Sodium Isn't Just for Cramps: How Much You Actually Need (and Why)
February 27, 2026 — 9 min read
Your sodium target is set by your sweat rate and the temperature you're working in, not by how many carbs you're taking. Most endurance athletes land somewhere between 500 and 1,500 mg/h at baseline; heat scales that up on a five-tier curve, capped at 1,500 mg/h. Sodium is mostly about replacing sweat losses and keeping your plasma volume where it needs to be so the rest of your fueling can work.
Sodium isn't a cramp thing. It's a sweat-replacement and plasma-volume thing.
A heavy sweater on a hot day can shed more than a gram of sodium per hour through sweat alone. Once you're behind on replacement, plasma volume drops, your sweating becomes less effective, your heart has to work harder to deliver the same oxygen, and the rest of your fueling plan starts to wobble. None of that is about your calves cramping at mile 22, although getting the sodium math right may help with that too.
The salt-prevents-cramps story isn't wrong. It's incomplete. Sodium does more important work earlier in the timeline, and that's the work this article is about.
What sodium actually does
Sodium does several things during endurance work, ranked roughly by how much they matter on the day.
It replaces what your sweat takes out. Sweat is between roughly 200 and 1,500 mg of sodium per liter, with most endurance athletes landing in a band you can map onto a sweat-type baseline (more on that below). Heavy sweaters working hard in the heat can cross 1.5 liters per hour. The losses are real and they add up fast.
It maintains your plasma volume. Sodium is the main electrolyte that holds water in your bloodstream. When plasma volume drops, two things you care about get worse at the same time: your heart has to work harder to deliver the same oxygen (cardiac drift), and your skin gets less blood for cooling. Sodium replacement keeps the system propped up.
It protects against the dilution problem. Drinking a lot of plain water on a long, hot day pushes plasma sodium down, not up. In its severe form this is exercise-associated hyponatremia, and it's the dominant medical risk in long endurance events. More on this in the section below.
It probably helps some people with some kinds of cramping. The cramping literature is genuinely mixed. Some cramps respond to sodium. Others are neuromuscular fatigue and no amount of salt fixes them. "Sodium prevents cramps" is too simple, but "sodium has nothing to do with cramps" is also too simple.
A NOTE ON ABSORPTION
PODIUM calculates sodium and carbs as two independent prescriptions. Coupling them (raising sodium whenever carb intake rises) is a defensible-looking alternative that the SGLT1 stoichiometric argument supports on paper. PODIUM doesn't apply that coupling, and the call is deliberate.
The SGLT1 transporter that pulls glucose through your gut wall does need sodium to work. The catch is the sodium isn't consumed in the process. It recycles. And your gut already secretes about 18 grams of sodium per day through bile, pancreatic juice, and other digestive fluids. That endogenous pool dwarfs what SGLT1 actually demands at any carb rate you'd realistically run.
Direct experimental work (Gisolfi 1995, Jeukendrup 2009, Fordtran 1967) found that varying beverage sodium across a wide range produced no meaningful change in fluid or glucose absorption. The GSSI's own 2023 review put it plainly: beverage sodium plays only a minor role in intestinal absorption because the gut supplies its own.
So PODIUM's engine runs sodium and carbs as independent calculations. Your sodium target is set by what you're losing through sweat, not by what you're eating. Coupling them would be more complicated and less correct.
When does sodium matter?
Under 60 minutes, you don't really need to think about it. Your body has enough sodium on board to handle a shorter effort without intentional replacement.
The exception is heat. If it's hot, even a 45-minute run can leave you sweating enough that some sodium helps. Heat compresses the timeline.
Past 60 minutes (or sooner in warm weather), sodium should be part of your plan. Pair it with a consistent timing rhythm for your fuel and you've got the basics covered.
The simple rule: if you're fueling for the duration, you're fueling sodium too.
NOTE
If you're doing a 45 to 60 minute workout and taking in some carbs (which you should be, even if just for gut training), the fuel itself probably has sodium in it. Most gels and drink mixes do. So you're covered without thinking about it. The "under 60 minutes, don't worry about sodium" rule assumes you're not going out of your way to add extra, not that you're avoiding it entirely.
Find your sodium baseline
Three sweat types. The biggest variable is how salty your sweat is, and that varies a lot from person to person. You can identify yours from your kit after a long or hard session:
- Low sweater (~500 mg/h). You rarely see salt stains on your gear or skin. Your sweat is there, but it doesn't leave much behind.
