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Sodium Supplementation For Ultra-Endurance Sport: Are You Supplementing Too Much?

Healthy individuals are recommended to consume up to 1.5 grams of sodium per day. However, sodium requirements for athletes differ.

Sodium is an essential nutrient required for many physiological processes including electrolyte homeostasis, nutrient absorption, maintenance of cell plasma volume, acid-base balance, transmission of nerve impulses, and normal cell physiology. Specifically for athletes, sodium contributes to the establishment of the membrane potential of most cells and plays a direct role in the action potential required for the transmission of nerve impulses and muscle contraction.

Ultramarathon runners commonly consume sodium during competitions, believing that sodium losses must be replaced to prevent exercise-associated hyponatremia (EAH), dehydration, muscle cramping, and nausea (Winger et al., 2013).

How much sodium do you lose during exercise?

When we exercise, we sweat. Sweating is a crucial cooling mechanism. As sweat evaporates, it cools the skin’s surface, helping to lower body temperature. However, sweating also leads to fluid and electrolyte loss. The primary components of sweat are sodium and chloride, with potassium, calcium, and magnesium present in smaller amounts. Various factors affect an athlete’s sweat rate, including gender, age, training intensity, environmental conditions and fitness level. The amount of electrolytes lost in sweat also varies.

During exercise, athletes often focus on supplementing sodium to compensate for the loss of electrolytes, primarily sodium and chloride. However, as shown in Table 1, the concentration of most electrolytes in sweat is lower than in blood. This means you will always lose more fluid relative to electrolytes. Therefore, it is critical to prioritise individual fluid consumption first, followed by sodium intake.

Table 1: Electrolyte concentrations (mmol/L) in blood and sweat
ELECTOLYTE BLOOD CONENCTRATIONS FINAL SWEAT CONCENTRATIONS
SODIUM (Na+) 135-145 mmol/L 20 – 80 mmol/L (460 – 1840 mg/L)
CHLORIDE (Cl-) 95 – 110 mmol/L 20 – 60 mmol/L (700 – 2100 mg/L)
POTASSIUM (K+) 2.5 – 5.5 mmol/L 2.5 – 4.5 mmol/L (98 – 175 mg/L)
CALCIUM (Ca2+) < 1.5 mmol/L < 1.5 mmol/L (<60 mg/L)
MAGNESIUM (Mg2+) < 1 mmol/L < 1 mmol/L (<24 mg/L)

Should athletes then prioritise sodium supplementation?

The short answer is that scientists can’t agree and the recommendations differ. To summarise a few position stands:

The Sports Dietitians Australia position statement: It is noted again that exercise-associated hyponatremia is mostly associated with excessive intake of fluid rather than Na+ loss (Hew-Butler et al., 2015). This can be prevented by simply ensuring that fluid intake during exercise does not exceed losses, and it should be noted that ad libitum drinking and drinking to thirst do not necessarily guarantee this (Hew-Butler et al., 2015).

Conversely, the International Society of Sports Nutrition Position Stand: Nutritional considerations for single-stage ultra-marathon training and racing (Tiller et al., 2019) recommends that to reduce the risk of hyponatremia during long-duration exercise, athletes should consume sodium in concentrations of 500–700 mg/L (± 22-30 mmol/L) of fluid [Sawka et al., 2007].

Furthermore, the American College of Sports Medicine (ACSM) recommendations for sodium intake during prolonged training are 300–600 mg/h.

Hoffman & White (2020) concluded that work published in the past several years has demonstrated that sodium supplements are not necessary for the prevention of dehydration during ultramarathon running up to 30 hours (Hoffman & Stuempfle 2014; Hoffman & Stuempfle 2016a) when considering the body mass loss required to maintain euhydration (optimal level of hydration) (Hoffman et al. 2018a, 2018b). Recent work has also demonstrated that sodium supplements are not necessary for preventing EAH (Hoffman and Stuempfle 2015a), muscle cramping (Hoffman and Stuempfle 2015b) and nausea (Hoffman and Stuempfle 2016b) during ultramarathon running.

Scientists can however agree that there is no need to replace all the sodium lost in sweat and a typical sports drink provides sufficient sodium.  Salt tablets and drinks very high in sodium are unnecessary to maintain normal blood sodium levels and no performance benefit is gained.

Although exercise-associated hyponatremia (EAH) is common in ultra-endurance athletes, it is believed to result from overhydration (Hew-Butler et al., 2015). Recommendations to replace all the weight lost during training to prevent dehydration are outdated. A mild degree of weight loss is acceptable, especially in endurance and ultra-endurance events where stored fuels (glycogen, fat, and protein) are metabolized. During these events, additional fluid is also lost through the metabolism of nutrients and respiratory water loss, but this does not significantly affect the athlete’s hydration status.

