Salt, Sweat, and Smart Hydration
Br Dr Andrew Crockett
I have spent a lot of time helping ambitious people do hard things in hot, messy, real world conditions. We either drink too little and run hot, or drink too much and dilute ourselves. The good news is that a few composition tweaks to what’s in your bottle, and when you drink it, make a measurable difference to both performance and safety.
In an area clouded by brand messaging and ambiguity, I’ve cleared up the uncertainty with an evidence based playbook for busy humans who like data, dislike dogma, and want their hydration strategy to hold up in the lab and on the trail.
The Hydration Paradox
Dehydration can wreck performance. Once body mass loss hits about 2%, many individuals experience meaningful drops in their body’s ability to circulate blood effectively and control their core temperature. This often leads to a drop in performance, especially in the heat. For long, hot days, moving to planned fluid intake becomes a vital strategy [10,15,17].
Overdrinking is Dangerous. The primary cause of Exercise-Associated Hyponatraemia (EAH) is simply taking in too much fluid relative to sweat losses. While sodium replacement is important, it will not save you if you out-drink your sweat. The core guardrail remains: avoid finishing an effort heavier than you started [11,19,21].
Sodium, Not Slogans, Drives Hydration. The term "electrolyte" is misleading. Many drinks labelled as such contain only trivial sodium, yet sodium is the one mineral that truly controls plasma volume and osmolality during heat stress. Typical sports drinks carry 10-25 mmol/L of sodium; this is often critically too low when sweat losses and fluid intake are high [10,12,16].
What the Current Evidence Says
If you're drinking a lot, you also need real salt. When you're sweating heavily and trying to replace that fluid, typical sports drinks don't have enough sodium. Solutions with three times the salt (around 60 mmol/L) keep your blood volume stable and help your body manage the heat better than lower-salt options. This is crucial for sustained effort [1].
Keep your drink low sugar for fast hydration. To get fluid into your bloodstream as quickly as possible, your drink needs a low concentration of particles. That means avoiding highly concentrated sugary mixes. If your main goal is hydration, a modest, light mix gets the job done fastest [17,18].
Use recovery drinks (ORS style) to stop peeing. After an intense effort, your body wants to shed excess fluid via urine. Specialised recovery drinks (like Oral Rehydration Solutions) are designed with a higher salt content that signals your kidneys to keep the fluid you just drank. This speeds up rehydration significantly. Target replacing 100-150% of your lost body mass [2,3,10,12,17,19].
A sodium 'pre-load' can be a strategic advantage. Taking a calculated amount of salt and water before a long effort helps increase your total body water from the start. This expansion helps your heart and cooling system work more efficiently, often resulting in lower strain and better performance, though you must always test for stomach tolerance [4,5,9].
Salt pills won't fix poor drinking habits. For ultra-endurance athletes, taking personalised salt capsules only helps if you're replacing a large amount of your sweat losses. If you're drinking modestly, salt capsules don't magically change your fluid balance or overall drinking behaviour [7,19].
Cramps are a training issue, not a salt issue. While severe salt and fluid loss can contribute to cramping, the primary cause is typically neuromuscular fatigue, your muscles being overworked. Don't rely on salt pills as a universal anti-cramp cure. Focus on training your muscles and using salt strategies to maintain blood volume [8,11,13].
A Simple Playbook
Think of hydration like a team sport: roles (sodium, carbohydrate, water) and timing matter.
Before Heat Exposure (60-120 minutes prior)
The goal is to start fully loaded (euhydrated).
Arrive euhydrated (pale straw urine, stable morning body mass) [10].
If access to fluid will be limited or heat load is high, consider a sodium preload: 500-700 mL of a drink containing roughly 20-60 mmol/L sodium.
Practical Reference: This is the equivalent of adding about 0.5 to 1.5 grams of salt (table salt/NaCl) per litre of fluid. Keep the solution light (hypotonic).
Trial for GI tolerance [5,9,16].
During Prolonged Effort (>90mins)
The strategy depends on the risk level (heat vs. performance).
Strategy:
In hot, high-sweat conditions, planned drinking is critical to prevent dangerous thermal strain.
In normal or cool climates, planned drinking is primarily for maximising performance when the duration exceeds 90 minutes or intensity is very high.
Aim to keep body-mass loss within 1-2% for most sports [10,15,17].
Composition Targets (When drinking substantially):
Sodium: 45-60 mmol/L (about 1.0-1.4 g sodium per litre). For reference: this is 3 to 6 times the sodium found in most conventional sports drinks. [1,2,3,18].
