The science of optimal hydration ft. Colleen Munoz PhD

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What you’ll learn

  • What hydration and dehydration actually mean
  • How dehydration can affect your cognition, health, and muscle growth
  • Why your thirst may not be a good indicator of your hydration status
  • The truth about structured, gel and alkaline water

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Read the transcript

Daniel

My guest today is Colleen Muñoz. Colleen is Assistant Professor of Health Sciences at the University of Hartford, where she lectures on the principles of exercise science, cardiovascular disease, and human pathology. She’s also an active researcher on nutrition, exercise and stress physiology, with a particular focus on the genetic and molecular biology of dehydration and cellular stress, water intake and its effect on mood state.

In 2017, Colleen became the first female Young Researcher of the Year Award winner at the Hydration for Health Annual Scientific Conference in Evian, in recognition of her research on the effect of combined exercise, dehydration and environmental stress on markers of lipid peroxidation and DNA damage. Colleen, thank you so much for joining us.

Colleen

Thank you so much for having me on, and thank you for the lovely introduction.

Daniel

My pleasure! We often talk about the hydration or staying hydrated. What does it actually mean to be hydrated or dehydrated or even over hydrated? Are there any strict terms that we can apply to these?

Colleen

Traditionally speaking, the term dehydration is very clinical. Normally only relates to the elevated concentration of the blood, so that’s definitely something that’s commonly seen in a hospital setting, where you would probably see more extreme scenarios of fluid loss or lack of fluid intake.

So I think a lot of times people will start really using phrases like over- or under-hydration when we’re looking at daily intake and losses. So if somebody is under-hydrated, that suggests that maybe they’re not intaking enough fluid on a daily basis. And sometimes, you’ll see in the literature, people will call this group “low drinkers”.

And one more thing about those terms with dehydration, rehydration. I know Erica Perrier published a paper that kind of hinted at some of the terminology there – that that’s really more of a term for the process. So if you’re dehydrating, you’re losing body water, for example. If you’re rehydrating, you’re consuming water to gain body water back. Whereas sometimes people will use terms like euhydration, or hypohydration, or hyperhydration. Those terms are more generally used to describe a state, so a snapshot at a point in time, as opposed to the process of losing or gaining body water.

Daniel

Okay. So can you maybe, for those who are hearing about this for the first time, explain briefly what the differences between euhydration, hyperhydration and hypohydration are? And you also mentioned about compartments, right? I think most people are aware that their body is holding a certain amount of water, and that maybe with age this total body water decreases, but obviously water’s moving around the body as well. So we think about hydration, do we need to think about the different compartments in the body where water is being held, and how those changes happen? Can you explain some of those mechanisms for us?

Colleen

To start with the terminology – the term “euhydration” means that somebody is in an optimal body water balance. The term “hypohydration” suggests that they’re in a state of low body water, and “hyperhydration” is in their state of elevated body water.

Colleen Muñoz, PhD

So when it comes to the compartments, those terms are actually kind of related to even the conversation of body water compartments. So most of the time we break that down into the extracellular and the intracellular compartments. And when we say extracellular, we’re talking about the blood, primarily. And we’ll also include the interstitial space, which is describing the space in between cells. And therefore, when we talk about the intracellular compartment, we’re talking about inside of the cells. Most of the work has really been looking at the extracellular and specifically the blood compartments.

Daniel

So why is it a problem, for example, if we are hypohydrated or hyperhydrated? What are the consequences for the body in terms of health and also performance from each side, would you say?

Colleen

Well I think the much more established scenario has been with performance, and when we think about people who are exercising and especially exercising in the heat. It’s pretty clear now that there are some negative ramifications of being in a hypohydrated state, whether you start that way or you wind up that way during the event. And most of that comes down to a term called cardiac drift. So that refers to your heart rate and how your heart rate will continue to elevate, even if you exercise at the same intensity, as you are losing body water. So you’re sweating, for example. And it’s very clear that if you have elevated heart rate for a given intensity, that that doesn’t allow you to perform at your best.

