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Myths And Tips On Keeping Your Cool This Summer


This is SCIENCE FRIDAY. I'm Ira Flatow. If you're out shooting hoops this summer or you're going for a jog, you know it won't be long before you're sopping wet and, you know, it's really sweaty out there. And where's all that sweat coming from? Your body's water supply, of course. You have to replenish those fluids if you sweat a lot. But it's not as simple as the old eight-glasses-a-day mantra. How much should you really drink? Too much water, you can die, as has happened to marathon runners who chugged too much water during the race.

But, of course, too little water and you can get heat stroke, and you can die that way instead. And what about plain old water? Is that good enough? Do you have to have these expensive drinks that are all out there in the market? So what are some of the secrets for staying hydrated? Do you use your thirst as a guide? Is it too late once you feel thirsty? Are the sports drinks any better, and what are electrolytes anyhow? Well, joining me here to demystify the art of hydration is my guest, Douglas Casa.

He is chief operating officer at the Korey Stringer Institute at the University of Connecticut in Storrs, Connecticut. He joins us by phone. Welcome to SCIENCE FRIDAY, Dr. Casa.

DR. DOUGLAS CASA: Oh, thank you very much for having me.

FLATOW: When you exercise in this summer heat, what's the best way to hydrate? I hate that word. We use to all say drink, you know, to have something. What's the best way? What are - give us some of the rules of thumb.

CASA: Well, first of all, I mean, what you just mentioned earlier, I mean, thirst is an outstanding way to get a general sense of what your fluid needs are. And for nearly all athletes, especially recreational athletes, if they heed their thirst, they're basically going to keep themselves in a safety zone. So as long as they have an access and constant supply of fluid available for when they become thirsty. Thirst has obviously done a great job from an evolutionary perspective for keeping the human race, you know, thriving for a very long period of time.

So it gives us a good overall indicator of what our fluid needs are. And if we heed that, we're probably going to do a pretty good job. But if you're talking about a little higher-level athlete where, you know, performance is a key factor and we get into some more safety issues, we try to recommend people obviously always still use their thirst, but get into what we call an individualized hydration plan where they start to learn what their actual individual fluid needs are, like their sweat rate, actually make sure they have the proper amount of fluids with them so if they're out in a long activity or they're prepared, you know, for the second half of a soccer game or the fourth quarter of a football game, that they're well-prepared to make sure that that dehydration does not cause either a health issue or performance decrements.

FLATOW: How does a high schooler figure all that out, though?

CASA: That's a great question. I mean, there are some basic cues that people can start to use, I mean, things like urine color. When your urine is dark like apple juice, that's a very good indicator that you're dehydrated. When it's light like lemonade, you have a good idea that you're probably hydrated. So that's something they can make sure before practice begins or in the hours leading up to a practice or a game. It gives some people a general indicator. We use body weight changes before and after activity.

We educate runners and triathletes all the time when they go out to workout sessions to weigh themselves before and after. In fact, on your show, I mean, on NPR a few years ago, I demonstrated how you can easily figure out your individual sweat rate. I mean, basically, you weigh yourself before, you weigh yourself after, and you can figure out if you're rehydrating the proper amount of fluid during that activity because, as you mentioned earlier, you absolutely want to make sure that you're not overhydrating because something called exertional hyponatremia could certainly cause people to have problems, and we see that more in recreational athletes in long-term activities like in a marathon.

But, without question, you don't want to get dehydrated either because we found in recent research that for every additional 1 percent body mass loss, your temperature is almost a half a degree higher Fahrenheit. So that means a football player leaving a practice field could be like two degrees Fahrenheit higher just because they did not hydrate properly.

FLATOW: 1-800-989-8255 is our number. Talking with Douglas Casa. Is plain water good enough?

CASA: That's a good question. In most activities for a lot of people, lower-intensity stuff, water is obviously a great rehydrator. But when things get - if it's intense exercise in the heat and it's something that's longer than an hour, getting the other things in that fluid - the carbohydrates, a little extra energy, getting the electrolytes and the sodium, which helps with the rehydration process and, importantly, the flavoring as well. Generally, people ingest more of a flavor they like.

Those things could certainly be helpful. So there's a reason why sports drinks, you know, have been very successful for a lot of people for a number of years. And if someone is doing intense exercise in the heat, there are certainly circumstances where I think it would be better than water.