Potassium: Optional 5-10 mmol/L [18].
Carbohydrate: 2-4% (20-40 g/L) if hydration is the priority; higher (up to 8%) if fuelling is paramount [10,12,16].
Keep it hypotonic (light/low concentration) for faster gastric emptying and intestinal water uptake [17,18].
Guardrails:
Never exceed your likely sweat rate; avoid weight gain [11,21].
In ultra-endurance, drink to thirst, and accept larger body-mass losses to avoid hyperhydration [21].
After (First 2-3 hours)
The objective is rapid fluid retention to stabilize systems quickly.
Volume: Replace 1.25-1.5 L per kg of body mass lost, especially if you need to be ready again the same day [10,12,19].
Composition: Use a higher-sodium, lower-osmolality drink (ORS profile) to reduce urine output.
A modest dose of potassium (e.g., 20 mmol/L within an ORS) is appropriate.
Add a salty meal alongside [2,3,17,19].
DIY Hydration Mixes (Per Litre)
NB. Sodium citrate can be gentler on the stomach. Many commercial electrolyte tablets can under dose sodium; check the label for mmol/L or mg sodium per litre, not just “electrolytes” [10,16].
Daily Use? The Baseline Rule
The evidence is clear: most hydration needs are met through water and whole foods. For the majority of your day-to-day life and even for many short workouts, commercial electrolyte drinks are an unnecessary supplement.
When Water and Food Are Adequate: If you eat a balanced diet that includes salt, fruits, and vegetables, plain water is the only liquid necessary. For routine exercise under 90 minutes (all climates) and short post-sauna sessions, water, combined with normal nutrition, is sufficient. Prioritising high-water foods (like cucumbers and melons) and having salt with meals is the foundational, effective hydration strategy.
When Supplementation Becomes Necessary (The Threshold): High-sodium/high-electrolyte drinks are only physiologically necessary when the rate of fluid and salt loss is too high to be safely replaced by just water and a single meal. This typically involves scenarios where both large volume and performance are at risk (e.g., prolonged endurance, intense heat exposure, rapid rehydration, or extreme/extended sauna/hot yoga sessions).
Caveats: Consider targeted sodium on consecutive heavy-sweat days, in very low-carb/ketogenic phases (which increase sodium excretion), or if you use diuretics. Medically supervised ORS can be appropriate during gastrointestinal losses, whereas potassium-containing products require caution in chronic kidney disease or with ACE inhibitors/ARBs [10,11,16,18,21]. Note that heat acclimation typically lowers sweat sodium over 1-2 weeks, so needs often fall with adaptation.
The Critical Role of Acclimation
Any advanced hydration strategy operates on the assumption that the body has successfully adapted to the heat stress it is facing. This adaptation is called heat acclimation (HA).
The military often mandates heat acclimation periods for personnel moving to hot climates. For instance, in many field deployments, soldiers are advised to carry and drink plain water, often with salty rations or an ORS/higher-sodium drink reserved for rapid rehydration or severe symptoms. This strategy works because personnel who have completed HA are physiologically altered in ways that minimise the burden of heat stress:
Lower Sweat Sodium Concentration: HA causes sweat glands to become much more efficient at retaining sodium, meaning less is lost in the sweat (sometimes decreasing by up to 50%). This reduces the need for constant, high-sodium drinks during continuous activity.
Increased Plasma Volume: HA increases blood volume, which stabilises cardiovascular function and makes the body more resistant to the central strain of dehydration.
For athletes moving from cold training zones to hot (e.g., skiing to cycling, or northern winter to a race in the desert), failing to acclimate is a critical failure point. Even if your hydration strategy is compositionally perfect, moving rapidly between extreme thermal environments without 7-14 days of progressive heat exposure will lead to drastically higher core temperatures, elevated heart rate, and an earlier onset of performance decline, simply because the body's cooling mechanisms are inefficient. Hydration and electrolytes are essential, but they cannot replace the physiological overhaul provided by proper acclimation.
What About Potassium, Magnesium, and Friends?
Your body is a finely tuned machine, and sodium does the heavy lifting for hydration by regulating extracellular fluid volume. Potassium, chloride, magnesium, and calcium are essential but play distinct supporting roles that don't always require acute dosing in your bottle.
Potassium (K): This is the main intracellular cation. In hydration, it complements sodium, especially in rapid recovery ORS formulations (around 20 mmol/L K) [2,17]. Safety check: Avoid supplemental K if you have kidney disease or take certain medications (like ACE inhibitors/ARBs) [10,11,16].
