Hydration: For Health and Performance

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As the weather starts to heat up, questions keep popping up around hydration.  This is a great topic to address for our first Q&A of 2019.  However, rather than look at each individual question, I’m going to post an article which addresses all of it.  What is the best way to stay hydrated through the day?  Is 8 glasses of water enough?  How much should I drink when exercising?  Do I need extra salt or electrolytes? 


I think everyone is aware that hydration is important.  While people may argue many facets of nutrition, this isn’t really one of them.  Sure, the finer points are debated in academic circles.  But there are no pro- or anti- hydration camps out there.  You’ll find those experts who recommend avoiding meat, and those who are proponents of meat intake.  There are low carb and high carb people.  But I’m not aware of anyone pushing for more dehydration.  Despite consensus on the importance of the topic, many of us fail to adequately hydrate for our daily lives.  Let’s take a look at how we can all do better.

Rather than take a deep-dive into the science, I’m going to offer some simple advice based on questions that you have asked.  If you want me to delve into any specific topic in the future, drop us a line and let me know. (info@podiumsportsmed.com)

Start your day with a big glass of water!

It sounds so simple, and it is.  But few of us do it.  Assuming you slept 8 hours, it has been at least that long since your last fluid intake.  While I’m not of the opinion that you are waking up in a massive deficit, you have certainly experienced fluid loss during the night.  Take the opportunity to turn the tide, right out of bed.  I recommend 10-12oz of room temperature, good quality water.  (I use a reverse osmosis filter mounted under our kitchen counter.). To this, add some fresh lemon juice and either a pinch of sea salt or some apple cider vinegar.  There are purported health benefits to these things, though none is firmly rooted in science.  That said, it tastes great, is essentially calorie-free, and certainly won’t hurt you.  In fact, you may end up wanting two big glasses of this concoction.  Go for it!  It’s a simple thing, but you’ll notice the difference.

Doesn’t coffee dehydrate you?

Nope.  Recent studies have confirmed that caffeine does not have a significant diuretic effect, as long as you are consuming the normal doses one would encounter in 1-2 cups of morning joe.  So while you are having your big glass of water, you can be working to grind those beans and get the espresso machine fired up.

Eight cups of water per day!

Everyone knows this, right?  Well, I’d love for you to forget it.  This antiquated notion comes from a 1945 US government recommendation that was based on a grand total of zero research.  To be fair, there were a number of experts who agreed on this number, but we’ve learned a lot in the last 75 years.  Every individual actually has their own fluid requirement based on gender, body size, activity level, where they live, etc.  And your water intake is not limited to what you drink!  Food actually contains a good amount of water, and this counts toward your daily requirements.

All that said, many people do live in a continuously under-hydrated state.  You can probably handle more fluid (unless you have a disease like Congestive Heart Failure or End Stage Renal Disease).  One simple test of your hydration status is to look at the color of your urine.  It’s not a perfect test, but it’s a good place to start.  You want to see a stream that is light yellow or “straw colored”.  If it is dark or has a strong smell, you probably need to drink more water (or eat less asparagus).  When I’m at competitions with pro athletes, we will actually test the concentration of their urine in the morning, using this data to inform hydration recommendations for the day. If you are an active individual and you really want a daily goal, you probably need to be shooting for closer to 12-14 cups per day at the lower end.

What should I drink during the day?

Water works great.  It’s simple and easily available.  If you have a filtration system at home, you can take a full bottle with you to work.  But it’s fine to drink tap water in most places too.  You’ll want to be careful about levels of chemicals like chlorine though.  The tap water in our house actually has more chlorine than the water in our pool!  (That was prior to the installation of a filtration system.).  In general though, I’m not opposed to simple tap water.

Tea can be a great option as well.  Most juices and soft drinks should be avoided, but not for reasons of hydration.  That’s a separate topic.

There are companies like Nuun and Skratch Labs that make tablets and powders to add to your water during the day.  These add subtle flavor and electrolytes.  Such products can be a great addition, assuming they are not packed with sugar or sweeteners.  For some, the added taste is needed to encourage drinking.  The electrolytes and small amounts of carbohydrate can also improve the absorption of the fluid.  While certainly not a necessity, these can be nice to use.

That’s all great for daily hydration, but what about during exercise?

