down. We know that you're already compensating for what we're seeing, so it'll suppress those hormones that are driving that thirst once you start to drink,

JEN GUNTER: Yeah. I thought that was fascinating. You know, that it takes about 10 minutes for the water that you drink, you know, to get into your bloodstream and that your brain, you know, knows, you know, within a minute or so that you've consumed enough and it's already like making the calculations based on what it's sensing in your mouth and your esophagus. I mean, it's such a fascinating autopilot.

DR. JOEL TOPF: Right? It's just way more advanced than we had thought.

JEN GUNTER: The body is amazing, isn’t it?

Ok, I have a few more little things I want to clear up now that I have my own kidney consultant, so let’s play a game: Kidney Fact or Fiction.

[gameshow sound]

JEN GUNTER: Staying hydrated makes your skin glow. Fact or fiction?

DR. JOEL TOPF: Fiction, no evidence that it improves the glow of skin. That said, if you really get dehydrated, skin's not going to be in good shape.

JEN GUNTER: Drinking eight glasses of water makes your brain work better. Yes or no?

DR. JOEL TOPF: So there is some data that, uh, this was done in school children that increasing hydration right before some tests improved some aspects of cognition. There were two studies that I could find on this. Neither of them were very large. Neither of them are very convincing, but I also didn’t see the test that it’s absolutely fiction. I would guess fiction, but I would leave a possibility that there's some truth to that.

JEN GUNTER: Caffeine is a diarrhetic. Fact or Fiction

DR. JOEL TOPF: Fiction. This has been studied pretty rigorously. There is no evidence at all that caffeine dehydrates you. You can include that when you count your cups of water, if this is something that you'd like to do. And coffee is no different.

DR. JEN GUNTER: So there you go friends - if you’d rather have a cup of coffee than a glass of water, you do you.

Before I could let Dr. Topf go, I had just one more question: So I gotta ask - Do you check the color of your urine?

DR. JOEL TOPF: Absolutely. I'm like every other person. No, I'm always interested in it. because it gives me a, you know, it's a window into what's happening in my kidney. Right. And I'm all, I'm naturally intrigued by that, but I don't think it changes my behavior. If I'm thirsty, I drink.

DR. JEN GUNTER: You let your body, you let your body run the autopilot.


Here’s one of the big secrets of medicine: it's not as hard as you might think. And it certainly doesn’t all belong in ivory towers, or dressed up in lab coats.

DR. JEN GUNTER: I had an aha moment when I was 20 or 21 years old sitting in class in medical school and the professor started talking about hydronephrosis… the exact same diagnosis from when I was a kid… and he explained it in the same language as my pediatric urologist. I sat there thinking, wow. That knowledge has held up! What I heard when I was ten is not any different than what I’m hearing now ten years later in medical school. My knowledge has held up over all this time and how empowering was it for me to actually understand how my body worked when I was going through all those scary things.

A lot of medicine is very complex - and if you are going to be a doctor you need to know all the background and the nitty gritty details matters a lot.

But if you’re just worried about taking care of your own health, or your family’s, there’s a lot in your power to understand.

One of my favorite things about being a doctor is when I explain something to a patient about how their body works and they have that moment of realization. All the puzzle pieces fall into place and they say wow… I didn’t know how that worked, and now I do.

I hope you’ll stick around for the rest of this season of Body Stuff. We’ll be breaking down how your body works, while busting one medical myth at a time. Next week... we’re diving right in with your digestive system.

WILDER: Why does poop smell bad?
ROSIE: Because of the things inside.

DR. JEN GUNTER: Not many of us are comfortable talking about our poop… but I’m not many of us! We’re going to talk about why today we’re so freaked out by feces… and we’re going find out what our poop can tell us about our health.

Body Stuff is a member of the TED Audio Collective. It’s hosted by me, Dr. Jen Gunter, and brought to you by TED and Transmitter Media. This episode was produced by Lacy Roberts and edited by Sara Nics. The rest of the team includes Camille Petersen, Alice Wilder, Gretta Cohn, Banban Cheng, Michelle Quint, and Roxanne Hai Lash, Alex Overington is our sound designer and mix engineer. Paul Durbin and Neeraja Aravindan fact checked this episode.

Special thanks to my one kidney for keeping me going.

We’re back next week with more Body Stuff. Make sure you follow Body Stuff in your favorite podcast app so you get every episode delivered straight to your device. And leave us a review! We love hearing from our listeners.

See you next week!