What is Sodium?

What is Sodium?

Sodium is an essential mineral that your body cannot make, so it has to come from food, and it works as the principal electrolyte in the extracellular fluid, the water and plasma that sit outside your cells. Chemically it is the element Na, a metal that in the body exists as the sodium ion, a single positive charge.

Almost all the sodium you eat arrives as sodium chloride, ordinary table salt, which is about 40 percent sodium and 60 percent chloride by weight. That is why a teaspoon of salt, roughly 5.75 grams, delivers about 2,300 milligrams of sodium, and why 1 gram of sodium equals about 2.5 grams of salt. Your body holds sodium in a tightly defended range: blood levels stay between 135 and 145 mmol/L even as intake swings from a low-salt day to a salty restaurant meal.

The kidneys do most of that defending, keeping or dumping sodium to hold the total amount steady. Sodium matters to anyone who trains because it is the electrolyte you lose most in sweat, far more than potassium or magnesium, and because it sets your blood volume, which feeds your working muscles and your blood pressure. Most people in Western diets eat too much of it, averaging around 3,400 mg a day, well above the amount the body needs, and the excess comes mostly from packaged and restaurant food rather than the salt shaker.

How it works

Sodium works by being pumped out of your cells against its concentration gradient, and that gradient is the battery that powers nerves and muscles. Every cell runs the sodium-potassium pump (Na-K-ATPase), which uses energy to push three sodium ions out for every two potassium ions it pulls in. This keeps sodium high outside the cell and potassium high inside, creating the electrical charge across the membrane called the resting potential.

When a nerve fires or a muscle contracts, sodium channels snap open and sodium floods inward, flipping the charge and sending the signal down the line; this is the basis of every heartbeat, every muscle contraction, and every nerve impulse. Sodium also drives absorption in the gut, because glucose and amino acids ride into cells on sodium cotransporters, the same mechanism that makes oral rehydration solutions work.

On the whole-body level, sodium controls fluid balance. Water follows sodium by osmosis, so wherever sodium goes, water goes, which means your total body sodium sets your blood and extracellular fluid volume. The kidneys police this constantly using hormones: aldosterone from the adrenal glands tells the kidney to reabsorb sodium and hold water, antidiuretic hormone (vasopressin) fine-tunes water reabsorption, and natriuretic peptides from the heart do the opposite, prompting the kidney to excrete sodium when volume runs high. When you eat more sodium than you lose, your body holds more water to keep the concentration normal, blood volume rises, and blood pressure can climb; this is the link between high salt intake and hypertension.

The formula

Sodium (mg) = salt (g) x 400 | Salt (g) = sodium (mg) / 400

Table salt is about 40% sodium by weight, so 1 g salt provides about 400 mg sodium and 1 g sodium equals about 2.5 g salt. Sweat sodium loss (mg) = sweat volume (L) x sweat sodium concentration (mg/L, typically 200 to 2,000).

How to apply it

• Anchor to the daily targets: The Adequate Intake for healthy adults is 1,500 mg of sodium per day, and health bodies set a general ceiling of 2,300 mg, the sodium in one teaspoon of salt. Most people already exceed this, so for general health the lever is cutting down, not adding.
• Cut sodium from packaged and restaurant food: About 70 percent of dietary sodium comes from processed, packaged, and restaurant meals, not the salt shaker. Reading Nutrition Facts labels, choosing lower-sodium versions, and cooking from whole ingredients moves your intake far more than skipping table salt.
• Pair sodium with potassium: Potassium blunts sodium's effect on blood pressure, so eating more fruit, vegetables, beans, and dairy while cutting salt lowers pressure more than either change alone. The DASH eating pattern is built on this high-potassium, lower-sodium balance.
• Replace sodium during long or hot exercise: For sessions over 60 to 90 minutes, especially heavy sweaters or hot conditions, aim for roughly 300 to 600 mg of sodium per hour, up to about 1,000 mg with heavy losses, using sports drinks, electrolyte tabs, or salted food alongside fluid.
• Match replacement to your sweat losses: Sweat sodium concentration ranges from about 200 to 2,000 mg per liter, so two athletes on the same run can need very different amounts. Salt marks on clothing, cramping, and salty-tasting sweat suggest a high loser who benefits from more sodium.
• Do not over-drink plain water on long efforts: Drinking large volumes of plain water during endurance events without replacing sodium can dilute blood sodium and cause exercise-associated hyponatremia. Drink to thirst and include sodium on efforts lasting several hours rather than forcing down water.

Types

Worked example

Say a runner weighs sweat losses on a hot 2-hour long run. They sweat about 1.2 liters per hour and their sweat sodium concentration measures 900 mg per liter, a fairly typical value. Here is what the sodium math looks like against a sports drink providing about 500 mg of sodium per liter.

This runner loses roughly 2,160 mg of sodium but replaces only about 600 mg, a shortfall of over 1,500 mg. On a single run the body buffers this, but across a hot week of training a heavy salt loser can add electrolyte tabs or salt food to close the gap and protect performance and cramping.

Sodium vs potassium

Sodium and potassium are a partnership: the sodium-potassium pump uses both to run every nerve and muscle, and their dietary balance drives blood pressure. Most people need less sodium and more potassium, which is exactly what the DASH pattern delivers.

