Your emotional support water bottle is probably too big

Tegan Taylor: Norman, are you a Stanley girly or Frank Green girly?

Norman Swan: I don't have a clue what you're talking about. 'Frank Green' doesn't sound great but, you know, 'Stanley' sounds fine, but I don't know what I'm committing to here.

Tegan Taylor: It's a water bottle thing. If you know, you know.

Norman Swan: So, no, neither, I don't have a water bottle.

Tegan Taylor: You don't have a water bottle?

Norman Swan: Even when I go to the gym, I don't have a water bottle.

Tegan Taylor: How do you signal to the world around you that you stay hydrated and are also on trend?

Norman Swan: I walk over impatiently to the water fountain and stand there while people fill those Stanley Green and…whatever the name is, Frank Green and Stanley water bottles, and I go…I just want a sip of water, thanks very much.

Tegan Taylor: So you just sip straight from the water fountain?

Norman Swan: Well, not my mouth totally over it but yeah, yeah.

Tegan Taylor: That's so old-school, I love that for you. Well, you've got to have seen these bottles around, right?

Norman Swan: I have. Now that you've mentioned it, I have. I just don't look at the brand.

Tegan Taylor: How much would you spend on a good-quality aesthetically-pleasing water bottle?

Norman Swan: $1.50, $2.00?

Tegan Taylor: Keep going, keep going.

Norman Swan: Oh really? How much are they?

Tegan Taylor: I want you to guess how much.

Norman Swan: Oh God…$15.95?

Tegan Taylor: More.

Norman Swan: More!

Tegan Taylor: So much more.

Norman Swan: You're kidding me!

Tegan Taylor: The brand-name ones are between like $60 to $90.

Norman Swan: What a rip off.

Tegan Taylor: Water rip off, indeed!

Norman Swan: This is now flooding back to my last trip to the gym. You see people with like one gallon in…

Tegan Taylor: You've got to go to the gym to be strong enough to lift the water bottle to your lips. It's kind of like a bicep curl action. Well, let's get into it because we're going to talk about it in depth today.

Norman Swan: Yes, in What's That Rash? where we answer your health questions.

Tegan Taylor: So today's question comes from Daniel who asks, 'Do I really need to drink two litres of water per day? I always thought so. But lately I've been reading that it's not necessary.' I think I know what Daniel's been reading.

Norman Swan: What's he been reading?

Tegan Taylor: Well, there's a study…well, it's sort of a review of the evidence that came out a few years ago now that looked at the origins of the water recommendations that get bandied about, and it's actually really murky. Not the water, the guidelines,

Norman Swan: They are, for all sorts of reasons. But why don't you take us through some of the evolution of water drinking before we get to this question that Daniel has asked, which is a very sensible one. You walk through an average office, walk through the ABC here, I don't know if you've got your expensive bottles, but there's plenty of people with bottles of water on their desk knocking it back.

Tegan Taylor: So I want to talk to you about two types of evolution, one human evolution, one of my favourite things to talk about, but also the evolution of the eight glasses a day thing, which I don't know where I thought it came from but I've managed to trace it back to 1945. And it was based on millilitres per energy expended across the day and then what that would translate in terms of water intake across the day. And basically for the average human it translated to about eight glasses of eight ounces each, which not only is sensible and basic maths, it's also very like meme-y, it's the sort of thing that people can kind of get around, it's a bit like the 10,000 steps thing. What the recommendations kind of miss though is the nuance around how much water you may be getting in your food or other fluids you might be drinking throughout the day, like it doesn't have to necessarily be eight glasses of water, in addition to everything else you put in your mouth.

Norman Swan: And here's the key, which is partly the answer to Daniel, it's about whether you force yourself to drink these eight classes a day or you take it in anyway.

Tegan Taylor: Yeah, and I'm curious to ask you a lot more about that, but we did talk before about human evolution, and I was really surprised to discover that humans are real outliers when it comes to the amount of water we need. And basically, humans are very much designed to out-run big animals that we've hunted for game, because we can outlast them in terms of how we regulate our body temperature. And so a human can run across…not me, but another human can run across the savanna for hours and eventually wear out an antelope or something like that, and part of the reason we can do that is because our body is really good at shedding heat. And we do that through not having body hair and by having lots and lots of sweat glands. And so we're able to evaporate a lot of water off our bodies really quickly and keep that body temperature cool on the inside. A fantastic adaptation to running around on the savanna, but not so good if you want to keep water inside your body, and we don't have huge amounts of water storage in our body like, say, a camel or something does. And so there's this sort of push and pull with water and humans where we're good at getting rid of it, but we also need to replenish it pretty regularly.

Norman Swan: Indeed, but we're better than you think and better than people think when they feel they've got to drink two litres a day because we are actually quite good at controlling our water supply. So if you look at the physiology of it…shall I get into the physiology…?