Now this has been challenged by some researchers I know, particularly Timothy Noakes and some of his colleagues. I think one thing to consider is that some of the work that they did was definitely in a temperate environment, so it wasn’t a particularly hot environment where you would see some of those negative benefits. And the other thing is a lot of that work occurred in people who are very experienced athletes. We know now that, I mean, if you’ve ever been to a race any time recently, whether that’s a triathlon or a marathon or whatever, that’s not necessarily the majority of the population of the event.

A lot of times, we’re looking at what some people would call recreational exercisers. So maybe they’re not quite accustomed to exercising in a state of negative body water. That’s something that has been thrown out there, perhaps people can adapt to it. And I think we also have to be really cautious that they might not quite be as knowledgeable in terms of the health issues that can come along with elevated heart rate and elevated core body temperature.

Daniel

And we mentioned about, let’s say, loss of body of water, but there’s also the hyperhydrated state, having too much water. So one thing we’ve learned from our own research and work in the urine field is that if you drink a lot of water in one go for example, your kidneys are very sensitive to that. They essentially dump that water to avoid an excessive rise in blood pressure. And that can sometimes make you feel or appear more hydrated than you actually are, for example. Like, your urine’s really clear but it’s the water that hasn’t been absorbed. So if people who healthy and generally active, are there any sort of health and performance consequences for too much water intake, perhaps also in terms of the ratio of water to electrolytes, for example?

Colleen

Oh yes, absolutely. And that’s something that we’re always very cognizant of when we make recommendations, or even in some of our published works, that we always have to keep that in mind. So the issue would be water intoxication (or “dilutional hyponatremia”), both of which are describing the intake of water that’s enough that it would actually dilute the concentration of the blood. 

So like you said, the concentration of electrolytes are very tightly controlled, and if they get unbalanced in an extreme sense, that’s life threatening. So there’s unfortunately some famous stories about people who have consumed too much water and who’ve died. You know, I know one was based out of Los Angeles when they were competing for a Nintendo Wii, when it first came out. It was called “Pee for a Wii”, if I remember correctly. And of course, this was developed by a radio station, not physiologists. And they thought that, “Oh, what’s the harm in just having people drink as much water as possible?” And a woman died. So it’s not easy to do, but it’s absolutely possible. Especially if you’re not consuming regular meals, where you would get some of those electrolytes and you try to balance out the water that you’re intaking.

Daniel

So obviously having too much water is diluting the blood, and it’s diluting the concentration of electrolytes in the blood. One phrase I often hear is, some people say you shouldn’t drink too much water because you’ll “flush out electrolytes”. Is that really the case, or it just more a question of dilution? Because you’re drinking lots of water, more electrolytes are being excreted at the same time?

Colleen

Yeah, that’s definitely seemingly the issue. I’m not aware of any paper that’s directly looked at that question, but I have looked at some of the literature to see if there’s any evidence of that, and I’m unable to find it. So in one case, I know they looked at low drinkers and high drinkers, people who consistently drink low volumes of fluid versus high volumes of fluid. And with their 24 hour urine samples, there was a small difference, statistically significant, but a small difference in their urinary sodium output.

But again, that could very well be due to just sheer volume of water, and some of the sodium that got handled along the way. If I remember correctly, there also wasn’t a lot of information about their diets at the same time. I have a publication that actually showed that these “high drinkers” actually did tend to consume more of some nutrients. So they consumed more carbohydrates, for example, and more protein than the low drinking groups, so that could also explain it. A lot of what we eat will wind up in the urine as well.

Daniel

Ok, so they might be getting, you know, obviously sodium and potassium from the carb and the meat intake as well, so that could potentially be a compensating factor as well.

Colleen

Yeah, we could suspect that that’s the case. And I think the other thing that’s kind of interesting, I know Jody Stucky has a paper that looked at people who started drinking more fluid over the course of a fairly short period of time, maybe a week or something like that. But not only did they have diluted plasma, but they also had elevated aldosterone, which suggested that their body was actually trying to hold onto more sodium at that point. Aldosterone is a hormone that is primarily responsible for sodium retention at the kidneys.

So again, I think that’s another piece of evidence to suggest that you’re not necessarily flushing out electrolytes, you’re just diluting. Your body’s trying to balance once again.

