🧂Your Body Has a Secret Salt Stash — And It May Change How We Think About Sodium<> 

Confession: sodium — how much we need or don't need during training and racing, as well as just in everyday life — confuses the heck out of me. I know it's important. Sodium is a vital electrolyte that helps regulate water balance and blood pressure, and helps maintain nerve function and muscle contraction. We need it for health, life, and performance.

But how much? Boy oh boy. That's a topic up for serious debate. We lose sodium when we sweat, so we need to have enough on board and adequately replace it during exercise. But how much we lose — and how much we need — varies tremendously between individuals, ranging from roughly 200 milligrams to over 2,000 milligrams per hour. Taking in too much or too little can leave you feeling bad.

How much do you need in daily life? Another great question. According to a paper published earlier this year in Exercise and Sport Sciences Reviews, the U.S. Dietary Guidelines recommend no more than 2,300 mg of sodium per day, while the American Heart Association’s optimal goal is no more than 1,500 mg daily. And yet, nine in ten American adults exceed these guidelines, averaging roughly 3,550 mg/day.

Some experts recommend sweat testing to sort all this out, which makes logical sense... until you learn that what we thought we knew about how sodium moves and is stored in the body may very well be outdated and incomplete. It's a discovery that could change the way we approach all things sodium. (Credit where it's due: I first went down this rabbit hole via a great Fast Talk episode.)

The old model: whatever you lose, you must replace

For decades, physiology taught that sodium lives in two places — the blood in your vessels and the fluid around your cells — and that these spaces stay locked in balance. Lose salt in sweat or urine, the thinking went, and you had to replace it (along with fluids), or your blood volume and blood pressure would drop.

Then researchers found a secret sodium stash

Our understanding of this shifted when a research team using ²³Na-MRI to directly image sodium in living tissue found something the old model couldn't explain: skin and muscle store substantial amounts of sodium bound to proteins in the tissue, without pulling water along with it the way you'd expect. Think of it as a holding tank. Eat more salt, and immune cells in your skin trigger new lymphatic-vessel growth to help store — and later drain — that sodium.

What sweat testing can (and can't) tell you

This is where sweat testing gets complicated. A standard sweat test — usually a patch on your forearm or back — gives you one number: how salty your sweat was at that spot, on that day, under those conditions. Used narrowly, that number has one job: helping you estimate roughly how much fluid and sodium you're losing per hour in a given effort, so you can match your drink mix and fluid volume to a specific event instead of guessing from a generic chart. 

I called up Kristen Arnold, MS, RDN, CSSD, Team Nutritionist for EF Pro Cycling, to see how she thinks about sodium with the athletes she counsels— and her starting point is pretty simple. 

"When working with athletes, I regularly use free, easy sweat-volume tests to establish a baseline," she says. "Sodium concentration testing isn't always necessary unless they're training/racing more than two hours or showing signs of high sodium losses, such as visible salt deposits on clothing/skin or very high sweat rates."

But even when concentration testing is warranted, you don’t want to lean too hard on a single number. First, sweat sodium concentration can vary by 80 to 120% across different sites on the same person's body. So, a single forearm patch is a rough estimate of one region, not a precise readout of your whole-body losses. It’s also a fixed number. It can shift day to day with heat, intensity, and hydration status, as well as over the course of a season.

"An athlete's sweat sodium concentration can significantly change with heat training or heat acclimation," Arnold says. "A sweat sodium test you had done in the spring will need to be adjusted or retested after heat acclimation in mid-late summer. Some of the athletes I have tested multiple times can change by up to 50% sweat sodium concentration."

It also can't tell you exactly why your number is high — and this is where the third compartment may change the interpretation. The old, two-compartment model said a "salty" result means one thing: you're losing sodium fast, so replace it aggressively. But your sweat glands don't pull sodium straight from your bloodstream — they draw their precursor fluid from the local interstitial environment in your skin, the same dermal "holding tank" where excess dietary sodium gets stored. Load that tank up with a high-sodium diet, and the fluid your sweat glands draw from is more concentrated to begin with — measurably so,  as people on a high-sodium diet run higher sweat sodium than the same people on a low-sodium diet.

So a "salty sweater" result may be less about how much sodium your body is shedding and more about how full your skin's storage tank already is — evidence you're getting plenty, not proof you need more. (To be fair, researchers are still working out how much a given bout of sweating actually draws down that stored reservoir versus simply reflecting it — this is an active, not fully settled, area of study.) Either way, a sweat test delivers a number without telling you if it’s true high loss, or a full tank spilling out. 

Why sodium may matter more after menopause

These distinctions matter for our general health, especially as we enter the menopause transition. When we have more stored sodium than we can clear, we can experience salt-sensitive blood pressure spikes. And salt sensitivity itself rises sharply after menopause. Estrogen normally helps the kidneys dump sodium when blood pressure climbs. As estrogen falls, that protection fades, and women's hypertension rates catch up to or exceed men's. 

What it means for your sodium intake

In my mind, this all means not going overboard on sodium, even if you’re an endurance athlete. On a daily basis, a 2025 review found no evidence athletes need more sodium than anyone else; your kidneys and sweat glands already handle routine losses without extra help.

During exercise, research generally recommends endurance athletes consume 300 to 600 mg of sodium per hour for efforts over two hours, scaling up in heat. (There's no solid evidence tying sodium directly to muscle cramps, by the way — those appear to be multifactorial, not simply driven by an electrolyte deficit.)

The one place sodium loading does have real scientific support: the hours before a long, hot race. An acute sodium dose pre-exercise expands plasma volume, boosts fluid retention, and has improved performance in heat. That's a smart move before a long, hot race or training session, not a reason to load up on sodium every day. I also highly recommend working with a certified sports dietitian to dial in your personal needs.