Tegan Taylor: Yes, I love this, yes, please.

Norman Swan: So we have something…it's very old fashioned to talk about, it's called thirst, and thirst evolved for a very good reason, to make us drink, you know, to tell you; you need to drink, chum. So thirst is a feeling that we get when…and this is incredibly complicated and I'm going to oversimplify, but essentially when your blood becomes more concentrated and there's more electrolytes per litre of your blood or 100 mls of your blood, that's detected in your brain. It's also detected peripherally as well in your arteries by the volume of your blood going down when you're a bit dehydrated. And so you get multiple messages going to your brain, a part of the brain called the hypothalamus, which is, if you like, a master control centre for hormones of different kinds. The hypothalamus sends a message to a gland just very near it called the pituitary gland, which sends out another hormone called the antidiuretic hormone, and this stops you peeing, so it shuts down your kidneys. And one of the reasons you don't get up a lot during the night to pee compared to how much you pee during the day is that at night your antidiuretic hormone goes up to stop you peeing.

Tegan Taylor: Thank you, sir. I'm talking to the hormone.

Norman Swan: And then the kidneys themselves can go into action through hormones called renin and angiotensin, and they can preserve sodium, or not as the case may be, and they can switch sodium for water in your kidneys. Because water is so important and these electrolytes like sodium and potassium are so important to our survival, there are multiple mechanisms going on to control it. But the key message for us, grossly, is this old-fashioned thing called thirst.

Tegan Taylor: Well, this is it. So I want to talk about why it's so important because it's sort of baked into your answer a little bit there, things about blood volume and the concentrations of various substances in the body. And, like we were saying before, you know, you sweat out a lot of water. What is water doing in the body when it's at the right concentrations?

Norman Swan: Well, it's the substrate for pretty much everything. Water is just part of what we need to stay alive. It's what carries hormones, it's what carries our blood. Essentially there's water in our blood, there's water in our tissues. It's a carrier of substances inside our cells and outside our cells, and our cells are largely made of water. So effectively it's the medium, it's like you need water to cook rice, you need water to make yourselves work.

Tegan Taylor: So if our thirst is so good at telling us how much water we need, then why is there such a culture around drinking recommended daily intakes of water? And some of the water bottles that we're looking at have motivational messages written on the side like 'keep chugging' and 'you're halfway there', like you've got to force yourself to drink these two litres a day, when you're saying to me that our thirst cues should be enough?

Norman Swan: Absolutely and I can only assume that it's commercial, to help sell more $60 bottles of water.

Tegan Taylor: That makes more sense.

Norman Swan: And of course, water itself, if you're drinking water that comes in plastic bottles, is very expensive.

Tegan Taylor: But there's been big parts of human history and there are parts of the world today where drinking straight water hasn't been the safest way to hydrate your body, and people have drank beer, or tea or coffee…

Norman Swan: That's right. So essentially they're still drinking water, they're just taking it in another form. And for a lot of human history, it was beer or weak wine that people drank because the fermentation process also helped to sterilise the water as well. So there were various beverages which got round the fact that water was often unsafe.

Tegan Taylor: I mean, you and me, we could talk about Jon Snow and the Broad Street Pump all day long, that famous place in London where the father of epidemiology discovered the fact that basically people were dying of cholera because of tainted water. But the guys who worked at the brewers factory, they didn't get it because they had their own deeper well and obviously also had access to a supply of beer.

Norman Swan: As a very famous microbiologist at the University of Melbourne, Professor Nancy Millis once said, this whole evolution of human history is about separating the mouth from the anus.

Tegan Taylor: Okay, cool, we'll leave that one there. But okay, what about water from things that aren't liquid, like fruit for example, lots and lots of water in it. How much are we getting from our food?

Norman Swan: That varies according to your diet. So in some parts of the world milk is a major part of the diet, and in some parts of the world people eat a lot of fruit, and that will give them a lot of water, but most foods have water in them and it's hard to generalise how much water you get from food but it is a significant percentage. So, food gives you water as well. This is why the two litres a day thing is so artificial because we do it without thinking. I mean, a survey around the world of how much people drink without being prompted to drink tells you that, without thinking about drinking, we will consume, either by drinking or eating, between two and three litres a day.

So one comparison I want to make to give you some reassurance about the fact that you don't necessarily have to think about drinking your two litres a day…there are exceptions to this, by the way, which I'll come to in a moment. But if you look at the elite athletes, what's good enough for them should be good enough for you and I. I know you're an elite athlete, with your climbing and all your pre workout drinks that you're taking (pointing into a previous episode and also one of our great videos on Instagram). So elite athletes are evaporating a lot of water in their exercise, particularly if they're exercising in the heat.

