Electrolytes: who actually needs them?

Some athletes lose nearly four times as much salt in their sweat as others. Most people on most days don't need a powder at all.

Electrolyte powders and drinks have moved from the sideline to the office desk. The pitch is usually that most people are under-hydrated and plain water isn't enough.

The research supports a narrower claim. Some people, in some situations, lose enough sodium for it to matter. Most people, most of the time, get more than enough from food.

What you actually lose in sweat

Sweat is mostly water, plus sodium and chloride, the two parts of table salt. It also contains small amounts of potassium, calcium and magnesium, but sodium is the one lost in quantities that can matter.

How much varies a lot. A 2016 study of 506 athletes estimated whole-body sweat sodium at an average of about 36 mmol per litre, with individuals ranging from about 18 to 71.¹ In everyday units:

The same study found sweat rates averaging 1.2 litres per hour, but ranging from about 0.3 to more than 5.¹ Multiply a high sweat rate by a high sodium concentration and two athletes in the same session can lose very different amounts of salt.

Everyday life: food already covers it

The FDA puts average US sodium intake at about 3,400 mg a day, well above the 2,300 mg limit in the Dietary Guidelines.² For someone who isn't sweating heavily, sodium shortfall is rarely the problem. Adding a high-sodium electrolyte mix to an ordinary office day mostly adds to an intake that's already high.

Who does benefit

The case for electrolytes gets stronger as sweat losses go up:

• Long sessions, roughly two hours or more, especially endurance events.
• Heat and humidity, where sweat rates climb.
• Heavy or salty sweaters. White, gritty salt marks on dark clothing after training are a common practical sign.
• Two sessions a day, or tournaments, where there's little time to replace losses with meals in between.
• Physical work in the heat, over long shifts.

The ACSM position stand on exercise and fluid replacement notes that drinks containing electrolytes and carbohydrate can help sustain fluid and electrolyte balance and performance during exercise.³ Its emphasis is on individual needs, which depend on the numbers above.

What electrolytes don't do

They don't make over-drinking safe

Exercise-associated hyponatremia, dangerously low blood sodium during long events, is mainly caused by drinking more fluid than you lose. The 2015 international consensus statement names sustained, excessive intake of water, sports drinks or other fluids as the major risk factor.⁴ Most sports drinks contain far less sodium per litre than blood does, so drinking large volumes of them can still dilute it. Volume is what matters most.

They probably aren't the main fix for cramps

Exercise cramps are widely blamed on salt loss. The evidence is weaker than the belief. A review in the British Journal of Sports Medicine found the salt-and-dehydration explanation rests mostly on anecdotes and small case series, and that prospective studies haven't supported it. The better-supported explanation is neuromuscular fatigue.⁵ Some salty sweaters may still find sodium helps, but it isn't a general cure.

To find the first number yourself, see How to measure your sweat rate with a bathroom scale.