Research has shown that for events or training sessions lasting more than two hours, 100 % fluid replacement does not improve performance. In ultra-endurance events, it can even increase the risk of hyponatremia (overhydration).

Lastly, there is little evidence that electrolyte deficits are associated with increased occurrence of cramps. Neuromuscular fatigue is a likely cause contributing to cramps because fatigue leads to the disruption of the normal mechanisms of muscle contraction control via neuronal reflexes.

How much sodium should athletes supplement?

Athletes should focus on the following:

  1. Prioritize Fluids and Carbohydrates: Studies have not shown any performance benefits from sodium supplementation, whereas carbohydrates are a well-researched ergogenic aid. Attention should first be paid to the individual amount of fluids and carbohydrates consumed, and only then to the amount of sodium (electrolytes) consumed.
  2. Replace Key Electrolytes: Sodium and chloride are the main electrolytes lost in sweat and are the only ones that must be actively replaced during exercise.
  3. Avoid excessive sodium supplementation: Athletes participating in hot or humid conditions or ultra-endurance events should aim for a sodium intake of 20-40 mmol/L. Isotonic Octane and Octane XTR contain approximately 25 mmol/L of sodium.
  4. Always Combine Sodium with Fluids: Athletes should supplement sodium with fluids to avoid excessive sodium intake. Therefore, it is recommended to avoid cramp blocker tablets or salt tablets.

REFERENCES

Hew-Butler, T., Rosner, M.H., Fowkes-Godek, S., Dugas, J.P., Hoffman, M.D., Lewis, D.P., Maughan, R.J., Miller, K.C., Montain, S.J., Rehrer, N.J. and Roberts, W.O., 2015. Statement of the 3rd international exercise-associated hyponatremia consensus development conference, Carlsbad, California, 2015. British Journal of Sports Medicine49(22), pp.1432-1446.

Hoffman, M.D. and Stuempfle, K.J., 2014. Hydration strategies, weight change and performance in a 161 km ultramarathon. Research in Sports Medicine22(3), pp.213-225.

Hoffman, M.D., Stuempfle, K.J. and Valentino, T., 2015a. Sodium intake during an ultramarathon does not prevent muscle cramping, dehydration, hyponatremia, or nausea. Sports medicine-open1, pp.1-6.

Hoffman, M.D., Stuempfle, K.J., Sullivan, K. and Weiss, R.H., 2015b. Exercise-associated hyponatremia with exertional rhabdomyolysis: importance of proper treatment. Clinical Nephrology83(4), pp.235-242.

Hoffman, M.D. and Stuempfle, K.J., 2016a. Is sodium supplementation necessary to avoid dehydration during prolonged exercise in the heat? The Journal of Strength & Conditioning Research30(3), pp.615-620.

Hoffman, M.D. and Stuempfle, K.J., 2016b. Does oral buffered sodium supplementation reduce nausea and vomiting during an ultramarathon? Research in Sports Medicine24(1), pp.94-103.

Hoffman, M.D. and White, M.D., 2020. Belief in the need for sodium supplementation during ultramarathons remains strong: findings from the Ultrarunners Longitudinal TRAcking (ULTRA) study. Applied Physiology, Nutrition, and Metabolism45(2), pp.118-122.

McCubbin, A.J. and Costa, R.J., 2018. Impact of sodium ingestion during exercise on endurance performance: A systematic review. International Journal of Sports Science8(3), pp.97-101.

McCubbin, A.J., Allanson, B.A., Odgers, J.N.C., Cort, M.M., Costa, R.J., Cox, G.R., Crawshay, S.T., Desbrow, B., Freney, E.G., Gaskell, S.K. and Hughes, D., 2020. Sports dietitians Australia position statement: nutrition for exercise in hot environments. International Journal of Sport Nutrition and Exercise Metabolism30(1), pp.83-98.

Sawka, M., Burke, L., Eichner, R., Maughan, R., Montain, S. and Stachenfeld, N., 2007. American College of Sports Medicine exercise and fluid replacement position stand. Med. Sci. Sport. Exerc39, pp.377-390.

Tiller, N.B., Roberts, J.D., Beasley, L., Chapman, S., Pinto, J.M., Smith, L., Wiffin, M., Russell, M., Sparks, S.A., Duckworth, L. and O’Hara, J., 2019. International Society of Sports Nutrition Position Stand: Nutritional considerations for single-stage ultra-marathon training and racing. Journal of the International Society of Sports Nutrition16, pp.1-23.

Winger, J.M., Hoffman, M.D., Hew-Butler, T.D., Stuempfle, K.J., Dugas, J.P., Fogard, K. and Dugas, L.R., 2013. The effect of physiology and hydration beliefs on race behavior and postrace sodium in 161-km ultramarathon finishers. International Journal of Sports Physiology and Performance8(5), pp.536-541.

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