And it used to be, for example, with marathon runners and other endurance sports, they would say stop at every water table and drink water, you've got to keep yourself hydrated, don't wait on thirst, get ahead of your thirst and drink. And what they found was the incidence of a very dangerous condition or potentially dangerous condition called hyponatremia occurred, which is caused by water overload where the sodium levels in your blood go down. And your sodium levels are very closely monitored by your kidneys and your hypothalamus because there's a very narrow range where, for example, particularly your heart can operate and your nerves and so on, and hyponatremia, in its most extreme form, can kill you. So what they found was that these athletes were developing hyponatremia, signs of water overload, and their times went down.

And research has shown, for example, in some endurance athletes that in fact their performance is at its best when they're just a little bit dehydrated, maybe 2%, dehydrated, and there's conflicting evidence there, but the overall message is if you're a little bit dry when you're doing elite sport, you're actually a bit better off, not a lot dry, but a little dry. And what coaches teach their athletes is drink to thirst. When you're thirsty, drink, don't force yourself to drink. And in fact, that was the recommendation of a group of experts who got together a few years ago to make recommendations on this. So if athletes don't need to force themselves to drink, I don't think you or I do either.

Tegan Taylor: Okay, then the flipside of that, if you've got a giant water bottle that's encouraging you to drink or that's something that you like to do, are you putting yourself in danger by drinking too much water?

Norman Swan: I think if you are incredibly obsessed by it and you go overboard and you're chugging large numbers of these bottles, then yes, but that would be an unusual situation. So the answer is mostly you're not, but you'll be going to the bathroom a lot to pee, you know, what goes in must come out. And in fact, if you go to the gym, your gym performance may be reduced because you're carrying more water.

Tegan Taylor: So bottom line, trusting your thirst is probably okay.

Norman Swan: It is, with exception. I promised at the beginning I'd come back to exceptions, and there are two; one is elderly frail people sometimes just don't drink enough and don't remember to drink enough and need to be encouraged to drink enough. The other is kids with autism spectrum disorder, they're not good at getting the messages from inside their bodies about hunger and thirst. So sometimes kids who are on the severe end of the autism spectrum disorder need to be encouraged to drink. But those are the two main caveats.

Tegan Taylor: So, thank you, Daniel, for sending in your question. And if you want to send a question, you can hit us up, we are thatrash@abc.net.au. We get more than questions at that email address, and I wanted to…well, I want to start it as a new segment, I'm calling it the N-of-one show-and-tell corner.

Norman Swan: Yeah, we love to give you new words on What's That Rash?, we've given you 'pleuk', we've given you 'doolally' and many others. And now we're giving you 'N-of-one'. So you'd better explain what N-of-one is.

Tegan Taylor: So N-of-one in an experiment, the number of participants is the N, and so in these experiments there's the N-of-one which is where you basically do an experiment on yourself or on one person and then generalise this result across a population.

Norman Swan: You're the one.

Tegan Taylor: You're the one. Anyway, Norman, Leia has messaged in telling a story about how she owned shares in a radiology practice and her partner at the time was the CT operator. And they had to do a test, barium dye, so basically when they give someone something to take so that then they can then do a scan of that person and then that thing shows up more clearly on the scan. Am I explaining it right?

Norman Swan: That's right, you swallow barium because barium is dense to X rays and when you swallow it, it can show up your stomach your bowel.

Tegan Taylor: So in this case what they needed to be able to do was image the oesophagus, so the pipe that your food goes down, and they thought that if they mixed it with a pre workout gel, they thought it would coat the oesophagus, hold the dye for longer so that it would show up on the scan. So this person and their boss decided to do a baseline test with just the pre workout gel rather than adding the barium…

Norman Swan: But not on a patient.

Tegan Taylor: No, no, on themselves of course, this is our N-of-one showcase corner. The test subject drank half a packet of bubblegum flavoured pre workout gel, was put into the CT scanner and scanned. And it turned out that the pre workout gel that cost $1.95 was more reactive to the CT then the medically recommended $95 barium dye agent, and it lasted longer in the body.

Norman Swan: God. Now, that sounds marvellous on one side but scary on the other. Does she have an explanation for why?

Tegan Taylor: She says that she gathered that the high concentrations of trace metals contained in the gel was the culprit.

Norman Swan: If that's a recommendation against pre workouts, it definitely is one.

Tegan Taylor: Leia, thank you so much for sending that in. If you have an N-of-one study that you would like to publish in this peer reviewed podcast, please email us, we are thatrash@abc.net.au.

Norman Swan: And don't experiment dangerous stuff just for the sake of getting on the podcast.

Tegan Taylor: Yeah, we take no legal responsibility for anything that comes out of it. But if you do it, please still send us a hilariously worded email so that we can read it aloud and be funny by extension.

Norman Swan: And tell us which ICU you're in, we'll send you flowers. And we'll see you next week.

Tegan Taylor: See you then.