TED Talks Daily - Sunday Pick: How much water do you actually need a day?

Episode Date: July 21, 2024

Glowing skin, increased energy, higher mental function and weight loss: These are just a few of the benefits we have been promised for the low cost of 8 glasses of water a day. But can this magical elixir really do all that it claims? Dr. Jen Gunter takes us behind the fascinating (and scandalous) history of hydration pseudoscience, unpacks the investigative report that ROCKED the beverage industry, and sits down with a nephrologist who tells us what's fact and what's fiction about our kidneys. It will quench your thirst for the truth about hydration. You can read the text transcript for this episode at go.ted.com/BodyStuffTranscript1

TED Audio Collective. Hey TED Talks Daily listeners, I'm Elise Hu. Today we have a special treat, an episode of another podcast from the TED Audio Collective, handpicked by us for you. It's hot out there, which means we should all be reaching for water. But how much do we really need to drink? You're about to hear an episode of Body Stuff that goes beyond the eight glasses of water a day phrase

and explains the science behind healthy hydration. You won't want to miss it. And you can check out Body Stuff wherever you get your podcasts and learn more about the TED Audio Collective at audiocollective.ted.com. We'll get to the episode right after a quick break. Support for this show comes from Airbnb.

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Follow Disruptors on Apple Podcasts, Spotify, or your favorite podcast platform. I'm Dr. Jen Gunter. I love science, and I hate when people twist it. Your immune system needs a boost. Herbal supplements, milk, eight glasses of water. Seven days a week. And there's a lot of twisted medical misinformation out there. There are toxins literally purify your mind. That's 64 ounces straight. 64 ounces. 100 ounces.

Yeah, that's ridiculous. Water. Chugging a gallon of water means you'll eat fewer calories. Oh, it's so painful. We're exposed to medical myths, whether we're 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. You need eight glasses of water a 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.

It works like an exquisitely designed atomic balance machine, right? You need to keep everything in balance. But first, I want to tell you about something that happened to me when I was 10 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 become 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 snowstorm to me. But 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, meaning 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 she was very confused. I think the doctor could tell as well. And so he gestured to me and 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 worked 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 love 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 surgery to remove my left kidney.

I've 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 firsthand the problems that happen when people get misconceptions about their health. And a lot of these 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 that 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're making sense in a sort of science-ish way, like the eight glasses of water a day thing. Hey, 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 as 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 into 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 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 sadly 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 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. Sometimes water just isn't enough.

Dry house. Time to refuel. Unquenched thirst has become a chronic problem in America. If you are going to sell something, you've got to have a reason to sell it. You've got to create a market for it. Water just isn't enough. Quenched thirst. Things like pre-hydrate. I mean, what's that mean? Drink ahead of your thirst.

Train your gut to tolerate more fluid. Your brain doesn't know when you are thirsty. 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. 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 developed this drink for the Gators football team.

It was effectively water, sugar, 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 Quaker Oats, and they spotted a big market. And that's really where the science of dehydration started. Okay, 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. But this is healthy people. So this is a whole different phenomenon.

And so what they turned into an illness was exercise-induced dehydration. Exercise-induced dehydration. Exercise-induced dehydration. 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 all about the science, then people are more likely to believe it. 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. Some of the studies we were actually having a bit of a laugh about. So what you would do is you would starve people overnight. 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. And 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. 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. 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 dartboard at some point. 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. 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 they'd be like, yeah, it's just kids running around. They just need to pee all the time.

So kids running off constantly. Even the U.S. military was in on the quasi-science. In the early 80s, 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 bonk. 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. 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 US, quite a bit of sources, and they tried to have studies published 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, sugary water, guys. I mean, how big a deal is this? 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. And it was like a holy grail. You go to sports conferences, sports medicine or sports science conferences, it's displayed everywhere, you know, sponsored. And you then criticize the sports drink. 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 now it's the number one 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 a minimum of eight glasses of water a day. After the break, we're going to talk about why this myth just won't die.

We're back. Before the break, we learned the origin of the eight 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 typically rely on two things, whether the information makes common sense and whether it feels familiar. But 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. There's 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, but it is grounded in funding for World Kidney Day, which I believe comes from Danon, a manufacturer of bottled water. It's like the deep state of hydration. That's Dr. Joel Toff.

He's a kidney doctor, otherwise known as a nephrologist. I called up Dr. Toff 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. Toff is just the chemistry wizard for the job. I'm a lifelong nerd who's been fascinated by the chemistry of body fluids going on three decades. I love nerds. 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 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. Dr. Toff 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.

