How Much Sodium Do Runners Need Per Hour?

For runs under about two hours, most runners need no planned sodium per hour at all; normal meals cover it. Running longer in Malaysian heat, a sensible starting range is roughly 200 to 550 mg of sodium per hour, and only ultra runners who sweat heavily, sweat salty and drink a lot need to plan for more.

That range isn’t plucked from a sachet label. It comes from the American College of Sports Medicine’s fluid guidance, and the rest of this guide shows where it bends for you: race length, how much you drink, whether you pre-load, and how to count sodium from salt caplets, tablets and drinks.

Why is there no single sodium-per-hour number?

Because the amount you lose and the amount you need to replace are two different numbers. In the largest sweat-testing dataset we know of, the Gatorade Sports Science Institute’s analysis of 1,303 athletes, endurance athletes lost about 1,190 mg of sodium an hour on average, with one standard deviation spanning roughly 550 to 1,830 mg (Barnes et al., 2019). We broke those numbers down in How Much Sodium Do You Lose Running in Malaysian Heat?

Replacement is a separate question. Sports dietitian Alan McCubbin modelled how much sodium athletes need to keep blood sodium stable, across sweat rates of 0.5 to 2.5 litres an hour and sweat sodium of 20 to 80 mmol per litre. Two things drove the answer: how much of your sweat loss you drink back, and how salty your sweat is. For an elite marathon, replacing sodium was unnecessary in every realistic scenario. For a 160 km ultra, runners with sweat sodium of 40 mmol per litre or more who drank back over 80% of their losses needed to replace at least 47% of the sodium they lost (McCubbin, 2022).

Put simply, the more water you drink over a long day, the more the sodium in that water matters.

Where does 200 to 550 mg per hour come from?

It comes from drink composition. The ACSM position stand on fluid replacement suggests sports drinks carry about 20 to 30 mmol of sodium per litre, around 460 to 690 mg, and gives 0.4 to 0.8 litres an hour as a starting point for fluid intake, adjusted to the individual (Sawka et al., 2007). Multiply the two and you land between roughly 180 and 550 mg of sodium an hour.

Treat that as the middle of the road. A small runner on a cloudy Fraser’s Hill morning sits at the bottom. A big, salty sweater grinding through the afternoon at a Sabah ultra can sit well above it.

How much sodium per hour by race length

The middle rows are where most runners argue with each other. Our view: if you’re out for more than four hours and drinking plain water by the cup at every station, plan some sodium. If you’re drinking to thirst and finishing a little lighter than you started, you have more room than the internet suggests.

What changes in an ultra?

In an ultra, sodium planning earns its place, but drinking too much is still the bigger danger. At the 161 km Western States Endurance Run, 93.9% of runners in one study used sodium supplements. The finishers who developed low blood sodium had taken sodium at the same rate as everyone else; what set them apart was overhydration, and none of them had lost more than 4.3% of their body weight (Hoffman and Stuempfle, 2015).

A five-year analysis from the same races found exercise-associated hyponatraemia in 15.1% of finishers overall, and it was more common in hotter years (Hoffman et al., 2013). The authors’ conclusion is one we’d pin to every Malaysian ultra drop bag: excessive sodium supplementation and drinking beyond thirst are both ill advised.

So for the 75K at Janda Baik Ultra or a long day at Borneo Ultra Trail, the practical order is:

1. Get your fluid right first. Drink to thirst, and know your sweat rate from training.
2. Then size your sodium to the fluid you actually take in.
3. Spread it across every hour, not in a handful at the checkpoint where you finally remember.

Aid stations on Malaysian trail ultras can be two or three hours apart on the climbs. A per-hour plan you carry with you beats a per-station plan you have to guess at.

Should you sodium-load before a race?

Pre-race sodium loading has some evidence behind it in heat, but it’s a tool to test, not a default. In a small New Zealand study, eight trained runners drank about 10 ml per kg of body weight of a very salty drink (164 mmol of sodium per litre) in portions over the hour before a run at 32°C. Compared with a low-sodium drink, plasma volume rose about 4.5%, core temperature ran lower and they lasted longer before stopping (Sims et al., 2007).

For a 60 kg runner that dose works out to roughly 2,200 mg of sodium in 600 ml of fluid. It is not pleasant to drink, and eight men in a lab is a thin base for a race-morning ritual. Sports Dietitians Australia’s position statement on exercise in heat says pre-exercise sodium loading “may be desirable in some scenarios” (McCubbin et al., 2020). We’d read that as: worth trying before a long, hot race you’ve trained for, never for the first time on race day.

A gentler version works for most people. Have a properly salted dinner the night before and a normal breakfast with a drink, rather than chasing litres of plain water at 4 am. If you’ve been told by a doctor to watch your salt intake, ask them before trying any of this.

Salt caplets, tablets or drinks: how do you count them?

