Posted March 31, 2016
By Mike McKenney, MS, ATC
In a previous blog post, I briefly mentioned sodium ingestion plays a significant role in the application of hydration strategies. This is a topic often met with some confusion as there are many different recommendations available to healthcare providers. These recommendations can have a direct effect on the fluid balance of an athlete, such as those from the CDC1 and the FDA.2 With that said, this post is not intended to refute the CDC and FDA recommendations, or downplay potential health risks of excessive sodium ingestion, but rather provide a more refined context on the role sodium plays in the hydration practices of an active and healthy population.
Sodium should not be actively avoided by athletes. It is the primary electrolyte that helps drive thirst and maintain appropriate fluid balance in the extracellular fluid space.3 Repetitive bouts of exercise with insufficient sodium replacement can lead to decreases in plasma volume due to an athlete's inability to retain water. This further reduces an athlete's performance as well as the ability to tolerate exercise in hot environments.4 Exercise-associated muscle cramping (EAMC) is a condition commonly assumed to be the result of decreased sodium levels. However, recent investigations indicate there is no reliable, scientific link between EAMC and sodium loss.5 But if athletes should be ingesting sodium, how much is appropriate to ingest?
According to the CDC1,consuming excessive amounts of sodium will have negative effects on the human body to include increased risk of heart disease and high blood pressure. However, similar to general hydration recommendations, sodium recommendations are made to be broadly applied to the general population. The FDA2 agrees with the aforementioned statement, but adds a caveat to their recommendation (added emphasis is mine): "Sodium is an essential nutrient and is needed by the body in relatively small amounts (provided that substantial sweating does not occur)." As Athletic Trainers (ATs), we often find ourselves in settings where substantial sweating is not only a normal occurrence for our patients, but a daily one, which places them in a population who have different needs.
It should not be assumed that a typical diet will be sufficient to replace sodium in athletes. Sweat sodium concentrations and sweat rates can vary widely6, resulting in the need for individual replacement plans. In situations where fluid loss is great, sodium losses can far exceed standard nutritional recommendations. Currently, it is recommended adults 14 and older should consume about 2.3g of sodium per day.7 However, it has been demonstrated athletes can easily exceed this recommendation in a single training session or game:
- Ice-hockey players can lose 5.7g in a single game8
- Soccer players can lose 2.4g in a single training session9
- Football players can lose up to 17.5g following a two-a-day practice6
Likewise, due to large variations in sweat rate and sweat sodium concentrations, some athletes are perfectly fine with their diet alone. Knowing how much an athlete needs is necessary in order to make an appropriate recommendation, and this can be accomplished with minimally invasive sweat testing services offered by a number of companies. Additionally, replacement can be achieved with the sodium consumed as part of a meal, such as chicken noodle soup,10 or with a number of commercially available products. However, care needs to be taken to understand an athlete’s medical history prior to making any sodium supplementation recommendations in order to account for medical conditions where this practice is potentially contraindicated.
2. http://www.fda.gov/Food/ResourcesForYou/Consumers/ucm315393.htm (Know Your Numbers)
3. Shirreffs S, Maughan R. Volume repletion after exercise-induced volume depletion in humans: replacement of water and sodium losses. Am J Physiol. 1998;274(5 pt2):F868-875.
4. Shirreffs SM, Sawka MN. Fluid and electrolyte needs for training, competition, and recovery. J Sports Sci. 2011;29(S1):S39-S46.
5. Murray D, Miller KC, Edwards JE. Does a reduction in serum sodium concentration or serum potassium concentration increase the prevalence of exercise-associated muscle cramps? J Sport Rehabil. 2015 [Epub ahead of print].
6. Fowkes-Godek S, Peduzzi C, Burkholder R, Condon S, Dorshimer G, Bartolozzi AR. Sweat rates, sweat sodium concentrations, and sodium losses in 3 groups of professional football players. J Athl Train. 2010;45(4):364-371.
8. Godek, S.F., Godek, J.J., McCrossin, J., and Bartolozzi, A.R. 2006. Sweat and sodium losses in professional ice hockey players during a pre-season practice and a game. Med Sci Sports Exerc. 38: S218–S219.
9. Maughan R, Merson S, Broad N, Shirreffs S. Fluid and electrolyte intake and loss in elite soccer players during training. Int J Sport Nutr Exerc Metab. 2004;14(3):333-346
10. Ray ML, Bryan MW, Ruden TM, Baier SM, Sharp RL, King DS. Effect of sodium in a rehydration beverage when consumed as a fluid or meal. J Appl Physiol. 1998;85(4):1329–1336.
About the Author
Mike McKenney is an Athletic Trainer (AT) at Northeastern University in Boston, Massachusetts, where he is the Medical Coordinator for their Division I men’s ice hockey program. Prior to Northeastern University, he served as an AT in multiple settings including secondary schools, Division I athletics and professional cycling; additionally, he worked as an AT who extends the services of a physician for a large orthopedic group. He has also provided services for many organizations to include the Boston Marathon, USA Cycling and USA Volleyball.
McKenney is a hydration and electrolyte replacement consultant for the Atlanta Hawks of the NBA. His professional interests include hydration, electrolyte replacement, thermoregulation in sport and postural restoration. McKenney completed his athletic training education at Gustavus Adolphus College in Saint Peter, Minnesota and master’s degree at North Dakota State University in Fargo, North Dakota. His graduate research was published in the February 2015 edition of the Journal of Athletic Training.