Daniel

Interesting. Sweat measurements have taken a lot of interest. I know that in athletic practice, people often do test the urine before training, and then they do body weight measurements before and afterwards. With sweat, one question I have is obviously, it seems you do get some good actionable data, but are you only really measuring loss? You get data when you’re sweating, right? Can you actually get a sense of your starting point? Or is it more like a during and after situation?

Colleen

Measuring your sweat won’t really tell you the extent of your fluid imbalance, if you’re not addressing how you started the exercise, right? So if you started the exercise about hypohydrated, that’s obviously additive to the water that you’re losing during exercise.

Colleen Muñoz, PhD

Daniel

Right, so it’s like, I train, I sweat, that produces data on my electrolyte loss and concentration. But what I’m just curious to understand is, would that data enable me to understand my starting point? Or would I have to have a prior measurement that I would combine with the sweat data to understand the beginning and then the change at the end?

Colleen

Right, exactly. So all you’re looking at with the sweat is what happened during that exercise bout, right? So you don’t know how you started and really how those things add to really describe your fluid balance. So just because you lost, let’s say, a liter of water and looking at some of the electrolyte losses during your exercise bout doesn’t necessarily suggest that you are 1% dehydrated if you’re a 100 kilogram individual, or whatever that … So it wouldn’t tell you the whole picture. And there’s several studies now that showed that a lot of people actually start some of their exercise events in a hypohydrated state. So they’re not addressing the whole situation.

Daniel

Super interesting. And obviously, we also acknowledged urine has its drawbacks too, right? So studies in sports training typically show the weakest data for urine is people doing tests immediately after training, because urine’s not going to reflect those changes that fast. Or if there’s too much water being consumed, the water or the urine would indicate that they’re more hydrated than they actually are. So definitely pros and cons on both sides.

Colleen

Yeah, and I think that kind of gets to the idea of serial measurements, that if you take a bunch of different measurements multiple times throughout the day, then clearly you have a little bit of a better picture, right? It comes back to the context. So looking at all of that data together, you might actually be able to put together the story of how well did I do today in terms of my hydration status and my fluid intake.

Daniel

Yeah, I guess that leads to the topic of biomarkers, right? So there’s data which is gold standard, and then there’s data which is actionable. And the gold standard may not necessarily be the most accessible in terms of price and convenience, right? So if you were to … We know that we can use urine color, also in our case urine specific gravity, maybe other biomarkers as a measure of hydration status. But if you were to have any biomarker available 24/7 to understand your hydration the best, as accurately as possible, what would it be? Would it be plasma osmolality continuously or something else?

Colleen

You know what, just based on what we’ve seen with those low versus high drinkers, the plasma osmolality is not a good indicator for that, for the daily water balance question. The urine seems to be pretty valuable. Again, not that … Honestly, we don’t have a gold standard yet. We don’t have the perfect indicator, but we do have a collection of indicators that have a lot of value. And again, especially if we have the context in mind as well. So the urine’s great. There are definitely things in the blood that can be very valuable as well, even if it’s not plasma osmolality.

So people have been very in tune with a hormone called copeptin. And so, I guess, long story short, copeptin’s not necessarily new in some ways, because when it’s made in the brain, the other side of the protein is actually called AVP or arginine vasopressin – people used to call this the antidiuretic hormone. So both the antidiuretic hormone and copeptin are made in equimolar concentration, so they’re released in the same number, I guess, throughout. 

So antidiuretic hormone used to be really widely measured, but we now know that it’s really tough to measure. It’s not easy to measure, it’s in really small concentrations. I mean, some people have even said that they’re not totally confident of some of the data that had been published many decades ago, especially not knowing how finicky this hormone was to measure. So then, it was discovered that copeptin really still represents how much AVP was released or antidiuretic hormone was released, so let’s start measuring copeptin. It’s way more stable. It’s generally easier to measure, and we can rely on it a little bit more.

So copeptin has a lot of value. It will indicate whether or not you are in fluid balance. The only issue with copeptin is if there are other stressors, because it’s actually a stress hormone in many ways, because it’s released with other stressors, like exercise for example. So that starts to lose some value if we start having people work out and we want to measure their body water balance.

