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THE TRUTH ABOUT SPORTS DRINKS Sports drinks are increasingly regarded as an essential adjunct for anyone doing exercise, but the evidence for this view is lacking. Deborah Cohen investigates the marketing of the science of hydration

rehydrate; drink ahead of thirst; train with the New York marathon. Manufacturers According to Noakes, the sports drink industry your gut to tolerate more fluid; your of sports shoes and the drink and nutritional needed to inculcate the idea that fluid intake was brain doesn’t know you’re thirsty—the ­supplement industries spotted a growing market. as critical for athletic performance as proper train- public and athletes alike are bombarded One drink in particular was quick to capitalise ing. “It became common for athletes to state that with messages about what they should on the burgeoning market. Robert Cade, a renal the reason why they ran poorly during a race was Pdrink, and when, during exercise. But these drink- physician from the University of Florida, had pro- not because they had trained either too little or too ing dogmas are relatively new. In the 1970s, mar- duced a sports drink in the 1960s that contained much, but because they had become dehydrated. athon runners were discouraged from drinking water, sodium, sugar, and monopotassium phos- This was a measure of the success of the industry fluids for fear that it would slow them down, says phate with a dash of lemon.1 2 Gatorade—named in conditioning athletes to believe that what they Professor Tim Noakes, Discovery health chair of after the American Football team, the Gators, that drank during exercise was as important a deter- exercise and sports science at Cape Town Univer- it was developed to help—could prevent and cure minant of their performance as their training,” sity. At the first New York marathon in 1970, there dehydration, heat stroke, and muscle cramps, he says. was little discussion about the role of hydration—it and improve performance, it was claimed.2 Indeed, after the “invincible” Australian was thought to have little scientific value. The first experimental batch of the sports cricket team lost the 2005 Ashes test series to So how did the importance of hydration gain drink cost $43 (£28; €35) to produce but has rivals England, a research fellow at the A­ustralian traction? An investigation by the BMJ has found spawned an industry with sales of around Institute of Sport (AIS) started to monitor players’ that companies have sponsored scientists, who £260m a year in the UK alone—and consump- levels of dehydration.6 have developed a whole area of science dedicated tion is increasing steadily. “The buzz around The previous year (2004), the institute had to hydration. These same scientists advise influ- sports and energy drinks is here to stay. This has entered a partnership with Gatorade. The AIS’s ential sports medicine organisations, which have remained the fastest growing sector in the UK first Gatorade fellow, Kelly Drew, conducted a developed guidelines that have filtered down to soft drinks market,” an industry report suggests.3 study on hydration among the cricketers, taking everyday health advice. These guidelines have In the US the market is even bigger. In 2009, urine samples and testing their sweat. “We do influenced the European Food Safety Authority, f­orecasters, Mintel, valued it at $1.6bn, and the know that 50% of them turned up today dehy- the EU agency that provides independent advice market is projected to reach $2bn by 2016.4 drated, which is not a good sign,” she said.6 on the evidence underpinning health claims The rapid rise in consumption is hardly The AIS is just one organisation backed by relating to food and drink. And they have spread surprising—sports drinks have the might of Gatorade—other powerful sports medicine fear about the dangers of dehydration. multinationals behind them. PepsiCo bought organisations also receive funding from drinks Much of the focus on hydration can be traced Gatorade in 2001 and both Coca-Cola and companies. The US National Athletic Trainers’ back to the boom in road running, which began GlaxoSmithKline (GSK) make sports drinks— Association (NATA), a representative body of Powerade and Lucozade respectively. The com- sports health professionals with over 35 000 panies are a partner and service provider to the members, works closely with Gatorade. London 2012 Olympics. The company has taken out advertisements in bmj.com The key behind the rise in consumption of NATA’s newssheet that look like academic papers. ЖЖFor more in sports drinks lies in the coupling of science with These “research adverts” are just one example of depth interviews marketing. What started life as a mixture of sim- how companies promote the idea that the benefits watch a video at ple kitchen foodstuffs has become an “essential of their drinks are based on decades of thorough bmj.com/multimedia piece of sporting ­equipment.”5 scientific research.

