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Sodium might be the most over-thought nutrient in endurance sports. You may have been told that water alone will not hydrate you. Most of that is marketing dressed up as physiology.
So we sat down with Dr Alan McCubbin across three episodes of Fuelin Sessions to work through his 2025 review paper on sodium intake for athletes. It is the most complete attempt yet to turn vague guidelines into actual numbers. Here is the whole thing, before, during and after exercise, in plain language.
The one idea to hold onto before we start: sodium and water are married. Sodium only matters in relation to how much fluid you are losing and replacing. Almost every sodium problem athletes run into, gut issues, hyponatremia, the lot, comes from a mismatch between the two. Plan sodium on its own and you will get it wrong.
Day to day: you are almost certainly getting enough
The most common belief is that athletes need more sodium every day than regular people. The data says otherwise.
Most adults eat well above the public health target of under 2400 mg a day. Endurance athletes measured over multiple days came in around 3200 to 3900 mg a day on average, with some pushing past 6000 mg. The reason is simple: sodium intake rises with food intake, and athletes eat more food. As your training volume climbs, your sodium climbs with it, without you doing anything deliberate.
Your kidneys and sweat glands also adjust losses to match intake, settling sodium balance over roughly a week. So the trendy habit of dumping electrolytes in your water bottle every day, training or not, is solving a problem you do not have.
The "water doesn't hydrate you" line is a misreading. If you skull a huge bolus of plain water on an empty stomach then yes, a chunk of it runs straight through you. But eat any food alongside it and that effect disappears. If you are not significantly dehydrated, you do not need sodium to hold onto fluid. You may just need to stop chugging litres of water between meals out of habit.
Before exercise: useful in two specific cases
Pre-loading sodium is worth doing in two situations, and pointless in most others.
Case one: you turn up dehydrated. Some athletes habitually start sessions under-hydrated, usually because drinking is not front of mind in the chaos before training or a race. Adding sodium in the hours beforehand can potentially nudge thirst and pull your fluid intake up toward where it needs to be.
Case two: you are hyperhydrating before a hot, hard effort. When fluid losses are going to be brutal and you cannot drink enough during the event to keep up, topping up total body water beforehand can help. The research protocol is roughly 20 to 25 mL/kg of fluid in the 1 to 4 hours before, with enough sodium to actually hold it. This can be adjusted to lower volumes for athletes struggling with that amount of fluid yet note that the sodium amount would also need to be adjusted to avoid GI issues.
The numbers that matter:
- Using capsules, around 275 to 420 mg of sodium per 100 mL of fluid maximises retention. This amount would be tough to swallow in fluid as it would be extremely salty!
- If you want it in the drink itself, drop to around 100 to 125 mg per 100 mL, because anything saltier than that tastes foul to most people and you simply will not drink it.
NOTE: There are exceptions to these rules with products using sodium citrate such as Precision Hydration 1500 tablets.
- If you push sodium concentration too high in solution and you also risk pulling fluid into your gut, which means GI distress.
Two myths to kill here. First, multi-day "salt loading" is a waste of time. Over three days of doubling your intake you retain barely a fifth of the extra. A single acute load in the final few hours before exercise retains far more. Your kidneys clear the rest. Second, a high sweat sodium test result is not a reason to load for a week. It just is not how the body works.
One caveat for weight-category athletes cutting sodium to drop water weight: the evidence that this actually works is thin, and combining it with water loading and fluid restriction can edge you toward hyponatremia. Tread carefully.
During exercise: this is where most of the noise lives
Replacing sodium during exercise is the belief athletes hold most strongly, and it is where the marketing is loudest. Let us go through the four reasons people give, in order.
"A specific sodium concentration helps you absorb fluid and carbs." No. Controlled studies do not support tuning your drink's sodium to optimize absorption. You do not need one bottle for hydration and another for sodium. Pick the concentration you can stomach and drink.
"Sodium drives thirst so I drink more." Sometimes, but the effect is small and inconsistent, especially when you are already drinking to a plan to hit your carbs. In shorter and team sports it is mostly about whether the drink tastes good enough to keep drinking. Keep added sodium under about 100 mg per 100 mL or palatability tanks unless using products designed weith sodium citrate that can allow higher intakes. Personal taste will determine the amount of sodium tolerated.
