What you need to know about hydration

Conventional wisdom recommends drinking 8 glasses of water per day to stay hydrated. Eight a day keeps the medic away.

Unfortunately, there’s no actual science behind this recommendation. To make matters worse, there’s no mention of electrolytes either. This is a glaring omission from the hydration conversation.

The dictionary, in case you were wondering, defines hydration as “the quality or state of being hydrated (especially: the condition of having adequate fluid in the body tissues).”

I like the “adequate fluid” part of the definition, because it hints at the REAL goal of hydration: To achieve a level of fluid balance conducive to optimal health and performance.

Balance is the operative word here. Balance means drinking a Goldilocks amount of water — not too much, not too little, just right. Balance also means getting enough electrolytes to keep your system humming along like a TAG Heuer.

Everyone needs to think about hydration. But certain folks — athletes, low carb dieters, and anyone who likes to sweat — need to think about it more than others. I’ll share my thoughts on how these groups should be hydrating near the end of the article.

First, though, I need to clear up some confusion about dehydration.

Should You Drink More Water To Prevent Dehydration?

Dehydration — defined as losing more water than you’re taking in — gets blamed for many conditions. Performance declines, muscle cramps, mood swings, heat stroke... the list goes on. Believe it or not, some medical “professionals” even blame dehydration for obesity and diabetes.

Here’s the thing. Most of this dehydration trivia is unsubstantiated.

Take heat stroke, for example. Most people who die of heat stroke (about 700 per year in the US) are either infants or senior citizens. These populations have physiologic issues cooling themselves via sweat. More fluids won’t fix that.

Additionally, dehydration doesn’t appear to raise core body temperature. In fact, when athletes are dehydrated, they stop activity at lower body temps. This lines up with data from MDAlert.com reporting that, in all the medical literature, there isn’t a single case of death from sports-related dehydration.

Still, dehydration is widely considered the scourge of athletes. Because of this, people take extreme measures to ward it off. For instance, one 2009 study published in the British Journal of Sports Medicine found that, in a sample of 197 runners, a large proportion reported drinking on a set schedule. In other words, they glugged liquid even when they weren’t thirsty.

This practice of overwatering, unfortunately, leads to a dangerously low sodium state called hyponatremia. And unlike simple dehydration, hyponatremia has been fatal to athletes.

The Need For Sodium

Sodium is an electrolyte — a mineral that carries electrical charges (read: nerve impulses) in your body. Sodium also regulates fluid balance, which is, if you recall, at the core of hydration.

When you don’t consume enough sodium, you may experience headaches, muscle cramps, fatigue, and insomnia. And when blood sodium levels fall below a certain point, it’s called hyponatremia.

Exercise-associated hyponatremia is more common than you might think, affecting about 15% of endurance athletes. The severely sodium-deprived athlete may experience seizures and brain damage. In the most severe cases, hyponatremia can be fatal.

Often, hyponatremia is often mistaken for basic dehydration, or not drinking enough water. However, encouraging someone with hyponatremia to drink more water dilutes blood sodium levels, making the problem worse. In one tragic case, an army trainee was overwatered, and subsequently perished from low sodium levels.

Common causes of hyponatremia include:

• Overwatering
• Excessive sweating (especially combined with overwatering)
• Heart failure
• Kidney disease
• Liver disease
• Cancer
• Vomiting
• Diarrhea
• Diuretic usage

All but the first two reasons are beyond the scope of this article. If you have one of the listed medical concerns, see a doctor. Overwatering, on the other hand, is more easily rectified.

Preventing Low Sodium

To maintain adequate sodium status — and therefore stay properly hydrated — there are two main strategies to follow:

1. Don’t drink too much water
2. Do consume enough sodium

The first pillar relies on a simple rule: Drink to thirst.

Thirst doesn’t happen by accident, but rather is governed by physiological triggers like osmolality and blood volume. Osmolality, in case you were wondering, is a fancy scientific term that refers to the amount of electrolytes in your blood. Higher osmolality, generally speaking, leads to greater thirst.

If you think about it, it makes sense. When you eat extremely salty foods, you get thirsty.

Decreasing blood volume also triggers thirst. If your blood takes up less space in your blood vessels than is advantageous or beneficial, it probably means you need more fluid.