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Selling science Taking on thirst Lucozade’s transformation Gatorade documents from 2010 show that sales Perhaps one of GSSI’s greatest successes was to Although it is now staff are encouraged to watch an internal video undermine the idea that the body has a perfectly associated with sport, called “Selling the Science” and told to “make good homeostatic mechanism for detecting and Lucozade had a sickly start sure consumers understand the science behind responding to dehydration—thirst. “The human in life. Initially developed by Gatorade.” Promotion also hinges on the notion thirst mechanism is an inaccurate short-term a pharmacist in Newcastle, that sports drinks are among the “best researched indicator of fluid needs . . . Unfortunately, there Glucozade—as it was then called—was launched as food products on the planet,” Bob Murray, a is no clear physiological signal that dehydration is a glucose supplement to former director of the Gatorade Sports Science occurring,” Bob Murray from the Gatorade Sports help people recover from 7 13

Institute wrote in 2001. Science Institute declared in 2008. Others have common illnesses and was PICTUREARCHIVE/GETTYPOST/HULTON And they’re not the only ones—when GSK followed suit. Powerade say: “Without realising, soon snapped up by Beecham (now part of GSK’s reshuffled its entire communications department you may not be drinking enough to restore your Nutritional Healthcare division). But illness doesn’t earlier this year, it said a key part of its strategy fluid balance after working out.”14 sell in quite the same way as strength and health. The Lucozade that is familiar today was effectively would be promoting the science behind its prod- And the International Olympic Commit- created in 1983 by UK branding agency Ogilvy & ucts. “The science that goes into our brands is a tee’s nutrition advice for athletes —published Mather. It was relaunched with British Olympic competitive advantage. Lucozade, for example, is in 2003 and updated in 2008 in conjunction gold medal winner Daley Thompson under the subject to more than 100 clinical trials,” a spokes- with P­owerade—doesn’t mention thirst once, proposition that energy and empowerment were a person said.8 9 The company has suggested that even though it includes advice on fluid intake. stronger sell than recovery. the “market is all about credibility.”10 “D­ehydration impairs performance in most In recognition of this, GSK set up the Lucozade events, and athletes should be well hydrated gers of d­ehydration and of the importance of Sports Science Academy (LSSA) in 2003, compris- before exercise,” it says in its booklet, Athletes’ adequate fluid intake. Water is not the best fluid ing a sports nutrition website, links with leading Medical Information.15 for rehydration, either during or after exercise,” universities, and a high-tech gym at the com- Athletes are bombarded with different advice they wrote in an article published in the British pany’s headquarters.10 Marketers intended that and given complex algorithms to calculate their Journal of Sports Medicine.22 bottles of the drink would be stamped with the individual hydration needs. They are told, for In America, the sports drinks industry also LSSA insignia to reaffirm the scientific credibility example, to rehydrate with a pint for every pound made a push into the area of clinical science. In when sports nutrition toolkits were handed out in body weight lost—a drop of 2% is considered a 1992, the American College of Sports Medicine— to gym instructors to educate them in the use of cause for concern. They are also told how to cal- the “premier organization in sports medicine and Lucozade Sport products. 10 culate their sweat rate and to check the colour of exercise science” with over 45 000 members— Indeed, just as drug companies have appointed their urine (box).15 16 accepted a $250 000 donation from Gatorade. key opinion leaders to influence doctors’ prescrib- This advice has filtered down to healthcare Four years later, in 1996, the American C­ollege ing patterns, sports drink and supplement com- organisations giving advice to patients playing of Sports Medicine produced guidelines that panies seek to work with gyms and instructors. sport. Diabetes UK, for example, advises people: adopted a “zero % dehydration” doctrine, advis- Virgin Active has a partnership with Powerade, “Drink small amounts frequently, even if you are ing athletes to “drink as much as tolerable.”23 for example,11 and the GSK owned supple- not thirsty— approximately 150 ml of fluid every This guidance grew out of a roundtable meeting ment brand, Maximuscle, 15 minutes—because dehy- in 1993 “supported” by Gatorade.24 has a partnership with LA “The problem was industry dration dramatically affects Half the guideline’s authors either worked with F­itness.12 wanted to sell more performance.”20 the US military—the world’s biggest customer of Like GSK, Gatorade has products so it had to say that Studies suggest that thirst Gatorade—or had a