How Much Sodium Do You Need In A Marathon?

Key Takeaways

• Sodium needs during a marathon are highly individual and depend on sweat rate, sweat sodium concentration, weather, and pace.

• Most runners fall within 300-800 mg sodium per hour, with higher needs in heat or for salty sweaters.

• Sodium works best when paired with fluids and carbohydrates to support hydration and performance.

• You do not need to replace all losses, focus on consistent intake that matches your conditions and tolerance.

• The best sodium strategy is one that is tested in training and built into your overall fuelling plan.

 

Sodium is a key part of marathon fuelling, supporting both performance and hydration across the race. As you run, sodium is lost through sweat, and replacing some of these losses helps your body maintain fluid balance, muscle function, and overall performance,².

The key thing to know is that sodium needs are highly individual. They vary based on your sweat rate, how salty your sweat is, your pacing, and the conditions on race day (especially heat and humidity)¹⁻³.

The good news is that with a simple, well-practised plan, most runners can get this right and feel confident in their approach

 

Quick Answer: Sodium Needs For A Marathon

Most runners need 300-800 mg of sodium per hour during a marathon³⁻⁵. In hot conditions or for heavy/salty sweaters, needs may increase to 1000-1500 mg per hour³,⁴. Sodium can come from carb drink mixes, electrolyte mixes, salt capsules, gels or food⁵. You don’t need to replace 100% of your losses, just enough to support hydration and performance³.  Start within this range and adjust based on your training experience and race conditions.

 

Why Sodium Matters For Marathon Runners

Sodium is an essential electrolyte that supports fluid balance, nerve function, and muscle contraction²,⁴. During a marathon, both fluid and sodium are lost through sweat, so replacing fluids alone isn’t always enough¹,². Including sodium with fluids helps improve absorption and maintain more stable hydration, while also supporting blood volume and reducing symptoms like fatigue, cramping, and unwanted toilet stops⁵. It also helps maintain blood sodium levels, drinking large amounts of fluid without sodium can dilute these levels, increasing the risk of Hyponatremia during endurance events⁴. Overall, the goal isn’t to replace every milligram lost, but to support hydration and performance across the race.

 

How Much Sodium Do You Lose While Running?

Sodium losses depend on how much you sweat and how salty your sweat is. Most runners lose around 300-1500mg of sodium per litre of sweat, with many sitting somewhere in the middle¹⁻³.

This means even if two runners sweat the same amount, their sodium losses can be very different. For example, losing 1 litre of sweat per hour could equal anywhere from 200-1600mg of sodium per hour, depending on the individual.

 

Typical Sodium Loss Ranges

 

How Much Sodium Do You Need During a Marathon?

Sodium intake during a marathon should be seen as a flexible range, not a fixed target. Needs vary based on sweat rate, sweat sodium concentration, pace, and environmental conditions¹⁻³.

Most runners fall around 300-800 mg per hour, with 1000-1500 mg per hour sometimes needed in hot conditions or for salty sweaters¹,².

The best approach is to start within this range and refine your plan in training based on individual response.

 

Factors That Affect Sodium Loss (Sweat Rate, Weather, Pace, Body Size)

Sodium loss during running varies a lot between athletes and is mainly driven by how much you sweat and how concentrated your sweat is¹⁻³.

• Sweat rate: More sweat = higher total sodium loss¹.

• Weather: Hot and humid conditions increase sweat and sodium losses².

• Pace/intensity: Faster running increases heat production and sweat rate¹,³.

• Body size: Larger athletes often produce more heat and may sweat more overall.

Because these factors are different for everyone, sodium needs should be personalised rather than fixed.

 

How To Calculate Your Personal Sodium Needs

A simple way to estimate sodium needs is to work out your sweat rate first, then apply a sodium range.

Step 1: Estimate sweat rate

• Weigh yourself before and after a 60-minute run

• Subtract post-run weight from pre-run weight

• Add any fluid you drank

• 1 kg lost ≈ 1 litre of sweat per hour

Step 2: Estimate sodium loss

Multiply sweat rate by estimated sodium concentration:

• Light sweater: 300-500 mg/L

• Moderate: 500-1000 mg/L

• Heavy/salty sweater: 1000-1500+ mg/L

Step 3: Refine in training

Test in long runs and adjust based on hydration, gut comfort, and performance.

 

Sodium Intake Guidelines Before, During, & After A Marathon

Sodium supports hydration, performance, and recovery across the whole marathon¹,²

Before→ Include normal salty foods and fluids in the 12-24 hours before racing to support good hydration¹,².

During→ Sodium helps maintain hydration and fluid absorption. Most runners need ~300-800 mg/hour, up to ~1000-1500 mg/hour in heat or salty sweaters¹,²,⁵.

After→ Sodium with fluids supports better rehydration and recovery compared to water alone⁵.

 

Best Ways to Take Sodium During a Marathon

Sodium works best when taken in small, regular amounts alongside fluids and carbohydrates, rather than in large doses¹,².

Simple options:

• Electrolyte drink mixes – easiest way to combine sodium, fluid, and sometimes carbs in one bottle⁵

• Salt tablets / capsules – convenient for adding sodium when using gels and plain water

• Sports gels – Some gels contain electrolytes to help balance sodium with fluid intake

Key points:

• Start taking sodium early in the race

• Take small doses regularly (don’t wait for issues)

• Match sodium with fluids and carbs for better absorption⁵

 

Types Of Sodium Supplements For Runners

Different sodium options suit different runners depending on sweat rate, conditions, and how simple you want your race plan to be¹,².

