How much salt to drink before a marathon?

December 21, 2025 •

4 min read

Up to 13% of marathon runners can experience hyponatremia, a dangerous condition resulting from low blood sodium, often caused by over-drinking plain water. Knowing precisely how much salt to drink before a marathon is essential for balancing electrolytes and ensuring a strong, safe race.

Quick Summary

This guide details the importance of pre-race sodium intake for marathon runners. It covers understanding individual sweat loss, implementing a strategic salt intake plan, and balancing fluid consumption to prevent performance-impairing and dangerous electrolyte imbalances.

Key Points

Preload with High Sodium: Drink a strong electrolyte solution (approx. 500ml of >1000mg/L sodium) the night before and again 90 minutes before the race.
Practice in Training: Never test a new hydration strategy on race day; practice your fluid and sodium plan during long training runs to ensure tolerance.
Prevent Hyponatremia: Strategic salt intake, rather than just plain water, is necessary to prevent dangerous low blood sodium levels, especially for slower runners and those in hot conditions.
Know Your Sweat Rate: Estimate your individual fluid needs by weighing yourself before and after training runs, and note if you are a 'salty sweater' (visible salt residue).
Choose Your Method: Replenish sodium with appropriate sports drinks, electrolyte capsules, or chews, which allow for precise dosing and effective absorption.
Listen to Your Body: While general guidelines exist, your hydration strategy must be personalized. Pay attention to your body's signals and adjust based on conditions and your unique sweat loss.

Why Pre-Race Salt Intake is Critical for Marathon Runners

For marathon runners, proper hydration is more complex than simply drinking lots of water. When you run long distances, your body loses significant amounts of sodium through sweat, which is a critical electrolyte for maintaining fluid balance, nerve function, and muscle contractions. If you consume large volumes of plain water to compensate for fluid loss without adequate sodium replacement, you risk diluting the sodium concentration in your blood, leading to a condition called exercise-associated hyponatremia (EAH).

Symptoms of EAH can range from mild issues like headaches and confusion to severe, life-threatening complications such as seizures and coma. For this reason, a strategic approach to sodium intake both before and during a marathon is vital for every runner.

Understanding Your Unique Sodium Needs

There is no one-size-fits-all answer for how much salt to drink before a marathon, as individual needs vary dramatically. Factors like genetics, fitness level, acclimation to heat, and the intensity and duration of your race all play a role in how much sodium you lose. Runners often fall into one of three general categories when it comes to sweat sodium concentration:

Low-salt sweaters: Lose less sodium per litre of sweat.
Typical sweaters: The average athlete falls into this category.
Salty sweaters: Lose a high concentration of sodium, often leaving white salt streaks on their skin or clothing after a run.

To determine your personalized needs, testing is recommended. While lab sweat testing provides the most accurate data, a simple field test during training can give you a good estimate. Weigh yourself naked before and after a one-hour run in race-like conditions, and subtract any fluid consumed. A significant weight loss indicates a high sweat rate. Observing white residue on your gear is a key sign you lose a high amount of sodium.

Preloading: The Strategic Salt Intake Before Your Marathon

Instead of "salt loading" with excessive intake, a scientifically supported strategy is "sodium preloading". This involves consuming a strong electrolyte drink before your race to boost blood plasma volume, giving your cardiovascular system a better buffer for the demands of the marathon, especially in hot conditions.

A Typical Preloading Schedule

Evening Before the Race: Drink 500ml (16oz) of a higher-strength electrolyte solution, ideally one containing over 1000mg of sodium per litre. This helps to expand your blood plasma volume and ensure you start with optimized fluid reserves.
Morning of the Race (approx. 90 minutes before): Consume another 500ml (16oz) of the same strong electrolyte drink. It's crucial to finish this at least 45 minutes before the start to allow your body to absorb the electrolytes and excrete any excess, minimizing the need for last-minute porta-potty stops.