financial relationship with pushed heavily on the sci- thirst was not adequate” is a more reliable trigger. A the Gatorade institute. Over time, these authors ence. In 1985, Gatorade, meta-analysis of data from would strengthen their relationship with the then owned by Quaker Oats, set up its Gatorade cyclists in time trials concluded that relying on college, with Lawrence Armstrong and Michael Sports Science Institute (GSSI) in Barrington, thirst to gauge the need for fluid replacement was Sawka—who both work for the United States Army Illinois, to conduct and publish research and to the best strategy.21 “The problem was industry Research Institute of Environmental M­edicine— educate sports health professionals and athletes wanted to sell more products so it had to say that becoming senior editors of the c­ollege’s journal on sports nutrition and exercise science. thirst was not adequate,” Noakes says. And he in the past 10 years. Just as drug companies held sponsored sym- should know—Noakes developed a sports drink The college’s ex-president, W Larry Kenny, posiums in exotic locations, Quaker Oats held with South African company, Leppin, in the 1980s. even wrote that they cautioned against physically invitation only annual conferences in locations active people “letting their thirst guide them.”25 around the world . Attendees included advisers Link ups with industry The 1996 guidance stood until 2007, when in to the world’s most influential sports authorities. Academics were in the vanguard of the drive updated guidance the college acknowledged that Indeed, the editors of a sports medicine against thirst and the promotion of the dangers people should drink according to thirst. However, book on performance were among them. of dehydration. In 1993, a group of experts led it still promoted the idea that people should lose Ron Maughan, Louise Burke, and Edward by Ron Maughan, professor of sport and exer- no more than 2% of body weight during exercise, Coyle, co­editors of Food, Nutrition and Sports cise nutrition at Loughborough University and a and this remains the position in the published lit- P­erformance II: The International Olympic member of GSSI’s sports medicine review board erature—although how people are meant to know C­ommittee Consensus on Sports Nutrition, pub- since 1990, produced a consensus statement at how much weight they are losing while exercising lished in 2004, all have financial links (personal a meeting funded by Isostar, a sports drink then isn’t made clear.26 or institutional) to Gatorade and their book was owned by drug company, Novartis. “There is a Three of the six authors of the updated guid- supported by Coca-Cola, the makers of Powerade. need to make athletes more aware of the dan- ance declared major financial conflicts of interest.

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Randy Eichner and Nina Stachenfeld had finan- guidance. A spokesperson said: “ACSM follows with sport has become a real concern—that of cial ties to Gatorade, and Ronald Maughan had best practices regarding corporate relationships, exercise associated hyponatraemia. There have received funding from Coca-Cola and GSK, as well disclosures, and conflicts of interest,” adding been 16 recorded deaths and 1600 people taken as being on the GSSI review board. Louise Burke that the college has “demanding requirements critically ill during competitive marathon run- had no personal financial ties, although her insti- in the areas of disclosure and avoidance of con- ning because of a drop in their serum sodium (see tution, the AIS, received funding from Gatorade. flict of interest.” The college also maintains that linked commentary).27 The other two authors, Michael Sawka (chair of the “chairs of both the 1996 and 2007 Position The cause of this is keenly debated—in par- the committee) and Scott Montain, worked for Stands on fluid replacement were US federal gov- ticular whether it is the volume or type of fluid the US military and had attended the exclusive ernment employees with no professional affilia- consumption that is most to blame. The largest Quaker Oats meetings in the 1990s. Even two of tions with the sports beverage industry.” prospective study, conducted in a diverse group the five reviewers—Michael Bergeron and Mark Despite all the guidance about the dangers of of marathon runners (funded by the National Hargreaves—declared financial links to Gatorade. dehydration during exercise, Arthur Siegel, asso- Institutes of Health and published in the New There is nothing wrong with working with ciate professor of medicine at Harvard U­niversity England Journal of Medicine), found no associa- industry. Indeed, a UK parliamentary select com- and adviser to the Boston marathon, says that tion with the composition of fluids consumed and mittee heard in 2006 that “sports science tends to there is no evidence that anyone doing a mara- concluded that it is the volume of fluid that is the be a Cinderella subject, which does not have the thon has ever died from it. “Dehydration has main factor leading to