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 Wii for a Wii. The radio station invited 18 contestants down to their studio to see who could drink the most water without having to pee. 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. 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.

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 water will shift from your bloodstream into your brain, cause increased swelling of your brain that causes headaches, nausea, seizures, coma, and death. And she ended up dying on her own bathroom floor a couple of hours later. 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. 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 process of maintaining everything in that tight band is called homeostasis. We've evolved to maintain homeostasis through finely tuned mechanisms.

The 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. I think that's perfect, right? So you can think about body temperature as 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.

Body temperature is just one example of the autopilots that our body has to maintain homeostasis. And our kidneys, well, 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 for maintaining pH and they maintain our level of hydration. One of these autopilots is called osmolality. And 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. In this case, the soup is our blood. To be a little bit 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 overhydrating while exercising. Doctors first started seeing it in ultramarathon runners and Ironman triathletes in the 1980s, a period of time that nicely coincides with the messaging coming out of the Gatorade Sports Science Institute. And it's 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 body's amazing ability to defend homeostasis. I just went for a run this morning. I went for a three-mile run and I'm a bit thirsty and a bit hungry. So it has my one kidney, because I only have one, keeping me working right. 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 osmolality back down. And the way that it does that is two factors. One, increased thirst. And so increased thirst is a sensation that your body

gets that'll change your behavior. It'll 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 that it does that is it's going to change the type of urine that you make. You're always making urine. You're always getting rid of, you're constantly getting rid of waste products. But one of the variables is how much water is excreted along with those waste products. 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. Yeah. So my tagline on Twitter says,

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. So how much water should we drink? 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 I don't advise my patients to count their glasses of water unless they have kidney stones in their past or if they have autosomal dominant polycystic kidney disease. If you have an intact thirst mechanism and you have access to water,

are you going to get dehydrated? No. Let's put it this way. People with increased sodium will drink from a toilet. The drive to drinking is so strong. 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. 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. Toff told me something really cool about how our bodies know when we've drank enough water. Yeah. So there are what we call osmoreceptors. 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 actually, the body is 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. 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. 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, you know, what it's sensing in your mouth and your esophagus. I mean, it's such a fascinating autopilot. Right. And it's just way more advanced than we had thought. The body is amazing, isn't it? Airbnb. If you know me, you know I love staying in Airbnbs when I travel. They make my family feel

most at home when we're away from home. As we settled down at our Airbnb during a recent vacation to Palm Springs, I pictured my own home sitting empty. Wouldn't it be smart and better put to use welcoming a family like mine by hosting it on Airbnb? It feels like the practical thing to do, and with the extra income, I could save up for renovations to make the space even more inviting for ourselves and for future guests. Your home might be worth more than you think. Find out how much at Airbnb.ca slash host. Okay, 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 little game.

Kidney fact or fiction? Staying hydrated makes your skin glow. Fact or fiction? 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. Drinking eight glasses of water makes your brain work better. Yes or no? So there is some data that 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 find the big test that said, this is absolutely fiction. I would guess fiction, but I would leave a possibility

that there's some truth to that. Caffeine as a diuretic, fact or fiction? Fiction. This has been studied pretty rigorously. There is no evidence at all that caffeine dehydrates you. You can include that cup of water when you count your cups of water, if this is something that you'd like to do. And coffee is no different. 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. Toff go, I had just one more question. So I got to ask, do you check the color of your urine? Oh, absolutely. I'm like every other person. No, I'm always interested in it. 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 naturally intrigued by that,

but I don't think it changes my behavior. If I'm thirsty, I drink. You let your body run the autopilot. Yeah. 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. I had an aha moment when I was 20 or 21 years old sitting in medical school, and the professor started talking about hydronephrosis, the exact same diagnosis that I had when I was a kid. And he explained it using the same language as my pediatric urologist. I sat there thinking,

wow, that knowledge has held up. What I heard when I was 10 is not any different than what I'm hearing now, 10 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're going to be a doctor, you need to know all the background and the nitty gritty details matter 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 the 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. Why does poop smell bad? Because of its things inside. 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 to 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 Lacey Roberts and edited by Sarah Nix. The rest of the team includes Camille Peterson, Alice Wilder, Greta Cohn, Michelle Quint, Banban Chang, and Roxanne Heilash. Alex Overington is our sound designer and mix engineer. Paul Durbin and Nirja Aravindan fact-checked this episode. Special thanks to my one kidney for keeping me going. We're back next week with more Body Stuff.

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