The other pillar of healthy hydration is to consume adequate sodium. Did you know that athletes can lose up to 7 grams of sodium per day through sweat? That’s a solid three and a half teaspoons of salt.

The good news is, drinking salty liquids can prevent and reverse exercise-associated hyponatremia. This was shown in a 2014 randomized controlled trial, in which hyponatremic runners saw similar improvements from drinking a saline solution as they did from receiving IV sodium.

Do You Need Sugar For Hydration?

In 1960, Dr. Robert Crane proposed an interesting theory. Glucose and sodium, he believed, worked synergistically to enhance one another’s absorption through the gut.

His “co-transport hypothesis” has since been proven true. With the help of transporter proteins called SGLT1 and SGLT2 (primarily), sodium and glucose (along with water) are absorbed more effectively through the intestines than either substance by itself. This discovery has saved, by some estimates, millions of lives — mostly due to rehydrating victims of the bacterial infections, such as cholera.

But do you need glucose to absorb sodium and stay adequately hydrated? Not at all. Consider the following:

• Sodium can be absorbed without a cotransporter in the small intestine.
• Glucose isn’t the only sodium cotransporter. Butyrate, amino acids, phosphorus, potassium, chloride, and beta-hydroxybutyrate (ketones) also help absorb sodium.
• Without the help of glucose, a man maintained normal sodium levels throughout most of a 382 day fast.

Don’t get me wrong. I’m not anti-sugar for hydration — it has its place, especially when hydrating for endurance performance. But it’s certainly not necessary for day-to-day hydration.

Other Hydration Electrolytes: Potassium and Magnesium

After sodium and water, I consider potassium and magnesium to be next in line for hydration. Deficiencies in either electrolyte can cause headaches, low energy, and muscle cramps.

Potassium is especially important because it works synergistically with sodium to maintain fluid balance. If you don’t consume enough potassium, your body tries to restore this balance by selectively excreting more sodium. Unfortunately, this depletes sodium levels, which really compromises your hydration status.

Unlike sodium, you lose very little potassium and magnesium through sweat. Nonetheless, you’ll still want to optimize dietary sources to prevent deficiency. You can check out lists of electrolyte-rich foods to prioritize in your diet here.

When You Need A Hydration Strategy

Many people can stay hydrated by drinking to thirst, salting their meals, eating electrolyte-rich foods, and making up for any shortfalls with an electrolyte drink. Certain circumstances, however, call for more attention. These include:

• Exercising in warm climates. When you exercise in the heat, you lose considerable fluid and sodium through sweat (up to 7 grams per day). To prevent exercise-associated hyponatremia and dehydration, drink salty water to thirst.
• Exercising in the cold or at elevation. These conditions can make your thirst mechanism go haywire, and you may need more water than thirst dictates. Check out this article for strategies to hydrate in these circumstances.
• Swimming. Long distance swimmers have scant opportunities for drink breaks, so planning is key. Maybe stop every 10 laps to swig electrolyte water at the pool’s edge.
• Eating a low-carb diet. On a low-carb or keto diet, two forces push you towards sodium deficiency. The first is that whole foods diets are naturally low in sodium, and the second is that you urinate more sodium on a low-carb diet. Why? Because low-carb diets lower the hormone insulin, low insulin lowers the hormone aldosterone, and low aldosterone signals your kidneys to excrete more sodium via urine.

If you forget that factoid, don’t worry. Just remember that, in general, low carbers need more sodium.

Healthy Hydration Summary

Healthy hydration isn’t about drinking 8 glasses of water daily, but rather balancing fluid and electrolyte intakes to keep your body running smoothly. Here’s a quick recap of what we covered today:

• Dehydration gets blamed for many problems, but the bigger problem is drinking too much water.
• Overwatering dilutes sodium levels, resulting in headaches, cramps, fatigue, or worse.
• Sugar can help you absorb sodium and fluids, but it’s not essential for hydration.
• If you’re active in warm climates, exercise at altitude, or eat a low-carb diet, you’ll need a hydration strategy.

Running through this article is a common thread: When it comes to hydration, water alone doesn’t cut it. You need electrolytes too.

Science-backed targets you can aim for are 4–6 grams of sodium, 3.5–5 grams of potassium, and 400–600 mg of magnesium daily. Play around with your intake and find what feels best for you. You’ll feel the difference when you get it right.