hyponatraemia.28 drivers. A lot of the money does come from the gotten all the press and attention partly because According to lead author Christopher Almond, drinks industry and so on but it cannot be entirely of sports medicine associations who have assistant professor of paediatrics at Boston independent.” Links with industry are also seen endorsed the dangers of dehydration, but in fact Children’s Hospital: “The available evidence as a badge of honour. dehydration is not life threatening,” Siegel says. indicates that the most effective way to prevent However, Paul Laursen, adjunct professor at Fluid is freely available in the races should a hyponatremia during marathon running is to the Sports Performance Research Institute in New runner need to drink—they are not stranded in the avoid a positive fluid balance.”28 Zealand, thinks that people with conflicts of inter- desert with no access to fluids, he says. A literature review in a nephrology jour- est shouldn’t be writing guidance. “It [dehydration] is a normal biological nal also backed this up saying there is no “Those people would say that ‘we’ve done all response to exercise. You lose water; you get evidence that “consumption of sports drinks the research, so we know the subject’. You need thirsty; you drink. End of story,” Noakes adds. (­electrolyte-containing hypotonic fluids) can people who are more objective than that—who He is, however, considered maverick in his views. prevent the development of exercise associated can put the studies into context and account for hyponatraemia.”29 However, companies are keen important limitations to the research,” he says. Hyponatraemia to imply that it is water that is the problem. The BMJ asked the college why it chose peo- Against this background of what Noakes says is Coca-Cola, for example, acknowledges that ple with such conflicts of interest to produce its disease mongering, a genuine illness associated hyponatraemia is a cause for concern “for anyone doing endurance sports,” but says that this is due SCAREMONGERING OVER THE EFFECTS OF DEHYDRATION to the failure to “replace the sodium lost through The ACSM guidelines also she says, “We don’t understand that address the relation between sweat or drinking a very large volume of very low- emphasised the relation between what causes exertional heat exertional heat related illness and sodium beverages such as water.” The Powerade dehydration and serious illness stroke.” hydration. webpage describing hyponatraemia does not in sport saying that it causes Studies that have shown that From a health perspective, mention that it can also happen if sports drinks heat exhaustion, heat stroke, dehydration causes heat illness, Fowkes-Godek worries that if 30 muscle cramps, and exacerbates she argues, have been set up to people are going to be fooled are consumed. The company has subsequently rhabdomyolysis. As well as a few show it. Paul Laursen agrees. into thinking that drinking fluids said it has updated the advice on its website “to laboratory studies, the ACSM “What is done in a lab doesn’t is going to stop them getting ensure that it is clear that athletes should not over draws on findings that dehydration always turn out to be true in heatstroke, they won’t take consume any liquids.” was present in 17% of hospital outdoor conditions. Studies in other preventive measures. But the message has filtered down. “To prevent admissions for heat stroke in the hydration are often conducted This advice has been picked up US military and a similar number in a climate chamber without widely. NHS Choices website hyponatremia and electrolyte imbalances, ath- in Israel.24 It did not conduct a appropriate airflow. They typically says that dehydration in exercise letes should replace lost body fluid with drinks systematic review on the area. don’t use a good fan, so the ability “is the primary cause of heat that contain electrolytes, such as sports drinks,” 50 Sandy Fowkes-Godek, director of to remove heat from the body is exhaustion.” MedicineNet website says.31 the HEAT Institute and a professor reduced, and core temperature Disease mongering is a well of sports medicine at West Chester rises. While this might be what documented phenomenon in 51 Outreach to schools University, has conducted dozens happens in an indoor fitness class, healthcare, and Noakes suggests of studies on National Football it isn’t applicable to what goes that industry has followed a similar The industry push has not stopped with adults League players and failed to show on outside. But companies have pattern with dehydration and participating in sports. GSK has developed that dehydration has an effect on taken this lab finding and made it exercise. an educational outreach programme called core temperature. “It’s a scare gospel,” he says. “When industry wanted to sell S­cientists in Sport (www.scientistsinsport.com) tactic that has worked very well,” A review in the BJSM supports more product it had to develop a as part of its involvement in the Olympic anti­ this. “There are very few recent new