Am I a salty sweater? How to tell, and what to do about it

Are you a salty sweater? If your kit, cap or helmet straps dry with a white, gritty crust after a long session, and your sweat stings your eyes or tastes sharp on your lips, you probably sit towards the salty end of the range. That is worth knowing, but it is a reason to plan a bit more sodium into long and hot sessions, not a reason to start swallowing salt tabs on every run.

I'll be straight about the evidence, because a lot of what gets written about salty sweaters comes from companies selling the fix.

What "salty sweater" actually means

Everyone loses sodium in sweat. What differs is how much sodium is in each litre. In a study of 506 athletes across endurance and team sports, whole-body sweat sodium averaged about 36 mmol per litre, with a range from roughly 18 to 71 mmol per litre. In plain numbers, that is around 830mg of sodium per litre on average, from about 420mg at the low end to about 1,630mg at the top.

So a "salty sweater" is just someone near the top of that range. Their sweat carries close to four times as much sodium per litre as the least salty athletes. Put that together with a high sweat rate and the hourly losses get big fast, which is where it starts to matter for performance and for how you feel in the last hour of a long day.

The signs, and how much to trust them

These are the clues athletes and coaches use. I've added how much weight I'd give each one.

One honest note. I could not find a peer-reviewed study that checks whether these signs actually line up with measured sweat sodium. The idea that "three or four signs means you're salty" comes from hydration companies, not independent research. I still think the white crust is a useful clue, because you can see the salt with your own eyes, but treat the rest as supporting evidence, not a diagnosis.

If you want a real number, a sweat patch or lab test measures your sweat sodium directly. It costs money, and for most age-groupers it is not necessary. If the white marks are obvious every time, you already know the answer that matters: plan for the top end.

Saltiness changes with heat

Your sweat is not fixed. Heat acclimation lowers sweat sodium concentration, and it happens quickly. In a study of workers tested in summer and in winter, sweat sodium had already dropped by the second day of working in summer heat, and that drop did not happen in the cooler winter tests. A large review of sweat testing lists heat acclimation alongside intensity, environment, fitness, diet and hydration as things that shift both sweat rate and sweat sodium.

This is why the first hot week of the year feels so rough, and why a triathlete who flies from a cool spring into a hot race abroad is likely to lose more salt per litre than they would after a summer of training in the heat. Your crusty kit in April may be crustier than your kit in August.

What about cramps?

This is the big one, and it is where the salt-tab marketing oversells. A lot of athletes who call themselves salty sweaters started taking salt because of cramps. The evidence that sodium prevents exercise cramps is weak.

In a 161km ultramarathon run in heat up to 39°C, runners' sodium intake ranged from about 2,500mg to over 38,000mg across the race. Sodium intake was no different between the runners who cramped and those who did not. It was a small study, 20 runners with full food records, but it is a useful reality check. Cramping in long events seems to have more to do with fatigue and how hard you're pushing than with salt alone.

So if cramp is your only sign, I wouldn't assume you're a salty sweater. Look at your pacing and your training first.

Where it does matter

None of that means sodium is pointless for salty sweaters. Two findings are worth knowing.

In a study of 51 marathon runners classed by sweat patch as low, typical or salty sweaters, sweat sodium loss influenced blood sodium after the race. Even so, none of the salty sweaters developed hyponatremia. The saltiest runners lost the most and finished with lower blood sodium, but the bigger danger in long events is still drinking too much plain fluid, not losing too much salt.

In a randomised trial in a half-ironman, 26 triathletes took either salt capsules or a placebo, adding up to 2,580mg of sodium across the race for the salt group. The salt group finished faster and had higher blood sodium at the finish. The authors put it down mostly to the salt group drinking more and holding their fluid better.

My take from all of it: for salty sweaters, extra sodium earns its place in long sessions, hot sessions, and anything over about two hours. On a one-hour run, a club ride or an hour in a cool pool, it barely matters.

What to do if you are one

Here is the practical version.

1. Work out your sweat rate first. Weigh yourself before and after a session, add what you drank, and divide by the hours. Our sweat rate guide walks through it. A salty sweater with a low sweat rate loses less sodium than an average sweater who pours.

2. Assume the top end for saltiness. If you've got obvious white crust, plan as if your sweat is towards 1,600mg per litre rather than 800mg. Multiply that by your sweat rate to see your rough hourly loss. The sodium per hour guide has worked examples.

3. Replace part of it, not all of it. You do not have to put back every milligram in real time. A stronger electrolyte drink, salty food on the bike, or capsules on long hot days will close the gap without the bloating.

4. Never chase it with extra water. Drinking more than you sweat is how people end up with dangerously low blood sodium. Salt doesn't fix overdrinking. Our hyponatremia guide covers why.

5. Practise it in training. Use the same drink and the same salty foods on your long rides, long runs and bricks that you'll use on race day.

Swimmers are a special case. You sweat in the pool and in open water, you just can't see it. A long open-water swim in warm water or a wetsuit can still leave a salty sweater short before the bike even starts, so plan sodium into what you drink before and between swim sets.

FAQ

Is being a salty sweater genetic? You'll see that claim a lot. I couldn't confirm it from an independent study for this article, so I won't state it as fact. What is well documented is that heat acclimation, diet and fitness all change how salty your sweat is.

Do salt tablets stop cramps? The best field data says no. In a hot ultramarathon, how much sodium runners took made no difference to who cramped.

Should I eat more salt day to day? For most athletes, normal food already carries plenty of salt. The planning matters during long and hot sessions, not at every meal.

Can I be a salty sweater and a light sweater? Yes. Saltiness is the concentration, sweat rate is the volume. You need both to know your loss.

Sources

• Baker LB et al. (2016). Normative data for regional sweat sodium concentration and whole-body sweating rate in athletes. Journal of Sports Sciences 34(4):358-368.

• Baker LB (2017). Sweating rate and sweat sodium concentration in athletes: a review of methodology and intra/interindividual variability. Sports Medicine 47(Suppl 1):111-128.

• Bates GP, Miller VS (2008). Sweat rate and sodium loss during work in the heat. Journal of Occupational Medicine and Toxicology 3:4.

• Hoffman MD, Stuempfle KJ, Valentino T (2015). Sodium intake during an ultramarathon does not prevent muscle cramping, dehydration, hyponatremia, or nausea. Sports Medicine Open 1:39.

• Lara B et al. (2017). Sweat sodium loss influences serum sodium concentration in a marathon. Scandinavian Journal of Medicine and Science in Sports.

• Del Coso J et al. (2016). Effects of oral salt supplementation on physical performance during a half-ironman: a randomized controlled trial. Scandinavian Journal of Medicine and Science in Sports 26:156-164.

MOVE's sweat test works out your own sweat rate and an hourly sodium estimate, and you can set fluid and sodium per hour on each planned session. The estimate uses an average sweat saltiness, so if the signs above fit you, treat its sodium number as your floor and plan upwards from there.