Electrolytes for Runners: How Much Sodium You Need, Including Hot-Weather Runs

What you actually lose when you sweat

Sweat is mostly water, plus sodium and chloride, the two halves of table salt. You also lose potassium, magnesium and calcium, but in far smaller amounts. That is why sodium is the number to watch when you read an electrolyte label.

How much you lose is personal. A 2017 review of sweat testing in athletes found that both sweat rate and sweat sodium vary a lot between people and from day to day, depending on intensity, heat, heat acclimation, fitness, body size, sex and diet. Two runners on the same route can finish with completely different needs. If your hat or shirt dries with white streaks, your eyes sting from sweat, or your skin feels gritty after a run, you are probably on the salty end.

When runners need electrolytes, and when water is enough

The ACSM position stand on fluid replacement says drinks with electrolytes and carbohydrate can beat plain water in certain situations, mainly long and hot sessions, and suggests sports drinks with about 20 to 30 mEq of sodium per liter. That is roughly 460 to 690 mg of sodium per liter, or about 14 to 20 mg per fluid ounce. Use it as a floor for long, hot runs. Heavy, salty sweaters often need more.

Find your numbers with a one-run sweat test

1. Pee, then weigh yourself in minimal clothing.
2. Run for 60 minutes at your normal training pace, in the conditions you want to plan for.
3. Track how much you drink.
4. Towel off and weigh yourself again before you drink anything else.
5. Sweat lost equals weight lost plus fluid drunk. The calculator does the math.

Here is a real-world example. A 160 lb (73 kg) runner does an hour in July heat, drinks 12 oz and loses 2 lb. That is about 44 oz (1.3 L) of sweat in an hour. Two percent of body weight for this runner is 3.2 lb, so a 2 hour long run without drinking would push well past that line. Drinking about 24 to 32 oz (0.7 to 0.95 L) an hour at the ACSM sodium range would add roughly 330 to 650 mg of sodium per hour. Repeat the test in cool weather; the numbers can drop by half.

Hot-weather running: acclimatize, start hydrated, slow down

A 2015 consensus statement on training and competing in the heat names heat acclimatization as the single most important step: repeated training sessions in the heat over 1 to 2 weeks. It also recommends starting sessions well hydrated, limiting dehydration during exercise, and using cooling where you can. Here is how that looks for runners:

• Run early. The coolest hour of a summer day is usually just before sunrise.
• Run by effort, not pace. Your normal pace at 90°F (32°C) is a much harder run. Slow down and let heart rate or breathing guide you.
• Start hydrated. The ACSM suggests about 5 to 7 mL of fluid per kg of body weight (0.08 to 0.11 oz per lb) at least 4 hours before. For a 160 lb runner, that is about 12 to 17 oz.
• Plan your water. Carry a bottle or vest, or loop past a fountain. Humidity slows sweat evaporation, so you heat up faster on muggy days.
• Cool down fast. Cold drinks, ice in a hat or a wet towel on the neck help after the run.

If you feel dizzy, confused, or stop making sense to your running partner, stop. Get to shade and get help. No workout is worth pushing through that.

The other risk: drinking too much

Dehydration gets most of the attention, but drinking far more than you sweat is a real risk too. The 2015 international consensus statement on exercise-associated hyponatremia, a dangerous drop in blood sodium, points to overdrinking as the main cause and supports using thirst to guide how much you drink. Slower marathoners are most exposed because they spend more hours passing aid stations. Sodium in your drink does not make overdrinking safe. If you finish a long run heavier than you started, drink less next time.

Where our electrolyte products fit, honestly

Our Hydration Powder (Lemonade) has 100 mg of sodium, 200 mg of potassium, 20 mg of magnesium and 40 mg of calcium per scoop, plus B vitamins and 10 calories, with no caffeine. Mixed in 14 to 20 oz of water, that comes to roughly 170 to 240 mg of sodium per liter. That is a light electrolyte drink that supports daily hydration and normal muscle function.* It works well for everyday use and shorter runs. It is not enough sodium on its own for a long, hot run if you are a salty sweater.

For those runs, add sodium from food (pretzels, salted potatoes, a salty bagel) or add a pinch of salt to your bottle: about 1/4 teaspoon of table salt carries roughly 575 mg of sodium. Our Creatine Hydration Powder (Lemon) is another option on hot days if you already take creatine: one scoop gives you 5 g of creatine with 1,000 mg of sodium, 200 mg of potassium and 60 mg of magnesium. Take one scoop a day, a few hours before your run, and never more than the label allows.

Electrolytes are one piece of the puzzle. Pair this with our marathon fueling guide for carbs, our complete guide to supplements for runners, and hydration and focus on long days. For a structured build, start the Build Endurance mission.

This article is for general education and is not medical advice. Talk to your doctor before starting a supplement, especially if you have a health condition, take medication, are pregnant or are under 18. Results vary from person to person.