FLATOW: Should you be taking salt tablets if you're doing that?

CASA: That's a good question. If it's a serious athlete who's doing prolonged exercise in the heat, we do. There are a lot of people who supplement with sodium, but they got to make sure they chase it with the proper amount of water so that it's being diluted properly. That's where we got into a lot of the problems in the late '60s and the late '70s when football players were just popping salt tablets but not the proper amount of fluids. So elite triathletes and marathoners, you know, they know that they need to supplement with their sodium because there's not enough sodium in a sports drink to, you know, to compensate for the losses that you have during intense exercise in the heat. So yes, there are circumstances where you would have to supplement the sodium even above and beyond what's in a sports drink.

FLATOW: Mm-hmm. Talking with Douglas Casa. And the reason I'm saying that is because I was watching on YouTube a talk you gave about high school athletes and how the coaches really have no idea how to treat them in the heat, and how to condition them in advance in the heat. And they send them out in blazing heat without any conditioning, and some of them drop dead.

CASA: Yeah. That's - one of our main missions at the Korey Stringer Institute is to try to prevent sudden death in sport. The problem of athletes dying has gotten much worse in the last few years. In fact, the last five years has been the most number of heat stroke deaths at the youth level in the last 35 years, and a lot of it does have to deal with the lack of education with high school football coaches and the lack of having athletic trainers, the proper medical staff there available for these athletes.

We're working state by state right now to try to get them to change what's called the heat acclimatization policies, which is the phasing-in of activity during the football practices at the high school level in August. The NCAA for college did it in 2003 to great success. It's probably saved 20 to 25 lives, their policy change back in 2003. The NFL did it last summer with their new collective bargaining agreement.

But at the high school level, you have to go state by state. So in the last 13 months, we've helped seven different states meet the minimum standards for heat acclimatization, and we're helping about 11 others right now. But we're trying to get all 50 states on board for heat acclimatization policies, which could go a long way to protect these high school athletes.

FLATOW: Yeah, because you're saying that, you know, they go out in the middle of - the first day there, they're doing three-a-days, as anybody in sports knows, something like three-hour workouts a day in the middle of the heat. And they - it takes what? How many days to acclimate to the heat? And they're doing it on day one?

CASA: Five to seven days, you're probably getting about 90 percent of the benefit. So yeah, that's why we're - these new policies with heat acclimatization is really trying to change that first week of practice to make sure we protect the athletes. They're most likely, by far, to die in the first three days of practice. So we have to make sure we do anything possible to keep them cool and hydrated during those first three days and protect them.

FLATOW: And you say the worst person who can treat them is the high school coach.

CASA: Yeah. I mean, if you're a parent, you should be kind of scared if the high school football coach is the one who's recognizing what the condition is and treating the heat stroke. The proper medical professional to deal with emergencies in sport are athletic trainers, but only about half the high schools in America have an athletic trainer on site. So we're also working hard to make sure that these high schools have the proper medical staff there on site to take care of these athletes.

FLATOW: All right, let's go to the phones, lots of people with questions. Let's go to Justin in Kalamazoo, Michigan. Hi, Justin.

JUSTIN: Hi. Thanks for taking my call.

FLATOW: You're welcome.

JUSTIN: I was just curious. With regard to your comment about weighing yourself previous to your runs and after you runs to gauge your dehydration, don't you burn calories during the run? And how long or how much should that take effect in how much water you drink during your run? I'll take my comments off the air. Thanks.

FLATOW: You're welcome.

CASA: That's a great question. It is true that about, you know, eight to 10 percent of that weight loss during the activity might be due to the caloric expenditures. So that - the weight change during activity is obviously not a perfect science, but it gives you a very good estimate of what the weight changes are during activity because, obviously, the great percentage of those are due to sweat losses. And during intense exercise in the heat, it's even a greater percentage due the fluid losses. So that is a very good question, and it's something you would factor in. But during an hour of activity, which is what, when we used people to help them calculate their individual fluid losses, it's not that much of an important factor.

FLATOW: Let's talk about drinking coffee or caffeine. Does caffeine dehydrate you?

