Most marathon runners benefit from taking 300 to 700 mg of sodium per hour, which translates to roughly one salt tablet every 30 to 60 minutes depending on the tablet’s strength and how heavily you sweat. The right frequency for you depends on your sweat rate, the weather, and your body’s individual sodium concentration, so there’s no single schedule that works for everyone.
A Starting Point for Timing and Dosage
A practical baseline is 300 to 500 mg of sodium per hour for moderate sweaters, and 700 mg or more per hour for heavy or salty sweaters. Most commercial salt tablets contain between 100 and 250 mg of sodium per capsule, so you’d take one to three tablets per hour depending on the brand. Spacing them out every 30 to 45 minutes, rather than taking them all at once, helps your gut absorb the sodium steadily and reduces the chance of nausea or stomach cramping.
The American College of Sports Medicine recommends 500 to 700 mg of sodium per liter of fluid consumed during exercise lasting longer than an hour. If you typically drink about half a liter (16 ounces) of fluid per hour while running, that means roughly 250 to 350 mg of sodium per hour paired with that fluid. If you drink closer to a full liter per hour, you’d aim for the higher end.
Always take salt tablets with water. Taking them dry or with too little fluid can irritate your stomach. A good rule is at least 4 to 6 ounces of water per tablet.
Why Your Needs Are Different From Other Runners
Sodium losses during exercise vary enormously from person to person. Sweat rates among athletes range from about half a liter to over two liters per hour, and the sodium concentration in that sweat ranges from roughly 230 mg per liter on the low end to over 2,000 mg per liter on the high end. That means two runners side by side in the same race could lose wildly different amounts of sodium per hour.
You’re likely a heavier sodium loser if you notice white, gritty residue on your skin or clothing after long runs, if your sweat stings your eyes, or if you tend to cramp during extended efforts. These runners generally need to replace sodium more aggressively, closer to 500 to 700+ mg per hour. Lighter sweaters who don’t show those signs can often get by with 300 mg per hour or even less, especially if their sports drink already contains some sodium.
The most accurate way to know your numbers is a sweat test. Sports performance labs and some running stores offer them. The test measures both your sweat rate (how much fluid you lose per hour) and your sweat sodium concentration. You can estimate your sweat rate at home by weighing yourself before and after a one-hour run without drinking. Every gram of body mass lost equals roughly one milliliter of sweat. That gives you the volume side of the equation, though not the sodium concentration.
How Heat and Humidity Change the Equation
Hot, humid conditions increase your sweat rate, which increases sodium losses. When temperatures climb above 75°F or humidity is high, you’ll sweat more per hour and need to replace more sodium accordingly. If your baseline plan calls for one salt tablet every 45 minutes in cool weather, you might shift to every 30 minutes on a warm race day.
The tricky part is that heat also makes you drink more, and overdrinking is its own serious risk. Sodium replacement in hot weather only works if your fluid intake stays proportional. Drinking large volumes of plain water without enough sodium can dilute your blood sodium levels dangerously, a condition called exercise-associated hyponatremia.
The Overhydration Risk
Hyponatremia is one of the most serious medical emergencies at marathons, and it’s caused not by too little sodium intake but by too much water intake relative to sodium. It happens when your blood sodium drops below normal levels, and symptoms can appear during or even up to 24 hours after a race. Early signs include bloating, nausea, and a lack of thirst despite drinking plenty. Severe cases can cause confusion, seizures, and worse.
The best prevention is simple: drink to thirst, not on a rigid schedule. If you feel bloated or notice you’re not thirsty but keep drinking anyway, stop. Salt tablets will not prevent hyponatremia if you’re simultaneously overdrinking. They help maintain sodium balance when paired with appropriate fluid intake, but they can’t overcome the dilution effect of excessive water consumption.
A useful self-check: if you feel bloated and aren’t thirsty during a race, that’s a signal to stop drinking temporarily. If you feel thirsty and lightheaded, that’s more likely dehydration or heat stress, and fluids with sodium are appropriate.
How to Build Your Race-Day Plan
Don’t try salt tablets for the first time on race day. Test your strategy during long training runs at race pace. Start with a conservative dose, around 200 to 300 mg of sodium every 45 minutes alongside your normal fluid intake, and adjust based on how you feel. Signs you need more sodium include early-onset muscle cramping, excessive fatigue, or a strong craving for salty food. Signs you’re taking too much include puffiness, stomach distress, or an unpleasant salty taste that lingers.
Keep in mind that gels, chews, and sports drinks also contain sodium. A typical energy gel has 50 to 200 mg of sodium, and most sports drinks provide 300 to 500 mg per liter. If you’re using those alongside salt tablets, count all sources together when estimating your hourly intake. Many runners find they don’t need standalone salt tablets at all if their gel and drink combination already covers their sodium needs.
For a four-hour marathoner who sweats moderately in mild weather, a reasonable plan might look like one salt tablet (200 mg sodium) every 45 minutes, plus a gel with 100 mg sodium every 45 minutes, plus sips of sports drink at aid stations. That puts total sodium intake somewhere around 400 to 500 mg per hour, well within the recommended range. A heavier sweater racing in heat might double the salt tablet frequency or switch to a higher-sodium product.
Track what works across several long runs before committing to a race-day protocol. Your gut tolerance, sweat rate, and perceived energy levels during those runs are better guides than any formula.