Chloride (Cl-): Pairs with sodium to maintain extracellular osmolality. When you use common salt (NaCl) or an ORS, chloride is usually provided adequately [18].
Magnesium (Mg): A vital cofactor in energy metabolism. Acute magnesium in beverages has little evidence for preventing exercise-associated muscle cramps in the heat [10,11,13]. High doses commonly cause diarrhoea [9,10].
Calcium (Ca): Sweat losses are minimal, and there’s no good evidence that adding calcium to sports drinks improves acute hydration or performance [10,18].
Bottom line: For performance hydration, get sodium and osmolality right first. Add modest potassium (especially in recovery) and don’t chase magnesium or calcium in the bottle unless there’s a specific deficiency or medical indication [12,17,18].
Checklist
The Bottom Line
Don’t overthink electrolytes. For daily life and low-demand exercise, water and whole foods are the most evidence-based strategy. When you push performance and must replace large volumes of sweat, the rules change: put enough salt in the solution (45-60 mmol/L) and keep it light (hypotonic). That mindset has served me well from mountains to boardrooms to hot training grounds.
References
Wijering L, et al. A randomized, cross-over trial assessing effects of beverage sodium concentration on plasma sodium concentration and plasma volume during prolonged exercise in the heat. European Journal of Applied Physiology 2022.
Fan PWH, et al. Post-exercise rehydration with oral rehydration solution compared with sports drink or water after exercise-induced dehydration. Journal of the International Society of Sports Nutrition 2020.
Ly NQ, et al. Post-Exercise Rehydration in Athletes: Effects of Sodium and Carbohydrate in Commercial Hydration Beverages. Nutrients 2023.
Convit L, et al. Sodium Hyperhydration Improves Cycling Time-Trial Performance Without Increasing Physiological Strain in Unacclimatized Female Athletes. Medicine and Science in Sports and Exercise 2024.
Gigou P-Y, et al. Pre-Exercise Hyperhydration-Induced Bodyweight Gain Does Not Alter Prolonged Treadmill Running Time-Trial Performance in Warm Ambient Conditions. Nutrients 2012.
McCubbin AJ, et al. Personalized sodium replacement during ultra-endurance running in the heat: a double-blind, randomized, crossover trial. Scandinavian Journal of Medicine & Science in Sports 2023.
Lau WY, et al. Oral Rehydration Solution Reduces Muscle Cramp Susceptibility After Exercise-Induced Dehydration. Clinical Journal of Sport Medicine 2020.
Jardine WT, et al. The Effect of Pre-Exercise Hyperhydration on Exercise Performance, Physiological Outcomes and Gastrointestinal Symptoms: A Systematic Review. Sports Medicine (Auckland, N.z.) 2023.
McCubbin AJ, et al. Sports Dietitians Australia Position Statement: Hydration for Exercise and Sport. International Journal of Sport Nutrition and Exercise Metabolism 2020.
Sawka MN, et al. Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. British Journal of Sports Medicine 2015.
Horswill CA. Effective Hydration Strategies for the Sports Dietitian. Sports Nutrition & Performance Enhancement 2018.
Lindinger MI, et al. Exercise-Associated Muscle Cramps: an Update. Sports Medicine (Auckland, N.z.) 2024.
Rosner MH, et al. Exercise-Associated Hyponatremia. Clinical Journal of Sport Medicine 2021.
Kenefick RW. Drinking Strategies: Planned Drinking Versus Drinking to Thirst. Sports Medicine (Auckland, N.z.) 2018.
Sawka MN, et al. American College of Sports Medicine position stand. Exercise and fluid replacement. Medicine and Science in Sports and Exercise 2007.
Yun H-J, et al. The effects of fluid absorption and plasma volume changes in athletes following consumption of various beverages. BMC Sports Science, Medicine and Rehabilitation 2022.
Baker LB, et al. Optimal composition of fluid-replacement beverages. Comprehensive Physiology 2014.
Maughan RJ, et al. Optimizing the restoration and maintenance of fluid balance after exercise-induced dehydration. Journal of applied physiology 2017.
Rowlands DS, et al. Hypotonic Beverage Consumption and Endurance Running Performance: A Systematic Review and Meta-analysis. International Journal of Sports Nutrition and Exercise Metabolism 2021.
Hoffman MD, et al. Considerations for ultra-endurance activities: part 2 - hydration. Research in Sports Medicine 2018.