Electrolyte drink mixes → Easy way to get sodium + fluids + carbs all together in one bottle.
Best for: simple hydration strategies and hot conditions.

Salt tablets / Salt capsules → Provide a precise sodium boost without changing your gel plan.
Best for: Runners relying mainly on gels, those looking to minimise what they carry, or athletes requiring higher sodium intake.

Gels + Electrolyte drink mixes→ Most gels are low in sodium, so they usually need electrolytes alongside them.
Best for: Ensuring both carbs, electrolytes and fluid are all met.

How to choose→ Choose based on race conditions, your preference for carrying fluids while running, and what you’ve practised in training. Most runners get the best results using a combination of options.

 

Electrolyte Tablets/Powders vs Electrolyte Capsules

Both are convenient ways to increase sodium during a marathon, but they suit slightly different needs.

Electrolyte tablets/ Powders→ Dissolve/mix with water to provide electrolytes with  fluids.
Best for: runners already carrying bottles, simple hydration strategies, and hot conditions.

Electrolyte capsules→ Contain sodium plus other electrolytes like potassium and magnesium.
Best for: Runners not wanting to carry fluids and using on-course water stations, or those needing to top up electrolyte levels alongside gels.

 

Hydration Powders & Sports Drinks

Hydration powders and sports drinks are one of the simplest ways to combine fluids, sodium, and carbohydrates in a single product, helping support steady energy and hydration during a marathon. They work by replacing fluid losses while also providing sodium to help improve fluid absorption and maintain hydration balance across the race¹,². Many also include carbohydrates, which can support energy availability when taken consistently throughout longer efforts.

They are also commonly available on course at marathon aid stations, making them a convenient option for runners who don’t want to carry all their fluids from the start.

 

 Which Type of Sodium Is Best For Absorption?

Most sports products use either sodium chloride (salt) or sodium citrate, and both are well absorbed and effective for hydration and performance¹,².

Sodium chloride (salt)

• Most common form

• Found in sports drinks and salt tablets

• Reliable and widely used

Sodium citrate

• Often used in electrolyte powders and capsules

• Milder taste

• May be better tolerated at higher intakes for some runners

 

Common Sodium Intake Mistakes to Avoid

A few simple mistakes can affect how well you hydrate and perform in a marathon.

Only drinking water → Water alone may not replace sodium lost in sweat, which can reduce hydration efficiency over long runs¹,².

Underestimating sweat losses → Sweat rate and sodium loss vary a lot between runners, so many athletes don’t take enough sodium in hot conditions or if they’re heavy sweaters¹⁻³.

Over drinking without electrolytes → Too much fluid without sodium can disrupt balance and, in some cases, contribute to Hyponatremia².

Blaming cramps on sodium alone→ Cramping is usually more related to fatigue and pacing than electrolytes on their own².

 

Example Marathon Sodium Intake Plan

A sodium plan should be simple, consistent, and aligned with fluids and carbs¹,².

Pre-race

• Normal fluids + salty foods or electrolyte drink

• Focus on starting well-hydrated

During race

• ~300-800 mg sodium per hour (adjust for heat/sweat rate)¹,².

• Small doses every 15-30 minutes

• Combine with gels and fluids

Example

• Gel + water + electrolyte drink each hour
  or

• Gel + water + salt capsules

 

Build Your Personal Marathon Fuelling Strategy

Sodium works best as part of a full fuelling plan that includes fluids and carbohydrates, rather than as a standalone target¹,². The aim is to match intake to your sweat rate, conditions, and gut tolerance.

Start with evidence-based ranges, then test and refine in training so race day feels familiar and simple. This may include trying electrolyte drinks, gels, and salt capsules in different combinations.

A range of options like those available through Aid Station, can help you build a strategy that suits your needs.Consistency and practice are key, your plan should be well-tested before race day.

 

Ash Miller
Dietitian and Nutritionist (Masters)
Bachelor of Physical and Health Education
Instagram: @ashthomo_nutrition

 

References

1. Baker LB, Dougherty KA, Kuklski TR, Chow M, Kenney WL. Sweat rate and sweat sodium: variability and testing. Sports Med. 2017;47 Suppl 1:79–98.

2. Baker LB, Cotter JD, Cheuvront SN, Kenefick RW. Variation in sweat sodium concentration. Exp Physiol. 2022;107(7):675–689.

3. McCubbin AJ. Modelling sodium requirements of athletes across a variety of exercise scenarios: identifying when to test and target, or season to taste. Eur J Sport Sci. 2023;23(6):992–1000.

4. McCubbin AJ. Sodium intake for athletes before, during and after exercise: review and recommendations. Perform Nutr. 2025;1:11.

5. Australian Institute of Sport. Sports Supplement Framework: Sports Drinks & Electrolyte Supplements. AIS; updated guideline.

Disclaimer:

The content in this blog is for general information only and is not a substitute for professional medical advice, diagnosis, or treatment. Always speak with your doctor or allied health team before changing your diet, exercise, or taking supplements, especially if you have a health condition or take medication. Please use this information as a guide only. Aid Station doesn't take responsibility for individual outcomes.