A frequent clinic question concerns sodium supplementation for athletes, particularly those training in the heat or over long distances. Before considering any protocol, it is essential to name the populations for whom routine sodium loading is not indicated: recreational exercisers, individuals with hypertension or sodium-sensitive conditions, and those with low to moderate sweat losses. For these groups, standard dietary sodium intake is generally sufficient, and aggressive supplementation may introduce unnecessary risks.
Mechanism
Sodium is the primary extracellular cation and plays a central role in fluid balance, nerve conduction, and muscle contraction. During prolonged exercise, especially in hot environments, sweat losses can be substantial, with sodium concentrations varying widely among individuals—from less than 20 mEq/L to over 80 mEq/L. When sweat rates are high and fluid replacement is hypotonic, the risk of exercise-associated hyponatremia (EAH) emerges, a condition where serum sodium falls below 135 mmol/L and can lead to neurological complications.
The body’s regulatory systems, including thirst and renal sodium conservation, are remarkably effective for most people. However, in ultra-endurance events or multi-hour training sessions, the combination of high sweat volume and high sweat sodium concentration can overwhelm these defenses, particularly if athletes overhydrate with plain water. This mechanism underlies the rationale for sodium supplementation in specific contexts.
Evidence Summary
The evidence on sodium supplementation for athletes is nuanced and often misinterpreted. A 2017 update on exercise-associated hyponatremia noted that plasma sodium was lower in patients on a low-sodium diet before and throughout exercise, suggesting that general population recommendations to lower salt intake may not be appropriate for endurance athletes training in the heat (PMC5334560). However, this does not imply that high-dose sodium loading is beneficial for all.
Research on sodium consumption during endurance exercise indicates that sodium intake in solid food or capsules has a minor influence on serum sodium and whole-body sodium balance. In one study of ultramarathon runners, the amount of sodium consumed during a 161 km race accounted for only 6–8% of the variance in post-race serum sodium (PMC8001428). This suggests that sodium supplementation alone is not a reliable defense against EAH and that overhydration remains the primary risk factor.
The National Athletic Trainers’ Association position statement on fluid replacement recommends that individual assessment of sweat electrolyte concentrations should occur before considering supplementation, as athletes with sweat sodium concentrations greater than 60 mEq/L and sweat rates exceeding 2.5 L/h may benefit (PMC5634236). No evidence indicates that athletes are helped by sodium supplementation beyond individual losses. For most athletes, consuming sodium-containing sports drinks that are hypotonic will not prevent EAH if they drink excessively during exercise (PMC8955583).
A separate line of research examines sodium bicarbonate as an ergogenic aid, primarily for high-intensity efforts. A systematic review found potential benefits for exercise durations of 30 seconds to 12 minutes, but evidence is lacking for very short sprints and elite athletes, and gastrointestinal side effects are common (PMC6544001). This is distinct from sodium chloride supplementation for hydration and should not be conflated.
Conservative Recommendation
In the absence of contraindications, the safest approach for the majority of athletes is to meet sodium needs through a balanced diet and to use thirst-guided hydration with electrolyte-containing fluids during prolonged exercise. For endurance athletes with documented high sweat sodium losses, individualized sodium replacement—ideally informed by sweat testing—may be considered, with doses typically ranging from 300 to 600 mg of sodium per hour, adjusted based on exercise duration, intensity, and environmental conditions.
It is critical to avoid the anecdotal practice of using sodium tablets to prevent hyponatremia, as this strategy lacks strong evidence and can cause gastrointestinal distress. Athletes should focus on preventing overhydration, limiting weight loss to less than 2% of body mass, and educating themselves on proper hydration methods (PMC8955583). Individual care should guide individual decisions, and any supplementation protocol should be tested in training before competition.
Disclaimer
This column is for informational purposes and does not constitute medical advice. Athletes with medical conditions such as hypertension, renal disease, or heart failure should consult their physician before modifying sodium intake. Those experiencing symptoms of hyponatremia—including confusion, nausea, or headache during or after exercise—should seek immediate medical attention. A healthcare professional can provide personalized guidance based on individual health status and performance goals.
FAQ
I sweat a lot during my 5K runs. Should I start taking salt tablets?
Almost certainly not. For efforts under an hour, even heavy sweaters rarely lose enough sodium to require supplementation—your normal diet covers it. Salt tablets often cause stomach upset and haven't been shown to prevent hyponatremia. Focus on drinking to thirst and eating a balanced meal afterward.
How do I know if I'm a "salty sweater" who needs extra sodium?
The only reliable way is a sweat test, which measures your sodium concentration. If you consistently notice white residue on your skin or clothes after exercise, you might have higher losses, but that's a rough clue, not a diagnosis. A sports medicine clinic can perform the test and help you determine if targeted replacement is warranted.
Can I just drink sports drinks to cover my sodium needs during a marathon?
Sports drinks help, but they won't fix the real problem if you're overdrinking. The evidence shows that even sodium-containing hypotonic drinks can't prevent hyponatremia if you consume excessive fluid. Drink to thirst, not ahead of it, and if you're racing for many hours, consider having a plan based on your individual sweat rate and sodium losses.
