Fractured fairy tales: hyponatraemia and the American College of Sports Medicine fluid recommendations

Noakes and Speedy,¹ in the article “Case proven: exercise associated hyponatremia is due to overdrinking,” deliver a shot at the 1996 American College of Sports Medicine (ACSM) exercise and fluid replacement position stand² that is off the mark. Much as the popular 1960s’ television cartoon series Rocky and Bullwinkle Show presented Aesop’s fables in “Fractured fairy tales” a key element of the story is missing. The ACSM position stand recommends that athletes should “consume the maximal amount of fluids during exercise that can be tolerated without gastrointestinal discomfort “up to a rate equal to that lost from sweating”, not “drink as much as you can,” as stated in the text of “Case proven.” The recommendation is briefly summarised in the abstract of the position stand, which creates a possibility for misunderstanding or misquoting if one reads only the abstract and not the position stand itself. Reading the entire document is required to avoid a “fractured” message. Attributing “drink as much as you can” to the 1996 ACSM exercise and fluid replacement position stand is a recurring theme in the works of a few authors, but the problem is simply misapplication of the ACSM advice. I have copied the pertinent section of the ACSM position stand to illustrate the recommendations:


 “As such, individuals participating in prolonged intense exercise must rely on strategies such as monitoring body weight loss and ingesting volumes of fluid during exercise at a rate equal to that lost from sweating, i.e., body weight reduction, to ensure complete fluid replacement. This can be accomplished by ingesting beverages that enhance drinking at a rate of one pint of fluid per pound of body weight reduction. While gastrointestinal discomfort has been reported by individuals who have attempted to drink at rates equal to their sweat rates, especially in excess of 1 l/h, this response appears to be individual and there is no clear association between the volume of ingested fluid and symptoms of gastrointestinal distress. Further, failure to maintain hydration during exercise by drinking appropriate amounts of fluid may contribute to gastrointestinal symptoms. Therefore, individuals should be encouraged to consume the maximal amount of fluids during exercise that can be tolerated without gastrointestinal discomfort to a rate equal to that lost from sweating.”

Some confusion may arise from reading only the abstract, which states, “During exercise, athletes should start drinking early and at regular intervals in an attempt to consume fluids at a rate sufficient to replace all the water lost through sweating (ie, body weight loss), or consume the maximal amount that can be tolerated.” In light of the main text, this statement was intended to mean “replace up to sweat losses”. The abstract summary statement apparently opened the door to misinterpretation. The point is clearly stated and correct in the body of the document and leads to the moral of the tale. First, read the entire document, and second, ACSM has cautioned its position stand authors to make absolutely sure their abstracts represent clearly and accurately the main conclusions, because summaries by their nature are incomplete and can lead to confusion or worse. As Noakes was a reviewer of the 1996 ACSM fluid position stand, he should be familiar with the entire position stand.

Although most involved in the care and study of athletes agree that ingesting too much hypotonic fluid, either water or a sports drink, predisposes certain athletes to hypervolaemic hypernatraemic encephalopathy and pulmonary oedema, the exercise-associated hyponatraemia case is not closed. As Dancaster³ demonstrates in his 1971 publication, hypovolaemic hyponatraemia did, and from my clinical experience still does, occur in long duration events, probably as a combined result of sweat sodium and water losses. Eight hyponatraemic cases with 4–7% decreases in body weight in one race, as Dancaster outlines from a relatively cool Comrades Marathon, would be a rarity today, probably because we have changed the culture of fluid replacement since the 1960s and early 1970s when replacement fluids on the sidelines and at races were non-existent. Now fluids are freely available to athletes and there are less cases of severe dehydration than in the past. Fluid availability is good to a point as Noakes and Speedy¹ outline in their paper, but too much of a good thing can be disastrous for a select few.

Although the number of hyponatraemic cases has increased since 1971, mostly from the hypervolaemic class, replacing only your sweat losses remains the best advice today. When giving ranges, whether it is 600–1200 ml/h in the ACSM position stand or 400–800 ml/h as suggested by Noakes, the individual variability in sweat rates leaves some underhydrated and others overhydrated. A prime example is the case presented by Dugas and Noakes⁴ of a woman who repeatedly developed hyponatraemia during prolonged activities and had a sweat rate of 270 ml/h. She was destined to overhydrate with any of the published volume recommendations because she had a sweat rate that fell far below the usual sweat rate ranges during exercise. Replacing sweat losses is her safest route to successful participation, because her kidneys do not respond with appropriate diuresis during activity. The wide variation in fluid requirements across the entire athlete population makes it nearly impossible to give a precise recommendation that includes specific fluid volumes. The best advice still remains to “replace the sweat losses” as outlined in the 1996 ACSM position stand. We are all interested in athlete safety and a fractured misunderstood or mis-stated message does not advance that goal.

ACSM’s exercise and fluid replacement position stand is currently in revision and should be published in the near future with updates that reflect changes in the subject since 1996.