There are definitely some other hormones that people are interested in as well – angiotensin II, aldosterone, renin, some new ones like apelin.

I think honestly from my standpoint, our best variables right now to look at somebody’s body water balance will be the urine, and it will be plasma copeptin, especially if we’re looking at hydration status across days.

Colleen Muñoz, PhD

Daniel

Is thirst a lagging indicator of hydration status, or is it generally enough to follow it? Should people treat their thirst as a reliable indicator of hydration status?

Colleen

The literature consistently shows that thirst lags. Normally, what you would see is that by the time somebody’s thirsty, they’ve already lost 2% of their body weight attributable to water.

Colleen Muñoz, PhD

Daniel

Wow.

Colleen

Yeah. Which, I mean, seems significant, and even on a day-to-day basis, it seems that that could still be enough of enough water loss or enough of insufficient fluid intake to have some impact. Again, getting back to what we see with some of the cognitive data with low fluid intakers, also with mood and things of that sort. So it does seem to lag. Now at the same time, it’s kind of interesting that the clinical world hasn’t really seemed to adopt that information. 

Definitely, a lot of people are still under the impression that thirst should be the end all be all indicator for when we need to start drinking fluid. But another piece of evidence to suggest that shouldn’t really be the recommendation … we have many studies now that show people who drink as much as three and a half liters a day, versus people who drink as little as one and a half liters per day will often have the same thirst perception on a daily basis. Or sometimes it even goes the other way, that the high drinkers actually feel a little bit thirstier than these “low drinkers”. So I think that that’s another piece of evidence to suggest that thirst isn’t valid in terms of monitoring fluid balance entirely, I should say.

Daniel

So is it possible to be, at least perceive yourself to be thirsty, but actually be fully hydrated or euhydrated, I should say?

Colleen

Well no, that’s another good question, because we get back to where is that water, in what compartment, and so some people would argue “yes”. But at the same time, that if we get back to their blood concentrations, their blood concentration tends to be the same too. Again, these people who drink a lot versus these people who don’t drink very much at all. So where’s it going? And the only thing I can think of is, obviously, some of it and more of it’s going to be expelled through the urine. But I think there’s a good chance that there’s probably a little bit more water in the cells of those high drinkers than the low drinkers. Now that’s me, again, speculating. We don’t have great evidence of that, and especially not in a human model.

Daniel

Yes. So clearly there are direct physiological effects of, for example, dehydration on the body. How much do you think perception and mood plays a part? I’ve looked at some sites before about the effect of dehydration on cognition, for example. And one of the potential issues here is that the feeling of actually being thirsty itself can be a mental distraction, right? And then separating what is the perception of the state from the actual physical state is an issue.

So in my case, for example, let’s say I’m having a … it’s a very rough parallel, but I’ve had a long day, I’m stressed, I’m tired, I’m a bit hungry. And maybe I might give myself a break and not go to the gym, but I’ve noticed that some of my best workouts have been when I’ve felt relatively tired and lethargic, but when I’ve gone and it’s been a fantastic session. But it was that perception initially which was kind of holding me back. But physically, I’m able to perform as good, if not better than I normally would.

So let’s bring that back to hydration side. When you’re trying to assess the effect of dehydration on performance, how important do you think are the subjective factors, not just objectively what’s happening to the body?

Colleen

Oh, it’s huge. Yeah, and I think a lot of people have experienced similar things to what you just described. So thirst is definitely one thing. You know what? I got to say, I’m not super familiar with any literature that looks at just the perception of thirst on performance, but definitely there is the perception of intensity. So people who would look at the rating of perceived exertion (or “RPE”), which is directly tied to your heart rate. So once again, if you feel like you’re working hard, it probably actually means that you’re physiologically strained, and therefore not performing very well.

But there’s actually some brilliant work out of New Zealand, Toby Mundel’s lab actually did this a number of years ago, where they used capsaicin to mimic a skin temperature that felt hot, but their skin was not actually elevated, their skin temperature wasn’t elevated. And then they used menthol to mimic the feeling of cool skin, and they found that in fact, just the feeling of being hot, even if your skin wasn’t actually hot, did negatively impact exercise performance. So yeah, I think absolutely, perception is something that we can’t ignore.

