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The Science of Electrolytes for Ultra-Active People

(What Are They & Who Needs Them)

When it comes to electrolytes, athletes, soldiers, firefighters and others who engage in vigorous, prolonged physical activity have a unique challenge. In a word, they sweat, and it can be a lot. The result is a double whammy because exercise-induced sweating can not only lead to excessive fluid loss, but it can also wash out key electrolytes.

Replenishing this electrolyte loss during rehydration is a big deal, especially if the goal is to maintain peak performance during activity, stay mentally focused and recover fast.

Plus, the body is unable to make them, so we need to get electrolytes from the foods and supplements we consume.

Why electrolytes are so special

When electrolytes are dissolved in watery fluids like blood and other body fluids, they become ions that have the ability to hold an electric charge. Some hold a positive charge (cations), while others hold a negative change (anions). In this form, they can move across cell membranes as needed to perform a variety of biochemical functions.

Electrolytes allow your nerves to communicate, your heart to pump and your muscles to contract. They keep your body’s pH level in the normal range (acid-base balance) and maintain osmotic equilibrium. Electrolytes also play a critical role in your body’s ability to maintain proper fluid balance.

Why your sweat rate matters

Every active person needs to know about electrolytes that are lost in sweat and how to replenish them. Why? Exercise, especially in warmer weather, can double the amount of fluid that a typical athlete loses over the course of a day. And, this uptick in fluid loss is mostly due to sweating.

Here’s a breakdown of five key electrolytes lost in sweat, and how to replenish them:

1. Sodium

Sodium is the body’s major cation in the fluid surrounding cells (extracellular fluid). Here, it regulates the size of the compartment and plasma volume. Sodium also plays a role in nerve and muscle function.

Sodium loss in sweat is reported to be highly variable, ranging from as little as 460 mg to as much as 1,840 mg in every liter of sweat. People who perform activities in hot, humid conditions, people who have a high sweat rate (more than 1.2 liters per hour), and people who are “salty sweaters” tend to lose the most sodium in their sweat. If you typically see a white residue on your skin and clothes after activity, you’re likely a salty sweater. It’s the dry salt (sodium chloride) that remains after your sweat has evaporated.

Table salt is the most common food source of sodium with about 600 mg per serving (one-quarter teaspoon). For this reason, training tables often include salty snacks like pretzels, jerky, trail mix, popcorn and pickles.

2. Chloride

Chloride is the major anion in extracellular fluid. It works with sodium to maintain water balance and osmotic equilibrium.

Like sodium, chloride losses in sweat are highly variable and are reported to range from 710 mg to 2,840 mg per liter of sweat. Exercise typically increases chloride needs, and this is especially true for those who exercise in the heat.

Table salt is also the main food source of chloride with about 900 mg per serving (one-quarter teaspoon). This is another reason you often see salty snacks on training tables.

3. Potassium

Potassium is the major cation inside cells (intercellular fluid). Along with sodium, potassium plays a role in water balance, osmotic equilibrium and acid-base balance. It’s also needed for neuromuscular activity and cell growth, including muscle cells.

The loss of potassium in sweat is less variable than that for sodium and chloride. It’s reported to range from 160 mg to 320 mg per liter of sweat, and people who have a higher sweat rate may lose more.

Potassium is found in a wide variety of foods. Fruits like apricots, bananas, raisins and prunes are excellent sources. Other good food sources are vegetables, legumes, meats, poultry, fish, milk, yogurt, nuts and brown rice.

4. Magnesium

Magnesium is another major intracellular cation (second only to potassium). It plays a key role in bone health, muscle and nerve function, heart health and energy production. It also allows your body to produce a wide variety of bioactive compounds.

The loss of magnesium in sweat is reported to be low and relatively constant, ranging from 0 mg to 36 mg per liter of sweat. Exercising in hot environments tends to increase magnesium needs.

Magnesium is available in a wide variety of foods, but the richest sources are plant foods, including dark green vegetables, seeds, nuts, legumes and whole grains. Other food sources include fish and milk.

5. Calcium

Most of the calcium in the body resides in bones and teeth, but about one percent is found in body fluids (mostly extracellular fluid). Here it’s a cation that supports muscle and nerve function, promotes heart and blood vessel health, and regulates hormone and enzyme activity.

Like magnesium, the loss of calcium in sweat is relatively low and constant, ranging from 0 mg to 120 mg per liter of sweat. People who consistently exercise in the heat are prone to lose more calcium in their sweat, so they may have a greater need to replenish.

The most common food sources of calcium are milk, yogurt and other dairy products. Other good food sources include kale, spinach, broccoli and other dark green, leafy vegetables as well as canned fish, almonds and beans.

The bottom line

Whether for work or sports, when you push your physical performance to the edge day after day, it can take a toll on your electrolyte balance. To help you replenish and recover fast, you’ll need a smart strategy.

Here’s an easy 3-step plan that can help. First, include electrolyte-rich foods in your daily meals. Next, keep a few salty snacks handy for pre- or post-activity snacking. Finally, add a balanced electrolyte tablet like Replace™ Electrolyte to your training routine to help ensure you replenish key electrolytes you lose in sweat. Simply drink water to quench your thirst.

The sooner you start, the sooner you’ll have the support you need to take on – and recover from – the unique demands of your ultra-active lifestyle.


Karpinski C, ed. Sports Nutrition Manual, A Handbook for Professionals. 6th ed. Chicago, IL; Academy of Nutrition and Dietetics; 2017.

Ross AC, Caballero B, Cousins RJ, Tucker KL, Ziegler TR, eds. Modern Nutrition in Health and Disease. 11th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2014.