disease that would encourage well controlled exercise physiology people to overdrink,” he said doping operations. The programme includes studies of heat and exercise in adding: “Here’s a disease that you materials for “GSK Ambassadors to take into children that are directly applicable will get if you run. Here’s a product schools, and free classroom resources.” to real world field conditions,” it that is going to save your life. That’s 49 One lesson looks at osmosis and water: “Dur- says. Indeed, a spokesperson exactly what they did. They said ing intense exercise, heavy sweating removes water from Gatorade confirmed that there dehydration is a dreaded disease have been no systematic reviews of exercise.” and salts from the body. If large quantities of water alone are consumed, this will dilute the normal

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concentrations of sugars and ions in the blood “P” CHARTS AND URINE TESTS and tissues. Water will enter, by osmosis, and stop The science of dehydration has led levels by studying the colour of the muscles, nerves and the brain from working to another widely held belief that their urine.17 properly. In extreme cases, water intoxication can is not based on robust evidence— The Mayo Clinic’s online occur and may lead to death,” it says. Students are that the colour of urine is a good guidance to patients also suggests then asked which drinks are closest to being isot- guide to hydration levels. urine is a good guide of hydration. JAVIERLARREA/GETTY onic and whether sports drinks justify their prices. Like athletes, British soldiers “Unfortunately, thirst isn’t always are told to check their urine. The a reliable gauge of the body’s need assessed the predictive value of GSK maintains that the programme does not Ministry of Defence signed a for water, especially in children urine colour as a diagnostic test. mention its sports drink. However, it admits that £1.5m three year deal with GSK and older adults. A better indicator “There is a lack evidence for the the introduction to the osmosis lesson—as quoted in 2005 to supply soldiers with is the color of your urine: Clear or widely recommended practice above—could be “made more relevant to the sub- Lucozade. “It is only recently that light-colored urine means you’re of assessing hydration status by ject.” “We are therefore going to update this sec- we have started to examine the well hydrated, whereas a dark looking at the colour of urine,” it suggests.19 tion,” a spokesperson told the BMJ. science behind what our soldiers yellow or amber color usually drink,” the defence secretary, signals dehydration,” it says.18 “The limited evidence shows that But efforts to encourage children to drink John Reid, said at the time. However, a review of the only first morning urine colour sports drinks do not end there. This year, The drink’s packaging includes evidence by Oxford University’s can be reliably used to assess ­Gatorade and the NATA united to declare 11 July a “P chart,” a colour code allowing Centre of Evidence Based Medicine dehydration and rehydration,” the first annual National Recovery Day for high soldiers to check their hydration linked to this investigation has it adds. school athletes in the US. This was “to focus the attention of athletes on the importance of proper funded by Gatorade or included authors with in four adults drink sports drinks at their desk, athletic recovery.” Children were told to “drink financial ties.35 The Institute of Medicine, how- thereby consuming unnecessary calories.39 It 16-24 ounces of fluid with sodium for each pound ever, says: “Thirst and consumption of beverages urges that people should be encouraged to drink of body weight lost during exercise following a at meals are adequate to maintain hydration.”36 water rather than sugary drinks.39 Sports drinks workout or game.”32 A spokesperson for Gatorade also confirmed companies, however, promote the notion that Many schools in the UK now encourage chil- that there were no systematic reviews on hydra- their products are a superior source of hydration. dren to stop every 15-20 minutes during exercise tion in children. Instead, it pointed to three posi- In its guidelines to casual runners taking part to drink. Football teams also instruct children to tion papers that consider the relation between in the Lucozade sponsored national UK event bring a bottle—no football field is seen without a exertional heat related illness and hydration. Parkrun—Lucozade say that “water alone isn’t colourful array of sports drinks. These were from the ACSM and NATA and cite enough to maintain hydration.”40 Powerade’s This practice may be one that originated with “carbohydrate-electrolyte solutions as one of website also suggests “Water is not enough.” Gatorade. In 2000, a former professor of paediat- many potential preventative steps.” “Water doesn’t have the performance benefits of rics at McMaster University in Canada, Oded Bar- In the UK, Maughan took a similar view. He a sports drink,” it says.41 Or, who was also a member of the GSSI medicine wrote in 2001: “Children are particularly likely to However, this is permitted. Earlier this year, review board, promoted the need for children to forget to drink unless reminded to do so,” adding the UK’s Advertising Standards Authority (ASA) stop during sporting activi- that “mild levels of dehydra- rejected a complaint against Powerade for tele­ ties in order to drink. “Children are particularly tion and hyperthermia will vision advertisements featuring Olympic hep- “One should make certain likely to forget to drink reduce exercise capacity.”7 tathlon medal hopeful, Jessica Ennis, that said, that children arrive fully unless reminded to do so” This advice was soon “Powerade ION4 hydrates better than water.” 