Hyperhydration, rather than dehydration, may pose a greater health risk to athletes, according to two articles in a British medical journal.

Heat-induced dehydration rarely causes athletes to collapse during workouts or competition. In most cases, the culprit is exercise-associated postural hypotension, Tim Noakes, MD, of the University of Cape Town in South Africa, wrote in an article published online in BMJ. The primary treatment should be recovery in a head-down position, not fluid intake.

Misperceptions about dehydration have been driven in large part by marketing of sports drinks, according to Noakes, author of Waterlogged: The Serious Problem of Overhydration in Endurance Sports.

“Over the past 40 years humans have been misled ... to believe that they need to drink to stay ‘ahead of thirst’ to be optimally hydrated,” he wrote. “In fact, relatively small increases in total body water can be fatal.”

A 2% increase in total body water leads to generalized edema that can impair physical and mental performance, he continued. Even greater increases in overhydration can cause hyponatremic encephalopathy, leading to confusion, seizures, coma, and - if not reversed - death by respiratory arrest.

Healthy athletes face “barely any risk” of dehydration during competition in an endurance event. Serious health risks - including inhibition of voluntary motor activity and paralysis - occur only when total body water decreases by 15% or more, which would require 48 hours in the desert with no water.

“Confusion arose when the erroneous belief that all athletes who collapse after suffering from a dehydration-induced heat illness was promoted as part of the false ‘science of hydration,’” Noakes continued. “This dictated that people collapsing needed to drink more fluids during exercise and immediate resuscitation with large volumes of intravenous fluids.

“However, athletes who collapse are neither hotter nor more dehydrated than control runners who complete the same races without collapsing.”

In the second article, BMJ investigative reporter Deborah Cohen traced the focus on hydration - and the burgeoning market for sports drinks - to collaboration between the sports drink industry and academia.

“An investigation by the BMJ has found that companies have sponsored scientists, who have gone on to develop a whole area of science dedicated to hydration,” Cohen wrote. “These same scientists advise influential sports medicine organizations, which have developed guidelines that have filtered down to everyday health advice.”

Coca-Cola and GlaxoSmithKline - distributors of the sports drinks Powerade and Lucozade, respectively - are a partner and a service provider to the 2012 Olympics in London, she noted.

The report, which includes quotes from an interview with Noakes, goes on to describe a variety of industry-driven activities to promote the “science” of hydration, such as:

  Industry-funded websites that provide information on the importance of hydration in sports performance
  Sports drink advertisements that resemble articles from scientific journals
  Grants and gifts to sports medicine organizations and to university-affiliated entities that study hydration
  Journal articles by scientists with financial ties to the sports drink industry (often published without financial disclosures)

Cohen concludes the article with a quote from Noakes about casual runners who consume sports drinks to improve their performance: “If they avoided the sports drink they would get thinner and run faster.”

Primary source: BMJ
Source reference: Noakes TD “Commentary: Role of hydration in health and exercise” BMJ 2012; 344: e4171.

Additional source: BMJ
Source reference: Cohen D “The truth about sports drinks” BMJ 2012 345: e4737.