Changes in body mass alone explain almost all of the variance in the serum sodium concentrations during prolonged exercise. Has commercial influence impeded scientific endeavour?


Journal Title (Medline/Pubmed accepted abbreviation): Br. J. Sports Med.
Year: 2011
Volume: 45
Page numbers:475-477
doi (if applicable): 10.1136/bjsm.2010.075697

Summary of the article

 Exercise-associated hyponatremia encephalopathy (EAHE) is swelling of the brain as a result of dangerously reduced sodium concentrations in the body, as a result of drinking too much water.  In a 1991 report, excess water consumption was shown to be the cause, as it was shown that athletes that suffered EAHE lost the same amount of sodium during a marathon than their healthy counterparts.  The author claims that, due to commercial interest (specifically, by the Gatorade company), that 1) the risk of hyponatremia was downplayed and the dangers of dehydration are emphasized in the athletic community and in our society and 2) if EAH is mentioned, people erroneously say that only water will cause EAH, not electrolyte-enriched sports beverages.

The American College of Sports Medicine (ACSM) reports a “Position Stand”, headed by expert scientists in the sports nutrition community that provide recommendations for athletes.  The 1996 ACSM Position Stand encouraged athletes to drink “as much as tolerable”, which seemingly ignored the research that this author has published.  The author stated that this stand caused an “epidemic” of EAH (though he only cited one of his own papers published 4 years prior).

The author reanalyzed published research data from studies performed by Gatorade scientists and showed that over-ingestion of water or an electrolyte (sodium and potassium) solution that has up to 1.67 times the electrolyte concentration as Gatorade will result in lower serum sodium concentrations after exercise (p = 0.035).  The author also illustrated a clear correlation between change in body mass and post-exercise blood sodium concentration; the more weight lost during exercise, the higher the blood sodium level (likely due to water loss during exercise).  Drinking water or an electrolyte beverage, especially enough to cause one to gain weight after exercise, causes blood sodium concentrations to be lower than those who did not drink water, thereby putting one at risk for EAH.  The conclusion from his reanalysis of their data is that it is definitely possible to drink too much fluid, and adding electrolytes only slightly rectifies the situation.  It is healthy to lose some weight during exercise from sweat losses; over consuming fluid can put one at risk for EAH and EAHE.


Interpretation of findings/Key practice applications

Overconsumption of water or electrolyte-rich sports beverages can increase the risk for EAH and EAHE. The author claims that, although these findings have been shown in the scientific literature, companies and associations can distort or overshadow the findings in order to sell sports products and/or make financial gains. While exercising, especially in hot conditions, it is important to drink fluids to replace what was sweat out but not drink more fluid than that. Ideally, one would monitor weight loss during exercise and drink accordingly. However, this is not practical in most cases.
 
Limitations

The topic of EAH is controversial and Noakes has stimulated much scientific discussion and debate in the past regarding his viewpoints. Such controversy may or may not be justified, but it is important for the reader to be aware of this.

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