- Moderate sweater (~1,000 mg/h). You notice some salt marks on your hat, shirt, or skin after longer or more intense efforts. Nothing crazy, but it's visible.
- Heavy sweater (~1,500 mg/h). There's grit on your face when you wipe it. Heavy white crust on your kit. Your eyes sting when sweat runs into them. People have probably commented on it.
Your Sodium Baseline (mg/h)
~500 mg/h
Low Sweater
No salt stains
~1,000 mg/h
Moderate Sweater
Some salt marks
~1,500 mg/h
Heavy Sweater
White crust on kit
No lab test required. If you've done a few long runs or rides, you already have the data, it's on your clothes.
Start with the baseline that matches your sweat type. That's your hourly target for cool-weather efforts past 60 minutes.
Heat scales it on a curve
Heat doesn't just make you sweat more, it makes your sweat saltier. As sweat flow rises, sodium secretion outpaces reabsorption, so the concentration goes up alongside the volume (Buono 2007). Both effects compound. A 95°F day isn't 1.25× a 78°F day on the sodium side; it's something closer to 1.5×.
PODIUM applies a five-tier multiplier to your sweat-profile baseline based on the forecast temperature:
- Cold (below 59°F): 0.85×
- Cool (59 to 72°F): 1.00× (baseline)
- Warm (72 to 82°F): 1.25×
- Hot (82 to 91°F): 1.50×
- Very Hot (above 91°F): 1.75×
A hard cap of 1,500 mg/h applies after the multiplier. Beyond that, the prescription gets hard to drink and starts driving over-consumption of fluid, which is the bigger risk anyway.
Full breakdown of the curve, the cap, and the practical adjustments lives at Fueling in the Heat.
The mistake to avoid
When people hear "take more sodium," they often follow it with "drink more water."
Makes sense on the surface. But more sodium plus much more water can actually make things worse.
If you take in a lot of plain water without enough sodium, you dilute what's already in your blood. Plasma sodium drops, you feel foggy and bloated, and in extreme cases you end up worse off than if you'd done nothing. This is exercise-associated hyponatremia. It's more common than people think, especially in longer races where aid stations are everywhere and nerves drive over-drinking. Across studies of ultra-distance events, the dominant risk factor for hyponatremia turns out to be fluid intake exceeding losses, not sodium intake being too low (Hoffman & Stuempfle 2015; Hew-Butler 2017).
Think of it like mixing a sports drink. If the instructions say one scoop per 16 ounces, and you put in the scoop but fill it with 32 ounces of water, you've got a weak, diluted drink that doesn't do its job. Same thing happens in your body.
Drink to thirst, not to a schedule. Replace sodium based on your sweat profile and the conditions. Let the ratio take care of itself.
How PODIUM handles this
You tell the app your sweat profile (low, moderate, or heavy) and your sport. PODIUM pulls the forecast for your workout, applies the five-tier heat multiplier to your baseline, and applies the 1,500 mg/h cap. The number you see on the Plan tab is your hourly sodium target for that specific session.
Worked example: moderate sweater (1,000 mg/h baseline), 95°F race day, 90-min Z3 tempo.
Sodium track: baseline = 1,000 mg/h heat tier = Very Hot (>91°F) multiplier = 1.75× raw target = 1,750 mg/h cap check = 1,750 > 1,500 → clamped prescription = 1,500 mg/h Carb track (constraint model, sex-agnostic, heat-agnostic): research target = 60 g/h capacity = 65 g/h sport ceiling = 90 g/h floor = 20 g/h prescription = 60 g/h, research target wins
Two prescriptions, no trade-off. The Plan tab shows both. The carb side runs on its own constraint model in parallel: higher carbs don't pull sodium up; higher sodium doesn't pull carbs down. They're independent because the underlying physiology is. The full breakdown of how the engine picks the carb number lives at How Many Carbs Per Hour.
For the deeper mechanics of how the engine assembles a fueling plan, see How PODIUM's Algorithm Works.
Frequently asked questions
Bring it home
Sodium isn't a cramp thing. It's a sweat-replacement and plasma-volume thing. The math is set by how salty you sweat and how hot it is. Carbs don't enter the equation.
Figure out your sweat type. Trust the heat curve. Drink to thirst. The rest takes care of itself.
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The First Marathon Fueling Protocol
The exact fueling blueprint to execute your first 26.2 miles with zero guesswork.
- •Carb & sodium guidelines
- •Race week and race day fueling timeline
- •Gut training program