CASA: That's a great question. We have found that in four different studies we've done with caffeine during exercise, that caffeine in no way inhibited the rehydration process during exercise. So now, at rest, it might act as a mild diuretic. But remember, it's still - you're still hydrating if you're drinking a caffeinated beverage. You just might not retain quite as much as if you were just drinking straight water.

But during activity in the heat, we found that the body must, you know, have its own ways of knowing that it needs to retain fluids. And that mild diuretic influence you might get during rest does not show itself during exercise, during, you know, a typical dosage that you would with the caffeine with, you know, uses that we see in our society. So we have not found that to be true. So that we have made - believe that's an old wives' tale.

FLATOW: Mm-hmm. What about - speaking of old wives' tales, what about coconut water? Is there anything about, you know, drinking that?

CASA: Well, that's a newer wives' tale, yeah, coconut water.


CASA: Like I said, coconut water is another way of hydrating yourself. You're getting fluid in, so that part is positive. But we don't see that there's any added benefit, of anything magical about drinking coconut water, that's above and beyond what you might get with a sports drink, for instance.

FLATOW: Charlie in Boulder, hi. Welcome to SCIENCE FRIDAY, Charlie.

CHARLIE: Hi. Thank you. Great to hear you. I love your program.

FLATOW: Thank you.

CHARLIE: I'm a river guide in the Grand Canyon. Just came off a trip where it was 120 degrees and we still do hiking. We have three different powders that we offer to people for hydration: a Gatorade, a lemonade and an electrolyte replacement powder. And I'm wondering if the sugar - if there's any downside to the sugar-based powders - Gatorade and lemonade - and it's more preferable or more efficient for just the electrolyte replacement powder?

CASA: That's a great question. It would really be circumstantial. If a person is getting in proper amount of calories while they're hiking and they have proper foods available to them, then it wouldn't really matter that they'd need it. They wouldn't really necessarily need the calories from a sports drink. And as long as that sodium can be diluted in the beverage you're using where the taste is not compromised, where they still can drink a proper amount of fluid, then I think you're fine. If they're not, they don't have good access to food or calories and they're not feeling like they really want to eat much during it, then the calories you get in a sports drink might be beneficial for that person during that activity.

FLATOW: And what exactly are electrolytes?

CASA: Electrolytes - you have a lot of different electrolytes. But one of the common ones that you hear about all the time in the news are things like potassium or sodium. And sodium is one of the most common ones because it has so many different influences in maintaining hydration in your body. And we lose sodium in our sweat when we exercise in the heat, and we tend to lose even more when we first start exercising in the heat, before we get acclimatized and - but that sodium is also really important for, like when you ingest fluid with sodium, you tend to retain more. It tends to keep the thirst mechanism on longer, which is helpful for gauging the proper amount of hydration. In small quantities, it helps enhance the taste of the thing that you're ingesting. So there is some benefit to having some sodium - small amounts of sodium in a beverage like you would see in a typical sports drink.

FLATOW: This is SCIENCE FRIDAY from NPR. I'm Ira Flatow, talking with Doug Casa. He is from University of Connecticut in Storrs, talking about sports. A little bit more talking about high schoolers and sports, because you were talking a while back that in the last five years, we've seen more deaths than in the past 35 years, on the playing field. And August now becomes the month, right, where kids are going to go out and try out and get conditioned for the football team.

CASA: Yeah, no question. I mean, August certainly is our - at the high school level, is our riskiest month. But ironically, in the last few years, we've really started to see more problems in July, because the high - at the high school football level, we're starting to see the conditioning sessions. They're trying to mimic big-time collegiate programs now. And the problem with that is that the big-time collegiate programs have athletic trainers and team physicians and proper medical staff and properly trained strength and conditioning coaches. But at the high school level, we often have like captain's practices or maybe a lesser trained assistant coach. And we're starting to see a lot of problems at the high school level in July during the conditioning sessions where they just don't have the infrastructure to take care of the kids

FLATOW: All right. Thank you very much. This is very informative about the heat and informing parents what to watch out for their high school kids. Thank you very much, Doug.

CASA: Oh, thank you very much for having me. Have a great weekend.

FLATOW: You too. Douglas Casa, chief operating officer at the Korey Stringer Institute, University of Connecticut in Storrs. He was joining us from U.C. Storrs. Transcript provided by NPR, Copyright NPR.