Too Much Water Bigger Threat Than Too Little
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)
Noakes and Cohen had no relevant disclosures.
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.
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Little Back Up for Sports Drink, Product Claims
More than half of the sports products reviewed with performance-enhancing claims had no references to studies supporting those claims (52.8%), according to Carl Heneghan, MD, of the University of Oxford in England, and colleagues.
The studies mentioned by those products that did provide them had a high risk of bias in 84%. In addition, 41.9% of the studies had no randomization, allocation concealment was apparent in 6.8% of studies, and only 27% of the research included blinding of participants, investigators, or outcome assessors, Heneghan and co-authors wrote online in BMJ Open.
The study measured the quality of support for claims made in online advertisements about 104 sports-related products, such as sports drinks, supplements, footwear, clothing, and devices with performance- or recovery-enhancing qualities attributed to them.
Researchers found 431 claims about the products online on the manufacturers' websites after reviewing 1,035 web pages related to those products. They recorded data on each product's category, number and type of performance claims attributed to it, references to claims made about it, and qualifiers related to claims (such as "should be used in conjunction with a healthy diet"). If a reference paper supporting a claim was not available, the company was contacted and asked for any supporting literature.
Literature, if available, was evaluated for quality through the Center for Evidence-Based Medicine Levels of Evidence and Cochrane method of risk of bias, as well as whether participants were professional athletes or not.
Of 431 claims made, only 74 studies referenced by those claims were appropriate for critical appraisal.
There were 2,031 participants between the 74 studies, two of which made up a quarter of total participants (total n=505). Around half of total participants were classified as "regular people who exercise" (48.6%), another 39.2% were considered endurance or serious athletes, and 10.8% were considered professional athletes.
A total of three of the studies (4.1%) were judged to be of "high quality and at low risk of bias," and none of the studies included systematic review, Heneghan and colleagues wrote.
"Half of all websites for these products provided no evidence for their claims, and of those that do, half of the evidence is not suitable for critical appraisal," they added.
Most of the studies reported a surrogate, rather than direct, outcome of performance or recovery (83%, 95% CI 73% to 92%) and two studies repeated the study protocol intervention (2.7%, 95% CI 0% to 25%). Only 11% of studies reported study limitations (95% CI 0% to 33%).
In addition, small samples and laboratory environments had a negative effect of the validity of study findings, the investigators wrote.
The authors noted several limitations in their own review, including the possibility that the evaluated products were "at the worst end of the spectrum," subjective criteria to determine whether a product was billed as "performance-enhancing," and a lack of investigation into the heterogeneity of effects or publication bias.
Based on these results, current research by sports product manufacturers does not sufficiently inform potential customers of risks and benefits to using products sold with performance-enhancing claims, they concluded.
The authors had no conflicts of interest to declare and received no funding support.
Primary source: BMJ Open
Source reference:
Heneghan C, et al "The evidence underpinning sports performance products: a systematic assessment" BMJ Open 2012; DOI: 10.1136/bmjopen-2012-001702.
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