42 hydrated for a practice ses- adopted by groups lobbying sion or for competition and enforce drink pauses for increased attention to hydration in schools. How good is the evidence? every 15-20 min during prolonged activities, even In the UK, an expert group on hydration was Companies claim that the sodium in sports drinks when the child does not feel thirsty. If necessary, launched in June 2005, supported by the British stimulates thirst, resulting in the consumption rules of the sport should be modified to facilitate Soft Drinks Association, with the “goal of improv- of a higher volume of fluid and better retention periodic drinking,” he wrote in 2000.33 That same ing the nation’s hydration.” Maughan was a key compared with drinking water. Their claims also year he was the main consultant to the American adviser.37 hinge on the physiological observation that the Academy of Pediatrics guidance on heat illness “If children have no understanding of why carbohydrate content of sports drinks aids water and exercise.34 they need to drink frequently, and little or no absorption from the small intestine. Consumers “Children frequently do not feel the need to encouragement is given, their health, wellbeing are told that another benefit is the taste to encour- drink enough to replenish fluid loss during pro- and performance may be at risk,” the group’s age higher fluid intake. longed exercise. This may lead to severe dehydra- report concludes. It also laments the “demonisa- The ASA’s judgment in favour of Powerade was tion,” it said, adding: “A major consequence of tion of vending machines” in schools.37 revealing. Despite over 38 years of research, there dehydration is an excessive increase in core body was no published meta-analysis of studies in this temperature.” War on water area.42 But the reason for this lack of evidence Updated advice in 2011 had Michael Bergeron— The promotion of hydration has created a bat- is clear, says Noakes. “A commercial company who has financial ties to Gatorade— as the main tle ground for the fight between bottled water would never do research that it was not certain consultant and one of the lead authors. “Appro- companies and the sports drinks industry. While of the answer before it did the study,” he says. priate fluid should be readily accessible and con- they both agree about the need to drink plenty of Yet Coca-Cola, GSK, and PepsiCo maintain sumed at regular intervals before, during, and after fluids,38 there is disagreement on what that fluid that the scientific evidence supports their case— all sports participation,” it added giving specific should be. and they’re not the only ones. In 2006, the details about sweat replacement and amounts to The Natural Hydration Council—which repre- European Union adopted new regulation that drink. All references to this were to studies either sents the bottled water industry—warns that one aimed “to ensure that consumers are not misled

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by u­nsubstantiated, exaggerated or untruthful past methods, it said it “now uses an independ- Marketing to athletes or ordinary people? claims about foodstuffs.” The European Food ent expert consultant in meta-analysis process.” Noakes has other concerns about the evidence. Safety Authority (EFSA) was charged with assess- When the Institute of Medicine analysed the He questions how generalisable the results are ing the evidence supporting health claims. same dataset they concluded that “many of the to the public. The studies feature highly trained Two related to sports drinks have been upheld: questions raised about the requirements for and volunteers who sustain exercise at high intensity that they hydrate better than water and that they recommended intakes of these electrolytes and of for long periods. “They are never going to study help maintain performance in athletes doing water cannot be fully answered because of inad- a person who trains for two hours per week, who endurance exercise. This judgment did not apply equacies in the present database.”44 walks most of the marathon—which form the to the ordinary person going to the gym or chil- In their determination to show that a solution majority of users of sports drinks.” dren playing football for an hour a week, Albert of salt and sugar can produce a beneficial effect, Yet