Hydration and Electrolytes for Runners
Staying adequately hydrated helps you run well, and the mistake most runners actually make is the obvious one — not drinking enough, especially in heat and on long efforts. The goal is simply to replace roughly what you sweat: enough to stay on top of your losses, without going to the rare opposite extreme of drinking far too much. This is general education, not medical advice.
What you lose when you sweat
Sweat is mostly water plus electrolytes — chiefly sodium. How much you sweat, and how salty it is, varies enormously between runners and with heat, humidity, and intensity, so there's no single number of bottles that's "right" for everyone1. The aim is to match your own losses reasonably well.
Dehydration is the common problem
For the large majority of runners, the real-world risk is *under*-drinking. Losing a meaningful fraction of your body weight in sweat without replacing it raises your heart rate and core temperature, makes a given pace feel harder, and degrades performance — and in the heat, significant dehydration contributes to heat illness1. This is what most runners should focus on: on longer or hot runs, plan to drink, and don't finish a hard session having taken on nothing.
How much to drink
For most runners in most conditions, drinking to thirst is a sound, practical guide1. But thirst can lag behind your losses when it's hot or the effort is long, so in those conditions drink proactively rather than waiting until you're parched — carry fluid, and use aid stations. The longer and hotter the run, the more deliberate about drinking you should be.
When electrolytes matter
For longer or hotter efforts, and for "salty sweaters," replacing sodium — via a sports drink, electrolyte tablets, or salt with food — helps you hold onto fluid and feel better, and the sodium helps maintain the thirst drive that keeps your intake on track. For a short, easy run in mild conditions, plain water is fine.
Know your own sweat rate
The best way to dial this in is to learn your own numbers. Weigh yourself before and after a run: a drop of about 1 kg (2 lb) is roughly 1 liter of sweat lost. That tells you, in your conditions, how much you actually need to replace — far more useful than any generic guideline. Day to day, pale-straw-colored urine is a reasonable check that you're in range.
Can you drink too much? Yes — but it's the rarer mistake
At the opposite extreme from dehydration, drinking *far more* than you sweat dilutes the sodium in your blood and causes exercise-associated hyponatremia — which is less common than dehydration but can be serious, ranging from nausea and headache to confusion and, rarely, seizures1. It shows up most in slower runners in long events who drink at every opportunity well beyond thirst. The takeaway isn't to drink timidly — it's that the target is *replacing your losses*, not pouring in as much fluid as possible. Match your sweat; don't force far past it.
Safety
This article is general education, not medical advice. Both extremes can be dangerous: seek prompt care for signs of serious heat illness or severe dehydration (dizziness, confusion, faintness, or stopping sweating in the heat), and for signs of exercise-associated hyponatremia (nausea, headache, or confusion, especially with bloating after drinking a large amount of fluid). When something is clearly wrong during or after a hard or hot effort, stop and get help.
Sources
- McDermott BP, Anderson SA, Armstrong LE, Casa DJ, Cheuvront SN, Cooper L, Kenney WL, O'Connor FG, Roberts WO. National Athletic Trainers' Association Position Statement: Fluid Replacement for the Physically Active. Journal of Athletic Training 52(9):877-895 (2017). (NATA position statement on fluid replacement, dehydration, and hyponatremia risk) ↩
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