Colleen Muñoz, PhD

Daniel

That’s super interesting. I think I’ve seen a Danone sponsored paper on this, but people were looking at – is your hydration status affected by the form in which you drink water? So if it’s pure water, is it as part of an electrolyte drink? Is it part of a yogurt drink, or something? Do you have a view on that? Is it possible that people who are drinking more in a less easily retainable form are actually experiencing more loss, compared to those who might drink less, but actually have it in a form where it’s less easily lost from the body? All else being equal, of course.

Colleen

Assuming I understand correctly, I think one of the things that we need to think about too is, what else is coming in with that water? A lot of times, we’ll refer to this as total solute. So it’s the particles that are coming in with it that are osmotically active, so that bring water with them, or attract water so that stays in the body, versus getting expelled in the urine.

So if you do have people who are consuming a lot of fluids in their foods, you could argue that that might be a situation that allows them to retain that water better. Something that I, to my knowledge, nobody’s specifically studied, but in theory and in piecing things together that that would make sense.

Daniel

Okay, okay. So would you recommend people to avoid just drinking pure water, or would it be a mix of that and maybe electrolyte drinks? Or say, if you’re drinking water with your food, it’s probably not an issue, because the food itself is containing some of those solutes which will help retain the water?

Colleen

Yeah, more of the latter, so as long as they’re consuming it with food. Or honestly, it doesn’t even have to be directly with food probably, but as long as they’re intaking regular meals, then they should have the solute in their body to keep the water in their body, versus going through the urine instead.

Daniel

Okay. That’s super clear. Thank you. One topic that made me want to reach out to you is something I’d seen trending, a concept of structured water or gel water. So, essentially, people are saying that it’s not enough for you just to drink standard water. It’s not, almost, chemically in the same structure as water as held in the body, and, therefore, we need to take a different approach to hydration. This is something I’m relatively new to, but is this a topic you’re familiar with? Do you have a sense of why people are talking about this? Is there any kind of proper research behind it?

Colleen

Yeah. There’s always something new that people are bring out in the hydration world. I wouldn’t say that this is something … I’m not a physicist. I’m not normally in that particular world. From what I have read about it, it seems like one of the benefits that is purported is that it changed the pH of the water and, therefore, apparently makes it more accessible to certain compartments. I think the pH alteration isn’t one that most people in the hydration world have bought.

Anybody who studies physiology knows that pH is incredibly tightly regulated. So, if you do intake something with a lot of alkalinity, it’s very likely that your body’s going to adjust for that pretty rapidly. I think we also have to keep in mind how much water is really in the body. 

Even if you take in a liter of something that has a higher pH, that’s really a drop in the bucket. Is it really making a difference from a whole body standpoint that could equate to some health outcome? I think it’s a tough sell.

Colleen Muñoz, PhD

Daniel

Does the time of day affect hydration levels? Do we have a natural diurnal variation in our hydration status? Is it really about our diet, our activity, our environment, that really is the key issue here?

Colleen

Yeah, there is a diurnal variation, and I always find that so fascinating. Evolution – brilliant! So what you would actually see if you studied a lot of the hormones that are responsible for maintaining body water is that the ones that are supposed to retain body water will actually be in elevated concentrations in the blood at nighttime. Assumingly, because you won’t be drinking any fluid while you’re sleeping. Your body tends to realize that, and so it’s a way to make sure that you hold onto some water knowing that you’re not going to have access to it for a while.

And then in the morning, those hormones start to go away a little bit, and you go back to your normal routine, that if you’re consuming water then you’re going to expel something into the urine. So yeah, there is diurnal variation, and that also means that when we’re collecting hydration biomarkers, whether that’s in the urine or the blood, we always have to keep that in mind when we’re interpreting that.

So if anybody’s ever paid attention to the first time they urinate in the morning, they probably noticed that it looks quite a bit darker than it does at other points throughout the day. And that’s really a reflection of those hormones, it’s because your body was retaining water, therefore it wasn’t willing to get rid of it in the urine.

