Learn · Fueling
Sodium and sweat: how much salt do you lose on a long ride?
The short answer: you lose sodium with every litre of sweat, and how much varies hugely from rider to rider. A sensible plan replaces some of it through what you drink, without ever drinking more than you sweat to get it in.
How much sodium is in sweat?
A lot, and very differently for different people. In athletes, whole-body sweat typically holds about 10 to 70 millimoles of sodium per litre, which is roughly 230 to 1600 milligrams per litre 1. Measurements from small skin patches read somewhat higher. The same review found large differences within the same athlete from day to day, and that measuring sweat sodium well is harder than it looks 1.
Multiply by sweat rate and the totals add up fast. At a litre and a half of sweat an hour and 900 mg of sodium per litre, a five-hour ride costs several grams of sodium.
Sodium does not make overdrinking safe
Exercise-associated hyponatremia, a dangerous drop in blood sodium, is mainly caused by drinking more than you lose, sustained over a long event 2. Adding sodium to your drinks is not a licence to drink more. Keep drinking below your sweat losses first.
Drinks that contain electrolytes as well as carbohydrate can have benefits over water alone in some circumstances 3.
Are you a salty sweater?
The only reliable answer is a sweat test. A common rule of thumb, not from a study, is that white salt marks on your kit or stinging eyes after a hot ride point to salty sweat.
How the FondoLab planner handles it
The planner asks how salty your sweat is and plans 500, 800 or 1100 mg of sodium per litre you drink. These are FondoLab defaults inside the range found in athletes, not measured values for you. Tying sodium to the fluid you drink means the plan never asks you to drink more to get more salt in. Legs above 1000 mg an hour get a note to spread the intake out.
References
- Baker LB (2017). Sweating rate and sweat sodium concentration in athletes: a review of methodology and intra/interindividual variability. Sports Medicine 47(Suppl 1):111–128. doi:10.1007/s40279-017-0691-5
- Hew-Butler T, Rosner MH, Fowkes-Godek S, et al. (2015). Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. Clinical Journal of Sport Medicine 25(4):303–320. doi:10.1097/JSM.0000000000000221
- Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS (2007). American College of Sports Medicine position stand. Exercise and fluid replacement. Medicine and Science in Sports and Exercise 39(2):377–390. doi:10.1249/mss.0b013e31802ca597