By goal

• General health and blood pressure: Keep sodium under 2,300 mg a day, and closer to 1,500 mg if you have high blood pressure or are salt-sensitive. Cut it mainly by choosing less processed food, and lift potassium with fruit and vegetables. This combination lowers blood pressure meaningfully.
• Endurance and hot-weather athletes: You lose the most sodium of anyone. On efforts over 60 to 90 minutes take in roughly 300 to 600 mg of sodium per hour, more if you are a heavy or salty sweater, and match fluid to your sweat rate rather than drinking as much as possible.
• Strength and physique athletes: Do not fear normal sodium; it supports training performance, muscle pumps, and hydration. Keep intake steady rather than slashing it before a photoshoot, since sudden low sodium can flatten you and disrupt fluid balance more than it reveals definition.

Common misconceptions

• "All sodium is bad and you should cut it as low as possible." Sodium is essential; too little causes hyponatremia, fatigue, and cramping, especially in athletes. The problem is chronic excess. Most people benefit from cutting toward 1,500 to 2,300 mg a day, not from eliminating sodium, which the body genuinely needs.
• "Most of my sodium comes from the salt shaker." Only a small share, roughly 10 to 15 percent, comes from salt added at the table or in home cooking. About 70 percent is already in packaged, processed, and restaurant food before it reaches you, which is where cutting back actually moves the needle.
• "Sodium and salt are the same thing." Salt is sodium chloride, and it is only about 40 percent sodium by weight. So 1 gram of salt provides about 400 mg of sodium, and 1 gram of sodium equals about 2.5 grams of salt. Labels list sodium, not salt, so the numbers differ.
• "Drinking lots of plain water is always the safe choice on a long run." Over-drinking plain water during hours of endurance exercise can dilute blood sodium and cause exercise-associated hyponatremia, which is dangerous. On long efforts you need sodium with your fluid, and you should generally drink to thirst rather than forcing large volumes.

Related terms

Sodium FAQ

What does sodium do in the body?

Sodium is the main electrolyte outside your cells, and it controls fluid balance, blood volume, and blood pressure. It also powers nerve impulses and muscle contraction through the sodium-potassium pump, and it helps your gut absorb glucose and water. Every heartbeat depends on sodium moving across cell membranes.

How much sodium should I eat per day?

Healthy adults have an Adequate Intake of about 1,500 mg of sodium a day, and health authorities set a general upper limit of 2,300 mg, the amount in one teaspoon of salt. People with high blood pressure benefit from aiming closer to 1,500 mg. Most people currently eat around 3,400 mg.

What is the difference between sodium and salt?

Salt is sodium chloride, and only about 40 percent of its weight is sodium. So 1 gram of salt gives roughly 400 mg of sodium, and 1 gram of sodium equals about 2.5 grams of salt. Nutrition labels list sodium, not salt, so do not treat the two numbers as equal.

How does sodium raise blood pressure?

When you eat more sodium than you excrete, your body holds extra water to keep sodium concentration normal. That raises blood and fluid volume, which increases the pressure inside your arteries. Cutting sodium reverses this, and adding potassium-rich foods lowers pressure further, which is the basis of the DASH diet.

How much sodium do athletes lose in sweat?

Sweat sodium concentration ranges widely, from about 200 to 2,000 mg per liter of sweat, depending on genetics, sweat rate, heat, and fitness. Combined with sweat rates of 0.5 to 2.5 liters an hour, endurance athletes can lose several grams of sodium in a single long, hot session.

Do I need electrolyte drinks for a normal workout?

For most workouts under 60 to 90 minutes, plain water and a normal diet replace what you lose, so electrolyte drinks are optional. They matter for longer sessions, hot conditions, heavy sweaters, and back-to-back training days, where replacing 300 to 600 mg of sodium per hour supports performance and reduces cramping.

Can you have too little sodium?

Yes. Low blood sodium, called hyponatremia, causes nausea, headache, confusion, and in severe cases seizures. In athletes it usually comes from drinking too much plain water over hours of exercise without replacing sodium. Cutting dietary sodium far below need can also cause fatigue, cramping, and dizziness.

Does sodium cause water retention and bloating?

A high-sodium meal makes your body hold extra water temporarily, which can show up as bloating or a higher scale weight the next morning. This is normal fluid balance, not fat gain, and it resolves within a day or two as your kidneys excrete the excess sodium and water.

What foods are highest in sodium?

The biggest sources are processed and restaurant foods: bread and rolls, cured and deli meats, pizza, soups, sauces, cheese, chips, and fast food. Because sodium is added during processing, packaged foods contribute about 70 percent of intake, far more than the salt you add while cooking or at the table.

Should I cut sodium before a bodybuilding show or photoshoot?

Drastically cutting sodium before a photoshoot often backfires, because sodium and potassium balance drives how you hold water. Sharply dropping sodium can flatten muscles and cause rebound retention. Most coaches keep sodium and water steady rather than manipulating them aggressively, since the response is unpredictable and easy to get wrong.

References

1. Electrolytes. StatPearls, NCBI Bookshelf
2. Physiology, Water Balance. StatPearls, NCBI Bookshelf
3. Hyponatremia. StatPearls, NCBI Bookshelf
4. Baker LB. Sweating Rate and Sweat Sodium Concentration in Athletes: A Review of Methodology and Intra/Interindividual Variability. Sports Medicine, 2017. PMC5371639
5. Sodium intake for athletes before, during and after exercise: review and recommendations. Performance Nutrition (Springer), 2025
6. DASH diet to lower high blood pressure. MedlinePlus, U.S. National Library of Medicine
7. Salt and Sodium (intake limits, sources, and blood pressure). Harvard T.H. Chan School of Public Health, The Nutrition Source