Colleen Muñoz, PhD

There’s actually some interesting data to look at the afternoon as well. So the afternoon single sample … so if you where to do a spot sample of your urine, for example, the afternoon hours – if I remember correctly, somewhere in the like two to 4:00 PM range – seem to most reflect the 24 hour sample. So if you were to collect all of your urine for 24 hours to really get a good look at how well you’re hydrating on a daily basis, that window in the afternoon seems to best reflect that, if you don’t want to collect all of your urine for 24 hours.

Daniel

Okay. We also know that body water levels decline with age. So can we top up our levels by drinking more water, or is there a way to actually respond to that, or is it something that is pretty much unavoidable despite our water intake?

Colleen

So nothing that anybody’s experimentally tested, but in theory, the issue there is actually sarcopenia. Sarcopenia is the natural loss of skeletal muscle as we age, so it’s a naturally occurring aging process. So if you can delay sarcopenia, then in theory, you can actually maintain more body water as you age. And of course, there are ways to at least delay the progression or delay the severity of magnitude, so regular exercise is fantastic, of course. There are some people that are actually exploring – and I am one of them, I’m very interested in this – the relationship between water and taking skeletal muscle health.

There’s some great work by Florian Lang and his colleagues, Doctor Housinger. So, they used cellular models. A lot of the cellular models were actually liver cells. They looked at cell swelling and cell shrinking. So, basically, did a cell have a lot of water in it, or did a cell have not very much water in it? It’s some fascinating data. They have many publications on this type of work.

Largely, what they see is that when there’s a lot of water in the cell, it is anabolic. That means that it’s in, really, a building phase. It’s storing nutrients. It’s making new proteins. When it’s smaller in size, because it’s lost a lot of water, it’s actually catabolic. So, it’s breaking down. You wind up with less protein synthesis. You wind up with, what some would consider, an unfavorable metabolic state.

Colleen Muñoz, PhD

Daniel

That’s absolutely fascinating. I’d love to look at that paper. Now I need to drink more water!

Colleen

They have a bunch of wonderful work. Yeah. This is where it all comes back to thinking about the muscle. I mean, obviously, I have a little bit of the interest in the athletic world, but even for the general population, if there’s more water going to the cells, if we’re hydrating very well, is this favorable from the muscle cell standpoint? I think it is. It seems, in theory, that that’s probably what we’re looking at there.

Daniel

Ok, obviously muscle contains water. Would that be one of the main causes of loss of body water due to loss of muscle mass? Is that the idea?

Colleen

Correct. Yes, that is the current thought. Another thing to consider is there’s definitely a decline in the thirst mechanism as we age, so that’s been well documented. So older adults don’t seem to be having as much of a drive to intake water as they age. And the other thing is, and whether these things are related or not is up for debate, but there seemingly are some hormonal changes as well that might be contributing to the decline in body water.

Daniel

That’s super interesting. Actually, one of the other guests who’s, I’m recording soon, Brianna Stubbs, she’s a former Olympic rower who used to be research scientist at HVMN, did a lot of work in ketone esters, and sort of very much on the biohacker-performance side. But she’s now at The Buck Institute for Healthy Aging. So it’s really interesting to see that trend from people like her and yourself going originally from the performance side and now looking more holistically.

I think this is a really healthy trend that biohacking’s being such a … and also research has been a great source of trying to get validated insights and pushing the envelope for people who are perhaps less casual, but now bring this to a wider area. People can say, “Well, look. Maybe in my 20s and 30s, I wasn’t all about having the extra 1-5% so I can be “killing it” in Silicon Valley, but actually I want to live long and as healthily as possible and have a good life.” So I think this is a really encouraging trend that can touch lots of people’s lives.

Colleen

Yeah, I think there’s a lot of people that are focusing on aging more, much more so than they ever used to, so that’s an exciting field as well.

Daniel

Colleen, thank you so much for joining us. It’s been a great conversation.

Colleen

Thank you!

You can follow Colleen on her Twitter and learn more about her here.

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