Hyponatremia: how to optimize hydration and salt intake during endurance sports?

By Manuel - OVERSTIM.s

Salt, or its chemical name “sodium chloride”, is a solid compound, extracted from either rock salt or seawater.

Used mainly in cooking both as a preservative and for seasoning because of its flavour-enhancing properties, salt proves to be of paramount importance in endurance sports.

Salt and endurance

Endurance sports trigger salt loss through perspiration, and it can often be considerable (1). Someone moderately trained, who practices 1 to 2 hours of activity every 2-3 days, loses between 1.8 and 3.6 grams of sodium chloride (NaCl) during the activity. That means 700mg of sodium every hour.

Most waters naturally have an intake of less than 50 mg/L of sodium (2). Thus, we understand that water alone will not be enough to compensate for the loss of sodium during activities that last more than 2 hours. Although there is no exact value because many parameters influence it, we can agree that an average intake of 450mg of sodium per litre of water is needed to offset the losses that endurance athletes undergo.


Water contains on average 50mg of sodium per litre

An athlete’s needs are 450mg of salt per litre

What role does sodium play?

Sodium is an essential mineral for life. It regulates the distribution of water between the intracellular and extracellular environments.

Why is this so important? Because the human body is made up of 60-70% water, and these H2O molecules are in almost all the organism’s biochemical reactions. Human beings cannot survive more than 3 days without water.

Body water will always go from the most concentrated to the least concentrated sodium medium: this phenomenon is osmosis.

When an athlete works out, salt loss through perspiration is not compensated: water consumed can no longer play a role in hydration. Disturbances in the fluid balance may cause hyponatremia (blood sodium deficiency).

On the other hand, hyperhydration can also cause this phenomenon of hyponatremia. If we follow the same logic about osmosis: over-consumption of water will dilute the sodium in the body. Thus, the cells try to absorb more water to get more sodium, and oedemas will occur.

What are the consequences of a hyponatremia/sodium deficit while working out?

If the salt loss is not compensated during long workouts or from intense heat, this could lead to the appearance of hyponatremia. This blood sodium deficiency can have numerous repercussions:

–              Dehydration via biochemical and hormonal reactions is accelerated.

–              Intra/extra cellular electrolyte imbalance, appearance of oedemas.

–              Cramps, muscular difficulties.

–              Fatigue, loss of balance, vertigo, headaches, discomfort.

–              Pronounced hyponatremia can cause coma or death from the onset of oedemas at brain level.

An American study has shown that athletes who have taken on 4% weight during a race (oedemas) have a 45% risk of hyponatremia (3).

Are you worried about the risk of hyponatremia?

Hyponatremia during sports concerns endurance athletes, marathon runners and events longer than 4 hours (ultras, hikes, triathlons, ironman, etc.). This pathology does not concern strength or speed sports, where the activity is too short (4, 5, 6, 7).

Mostly concerned are:

  • Endurance competitors (longer than 4 hours).
  • Slow athletes taking the time to stop and drink at all the refuelling stations.
  • For less experienced athletes, working out to “better” sweat and lessen the salt loss through perspiration.
  • Lightweight athletes because the same amount of drink dilutes their blood faster.
  • Women because their weight is on average lower and they are more conscientious of staying hydrated.
  • Athletes drinking more than 1.5L water an hour.
  • Athletes taking certain medicines (non-steroid anti-inflammatories like aspirin, ibuprofen).
  • Warm environmental conditions (and even more so when humidity is high).
  • Races where refuelling stations are frequent and abundant (for example every kilometre).

Our advice for preventing hyperhydration and hyponatremia

  • Do not drink excessively: Drink 1 to 2 mouthfuls every 5 to 10 minutes.
  • Do not drink too much at once.
  • Do not drink too much the night before or hours before your long term activity. 500mL maximum in the hour before the race.
  • Do not drink at all the refuelling stations if you already have your drink.
  • Choose a sports drink with sodium (ideally 460mg of salt per litre), and isotonic. This will limit the risk of hyponatremia.
  • Do not take any salt tablets or pills:

o             Primarily because they will not be absorbed properly due to too much salt in them, which could cause digestive difficulties, nausea and vomiting.

o             Secondly because the salty taste of an over-salted drink can slow down drinking and prevent regular hydration during a sports event.

  • Be careful about recipes for “home made” drinks and jellies because the recommended doses like “1 teaspoon of salt per litre or drink bottle” are often too much. 1 Level teaspoon of salt contains 5g of salt and thus nearly 2000mg of salt per litre, or 4 times the recommended dose.

Salt is therefore essential for endurance athletes. It must be adjusted not only during competitions but also during long distance workouts to prevent hyponatremia.

Sport drinks for athletes are altogether advised because they not only have the ideal amount of sodium, 460mg per litre, but also the advantage of being isotonic to limit the onset of digestive problems.


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