The best strategy for hydrating during exercise starts with being hydrated during the rest of your day.  So, all of that information on daily hydration is prerequisite for exercise hydration.  If you brush that off and just focus on drinking during your exercise session, I guarantee you will continue to fail.

If fluid needs vary for individuals at rest, I assure you they are more variable with exercise.  Those needs even vary within individuals depending on type of exercise, temperature, altitude, etc.  Given that, there are a few things you should focus on.

First, pay attention to thirst.  There are some experts who suggest simply drinking when thirsty is all you need to do.  It’s a simple recommendation, but the science behind it is complex.  Other experts suggest that if you wait until thirsty, you’ve already started down the road of dehydration.  For me, I’d say, “it depends.”  If you are thirsty, definitely drink.  But if you are thirsty, don’t assume that you’ve passed some dehydration threshold and all is now lost.  When you get the urge, take a nice big drink!  I think it also pays to have a strategy for hydrating though.  There are two tests that can help with constructing this strategy.

Athletes should periodically measure their sweat rate.  This is the amount of fluid they lose for a given activity.  Remember, this is dependent on the activity and the environment.  If you are going to run a half-marathon in May and the temperature is expected to be 75 degrees, you should test your sweat rate on a 1-2 hour run at about 75 degrees (give or take).  Here’s how it would work.  Weigh yourself (in kg!) prior to your run, then again immediately after your run.  Any weight loss, after accounting for fluid intake, can be considered fluid loss.  Yes, there is also glycogen loss which is significant, but this method yields a very reasonable estimate.  For each kg you lose, that is roughly 1L of water you did not replace.  Dr. Asker Jeukendrup, a Dutch physiologist, has a simple calculator for this on his website.  I recommend doing this test yourself!

Simply knowing your sweat rate isn’t enough though.  Just because you lose a liter of fluid in an hour doesn’t necessarily mean you need to drink an extra liter during exercise.  Athletes can lose 2-3% of their body weight in fluid losses without seeing a drop in performance.  For a 70kg athlete, that may mean they can drop to 68kg, losing 2L of fluid, without seeing performance detriment.  So don’t aim to replace every bit of your losses, but make sure you don’t drop too far.

Notably, over-hydration is much more dangerous than under-hydration.  Excessive fluid intake, even when those fluids contain electrolytes, can lead to dilution and a fatal condition called hyponatremia.  This is part of the rationale for drinking only when thirsty.  Some people will stick to a hydration plan at all costs, potentially drinking more than needed and suffering some dangerous consequences.  So I recommend knowing your sweat rate, but using it primarily as a general guideline.  You should also pay attention to your body.  Don’t force fluids for the sake of meeting a predetermined drinking schedule.  It also helps to have an informed estimate of how much fluid you will need for a given activity.  With that 2-3% body weight buffer, you have some room to play.

Should I drink water when exercising?  Do I need electrolytes and sodium?  How much sodium is enough?

Again…it depends.  (Don’t you love it!  Any other answer is blowing smoke though.)  It depends on the duration of the exercise, the environment, and the individual.  For shorter efforts, water is fine.  As the duration increases, so does the likelihood that sodium and other electrolytes are useful.  How much sodium should your drink include?  Of course, there are varying expert opinions here as well.  Some say that no extra sodium is needed, as your kidneys will regulate this perfectly.  Others are proponents of fairly large amounts of sodium.  For most people, a standard sports drink will do.  I’m not talking about Gatorade or Powerade here.  I’d rather you avoid those.  Instead, choose something with more natural ingredients, like Skratch Labs.  There is a minority of the population who tend to lose excessive amounts of sodium in their sweat.  For these folks, a sweat sodium test is warranted.  This test will quantify the amount of sodium lost in sweat, allowing individualized guidance on how much sodium an athlete should replace during exercise.  (This testing is offered at Knoxville Performance Lab.)

Wow…that’s a lot of talk about hydration.  If I had to boil it down to a few points, it would be these:

  • Make sure you get your daily, non-exercise hydration dialed in.  Use simple metrics like urine color to verify that you are on the right course.  Without that, the rest is a losing battle.

  • Every athlete should spend a little time determining their sweat rate in a few different conditions.  It doesn’t take much more than adding some pre- and post-exercise weights and a little math.

  • Use an electrolyte and carbohydrate drink mix for longer workouts.  If you have suspicions that you may be an overly salty sweater, have your sweat sodium tested.  It’s generally simple and relatively inexpensive.

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Kevin Sprouse