"Salt stops cramps." This is the big one, and the honest answer is: probably not the way you think. Cramp is a messy, multi-factor problem that changes from person to person and day to day. The cases where sodium clearly mattered involved chronically salt-deficient labourers a century ago who were also severely dehydrated, a scenario that basically does not exist in modern athletes. Sodium might play a bit part by stopping a rapid drop in blood sodium, but if you are blaming cramp purely on salt loss, you are likely ignoring the actual causes (carb intake, hydration status, fatigue, pacing, training load).
"Sodium prevents hyponatremia." Now we are onto the reason that genuinely holds up, and it is more specific than you would expect. Exercise-associated hyponatremia is mostly caused by drinking too much, not by failing to eat salt. But sodium does help in one window: when you are replacing more than 70% but less than 100% of your fluid losses. That mainly happens in long, lower-intensity efforts: think events over four hours where your sweat rate is moderate (under about 1800 mL/h) and you can realistically drink that much.
Here is the part that reframes everything. In most sports, you cannot or do not need to replace 70% of your fluid losses. When that is true, your blood sodium actually rises during exercise even if you take in zero sodium. Trying to "replace 100% of sweat sodium losses" in that situation does not help. It can push you toward the high end of normal or beyond.
Picture a 95 kg rugby player sweating 2.5 litres an hour who only manages to drink 500 mL across a match. He finishes down 3% body mass and has lost a stack of sodium. With no sodium intake at all, his blood sodium lands at the top of the normal range. Try to fully replace what he lost and you tip him into mild hypernatremia. More salt was the wrong answer.
So the practical rule for during exercise: season to taste, and consider sweat testing and targeted sodium replacement if you are doing endurance training & racing (i.e races lasting more than 4 hours) where you will replace a high proportion of your fluid losses over many hours. For everything shorter or more intense, a sweat sodium test will likely not change what you should do.
And on performance: at this point in time, there is limited evidence that sodium makes you faster on its own. It can help you drink better. Sodium is a support act to fluid balance, never the headliner. If you get it right and your sodium, and fluid intake prevent GI issues and carmping, then it is possible to consider it performance enhancing.
After exercise: your kidneys have already handled it
Post-exercise, athletes reach for salt to "replace what they lost" and to rehydrate. Two clarifications.
Rehydration: sodium does help you hold onto fluid, but mainly when you are drinking low-calorie fluids on their own. The moment you eat food or drink something like milk alongside your food, then the food itself slows things down and does the retention work for you. Adding salt on top adds little. So if rapid rehydration on fluids alone is the goal (tight turnaround, hot conditions), sodium matters. If you are eating a normal recovery meal, relax.
Replacing the deficit: you do not need to fully top up the sodium you lost. The moment you stop sweating, your kidneys clamp down and conserve sodium, cutting urinary losses by half or more. If your deficit during exercise was under roughly 2000 mg, normal eating restores balance within about 24 hours on its own. Only after very large deficits with a short turnaround to your next session is deliberate replacement worth the effort. Focus on eating your recovery meal and drinking fluids til you start to pee clear. Replacing your fluid will hve a bigger impact on recovery than loading the sodium in.
The takeaway
Strip away the marketing and it comes down to this:
1. You do not need daily sodium supplements. You are already eating plenty.
2. Pre-load sodium only to fix a dehydrated start or to hyperhydrate for a hot, hard effort. Use the acute dose, skip the multi-day loading.
3. During exercise, season to taste. Targeted sodium replacement and sweat testing will earn their place in longer endurance efforts in training and racing. Big efforts, sweat-rate driven, often need less sodium, not more. Use context to make your decisions.
4. After exercise, let your kidneys do the work. Full replacement is rarely necessary.
Sodium is not a standalone lever. It only makes sense as part of your fluid plan. Get the water right first, then ask what sodium that water needs. Do it the other way around and you are just guessing with expensive salt.
Thank you for reading,
Scott
This article draws on the three-part Fuelin Sessions series with Dr Alan McCubbin, built around his open-access review: McCubbin AJ. Sodium intake for athletes before, during and after exercise: review and recommendations. Performance Nutrition. 2025;1:11. https://doi.org/10.1186/s44410-025-00011-9
https://fuelin.com/podcasts/sodium-after-exercise---required
https://fuelin.com/podcasts/sodium-during-exercise---required
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