Sodium Intake Options: A Comparison

Runners can replace sodium through various products and foods. Choosing the right method depends on your personal preference and race-day logistics.


Method	Pros	Cons	Typical Sodium per Serving	Best For
Electrolyte Drink Mixes	Easy to digest; combines fluid, carbs, and electrolytes; various flavors available.	Can be bulky to carry; some are too dilute for effective preloading.	200–500mg per 12-16 oz.	During the race, and for general daily hydration leading up to the event.
Salt Pills/Capsules	Highly concentrated; allows for precise and easy dosing; small and portable.	Must be taken with water; risk of stomach upset if not taken correctly; no carb content.	100–350mg per capsule.	Heavy salt sweaters or those with specific sodium targets; use in combination with a carb source.
Salt Sticks/Chews	Convenient and portable; offers quick absorption through chewing; good for constant, small top-ups.	Flavor can be an issue; can be less precise than capsules.	50–100mg per chew.	Steady replacement of smaller electrolyte amounts during the race.
Homemade Solution	Cost-effective; customizable; allows for specific ingredient control.	May not be as palatable; requires pre-race preparation; difficult to carry large quantities.	Varies based on recipe.	Training runs and for those who prefer natural ingredients.
Salty Foods	Easy to eat during long events; provides carbs and other nutrients; familiar taste.	Can be heavy on the stomach; less precise dosing; may not be available on course.	Varies widely (e.g., salted pretzels).	During ultra-marathons or slower-paced events where solid food is tolerated.

The Role of Training and Practice

Race day is not the time to experiment with your hydration strategy. Every runner should practice their specific fluid and sodium intake plan during long training runs to test tolerance, absorption, and overall effect on performance. This allows you to fine-tune your fluid volume and sodium concentration based on your personal comfort and needs, especially in the weeks leading up to the event. Keeping track of your weight, urine colour, and how you feel can provide valuable data for adjusting your plan. A successful hydration plan is a well-rehearsed plan.

Conclusion

Understanding how much salt to drink before a marathon is a critical element of race preparation that can significantly impact your performance and safety. By incorporating a smart sodium preloading strategy, informed by an awareness of your individual sweat rate and sodium loss, you can ensure optimal hydration and electrolyte balance. The key is to test and refine your personal plan during training, rather than waiting for race day. By strategically replacing both fluid and sodium, you can reduce the risk of hyponatremia and set yourself up for a stronger, more successful marathon finish. For deeper insights into electrolyte balance, consider consulting a sports dietitian or exploring authoritative sources like the Gatorade Sports Science Institute..

Frequently Asked Questions

A common recommendation is to consume around 500-1000mg of sodium through an electrolyte drink 60-90 minutes before the race begins. You should also consume a similar high-sodium drink the evening before to preload your system.

Hyponatremia is a condition where blood sodium levels drop dangerously low due to excessive consumption of plain water without adequate salt replacement. It is a risk for marathon runners, especially those running for extended periods or in high heat, and can cause headaches, confusion, and in severe cases, seizures.

You are likely a 'salty sweater' if you notice a gritty feeling on your skin or see visible white salt streaks on your running gear after a workout. These are signs that you lose a high concentration of sodium and may need more replenishment.

While a salty pre-race meal (consumed 2-3 hours prior) can help offset some sodium loss, it is often not enough for effective preloading. For optimal results, use a targeted electrolyte drink in addition to your meal.

No, simply drinking large volumes of plain water before a marathon is not a good strategy and can increase your risk of hyponatremia. It is better to use a balanced electrolyte drink for preloading and to drink to thirst during the race.

During the race, good sources of sodium include sports drinks, electrolyte tablets or chews, salt pills, and some energy gels. A sports dietitian can help you find the best option for your individual needs.

If you experience symptoms of hyponatremia like nausea, confusion, or dizziness, you should stop running immediately and seek medical attention. Medical staff at a marathon are trained to treat this condition.