Count milligrams of sodium, not milligrams of “salt” or “electrolytes”. Labels mix these up all the time. Table salt is about 39% sodium by weight, so 1 g of salt carries roughly 390 mg of sodium.

Each format has a trade-off:

• Sports drinks tie sodium to fluid. Easy, but if you need to drink less (cool night section) you also get less sodium, and if you drink more you get more.
• Caplets and tablets separate sodium from fluid, so you can drink plain water from aid stations and still hit your number. You have to remember to take them, and they need water to go down.
• Salty food such as crackers, salted potatoes or soup at night checkpoints works well in ultras, but the sodium content is hard to know.

Our Elec Stamina caplets list 220 mg of sodium each, and the pack directions pair one caplet with every 500 ml of water you drink during exercise, up to ten a day. That pairing keeps the sodium tied to your fluid instead of to a clock, which matters for the reasons above. If your runs are under about two hours, you don’t need them.

A worked example: a five-hour Penang Bridge Marathon

Say a runner measured a sweat rate of 1.3 litres an hour on a hot Sunday long run around Bukit Kiara, and plans a five-hour marathon. They expect to drink around 0.7 litres an hour from the water stations, a bit more than half their loss.

Without a sweat test they don’t know their sweat sodium, so take 40 mmol per litre (about 920 mg) as an illustration. Their theoretical loss is about 1,200 mg an hour, or 6,000 mg over the race. Because they replace only about half their fluid, McCubbin’s model suggests they need far less than half that sodium back. Taking 200 to 350 mg an hour from a sports drink, salty snack or caplets gives them a sensible margin without chasing the full loss.

Now change one thing. The same runner drinks 1.2 litres an hour because a forum told them to “stay ahead of dehydration”. Now they’re replacing over 90% of fluid losses, and the sodium they take in matters a lot more. The better fix is usually to drink less, not to swallow more salt.

For the fluid side of that sum, read Running in Malaysian Heat: How Should You Hydrate? For the carbohydrate side, see How Many Carbs Per Hour Do You Need for Running?, and for a hilly, wet-season example, our Bentong Marathon fuel plan.

What are the warning signs you’ve got it wrong?

The most useful warning sign is your weight. If you finish a long run or race heavier than you started, you drank too much, whatever was in the bottle. The 2015 international consensus on exercise-associated hyponatraemia lists lightheadedness, nausea and weight gain during an event among the early signs, and names overdrinking as the main cause (Hew-Butler et al., 2015).

Cramps are a poor guide. Runners often blame sodium, but the evidence on cramp causes is mixed, and fatigue and pacing play a big part. We covered that in Leg Cramps on Long Runs.

White salt marks on your cap after a run tell you something, but they are a hint, not a measurement. If you race ultras and see them every weekend, a proper sweat sodium test is money well spent.

References

1. Barnes KA, Anderson ML, Stofan JR, et al. (2019). Normative data for sweating rate, sweat sodium concentration, and sweat sodium loss in athletes. Journal of Sports Sciences, 37(20), 2356-2366. doi:10.1080/02640414.2019.1633159
2. McCubbin AJ (2022). Modelling sodium requirements of athletes across a variety of exercise scenarios. European Journal of Sport Science, 23(6), 992-1000. doi:10.1080/17461391.2022.2083526
3. Sawka MN, Burke LM, Eichner ER, et al. (2007). American College of Sports Medicine position stand: exercise and fluid replacement. Medicine & Science in Sports & Exercise, 39(2), 377-390. doi:10.1249/mss.0b013e31802ca597
4. Hoffman MD, Stuempfle KJ (2015). Sodium supplementation and exercise-associated hyponatremia during prolonged exercise. Medicine & Science in Sports & Exercise, 47(9), 1781-1787. doi:10.1249/MSS.0000000000000599
5. Hoffman MD, Hew-Butler T, Stuempfle KJ (2013). Exercise-associated hyponatremia and hydration status in 161-km ultramarathoners. Medicine & Science in Sports & Exercise, 45(4), 784-791. doi:10.1249/MSS.0b013e31827985a8
6. Sims ST, van Vliet L, Cotter JD, Rehrer NJ (2007). Sodium loading aids fluid balance and reduces physiological strain of trained men exercising in the heat. Medicine & Science in Sports & Exercise, 39(1), 123-130. doi:10.1249/01.mss.0000241639.97972.4a
7. McCubbin AJ, Allanson BA, Caldwell Odgers JN, et al. (2020). Sports Dietitians Australia position statement: nutrition for exercise in hot environments. International Journal of Sport Nutrition and Exercise Metabolism, 30(1), 83-98. doi:10.1123/ijsnem.2019-0300
8. Hew-Butler T, Rosner MH, Fowkes-Godek S, et al. (2015). Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference. British Journal of Sports Medicine, 49(22), 1432-1446. doi:10.1136/bjsports-2015-095004