it’s precisely these people that companies Flynn, chair of EFSA’s dietetic products, nutrition, companies have funded hundreds of studies over are targeting. Kelly Brownell, director of the and allergies panel, told the BBC. the past 40 years. The BMJ asked several compa- Rudd Center for Food Policy and Obesity at Yale Because EFSA has reviewed the literature, com- nies for lists of these studies (see box for overview University has studied the way sports drinks are panies say the evidence supporting the perform- of research). GSK was the only one willing to pro- marketed. “They are marketed through a general ance benefits of sports drinks is “very strong.” vide such a list, comprising references to the “100 route rather than just in runners’ magazines, But an analysis of the studies submitted to EFSA clinical trials” that suggest its sports drinks have which shows they actually want a broad audi- accompanying the investigation does not uphold important benefits. Gatorade did not respond, ence,” he says. this view. It also finds a troubling circularity in and Coca-Cola sent a detailed response explain- Not all companies shy away from this descrip- the industry influenced evidence base—and this ing how their drink works.45 An accompanying tion of their activities. John Brewer, director of the does not just apply to the funding of the studies. analysis of the studies found that the quality of Lucozade Sport Science Academy, told a parlia- EFSA also says it relied on the American College the evidence was so poor that it was impossible mentary select committee in 2006 that “It is really of Sports Medicine’s 2007 review on hydration.43 to draw firm conclusions about the effects of the looking to get elite endorsement for high quality The BMJ asked the college about its methodology. sports drink (box).9 products that would then be preferred by the con- While not providing substantive comment on the sumer at the mass market level.” But GSK’s response suggests it would prefer not JOURNALS’ LINKS TO INDUSTRY to be viewed in this light. A spokesperson told the While many journals have drafted the ACSM’s 1996 “zero% Science Advisory Board of the BMJ: “Lucozade Sport is for adults who train and scientists on their editorial dehydration” guidance on fluids. GSSI, is a consulting editor for the take part in sport and other vigorous physical boards who have links with This was based on a roundtable Journal of Applied Physiology— the manufacturers of sports funded by Gatorade. Sawka has along with Sawka. This journal exercise and this is stated on the bottle.” The com- drinks—including the BMJ Group’s been, and continues to be, a is owned by the American pany also says that Lucozade is not marketed to BJSM—some have such people in speaker at Gatorade sponsored Physiological Society, which has children under 16. However, last year GSK turned prominent editorial roles. events since 1989. It is not clear if financial links to Gatorade. to pop stars Tinie Tempah and Blink 182 drum- The one with the biggest he receives funding directly. Another prominent editor of mer, Travis Parker—both popular with younger reach is Medicine and Science Ron Maughan, is also a Medicine and Science in Sports in Sports and Exercise. It’s senior editor of the journal. He and Exercise was Oded Bar-Or, children— to become “brand ambassadors” and 46 owned by the American College has a longstanding financial a professor of paediatrics who attract “sporty teenagers.” of Sports Medicine, which relationship with Gatorade, as had a longstanding financial has a longstanding financial well as with Coca-Cola and GSK. relationship with GSSI. He has Influence over journals relationship with Gatorade and Maughan has played senior been a key consultant to the Another problem with the research is transpar- now Powerade. Since 1999, there editorial roles on several other American Academy of Pediatrics ency. Even though a large proportion of the has been a steady increase in the journals over the past 20 years on its hydration strategy. number of Gatorade affiliated including the BJSM, Nutrition, Most of the scientists identified studies have been conducted by scientists with scientists who are editors or on the European Journal of Applied as being on the GSSI board have financial ties to Gatorade (PepsiCo), GSK, and the editorial board. Over the past Physiology, and the Journal of prominent roles in journals. Even Coca-Cola, the authors’ individual conflicts of 12 years, the editors in chief have Sports Sciences, the official its global senior director, Asker interest are either not published or not declared. been Kent Pandolf and Andrew journal of the British Association Jeukendrup, professor of exercise Conflicts of interest also exist within the key jour- Young—both of whom work of Sports and Exercise Science, metabolism at Birmingham for the US military, Gatorade’s which has a financial relationship University, is an editor of the nals in sports medicine—GSSI funded scientists biggest customer, and they with Gatorade.52 European Journal of Sport pepper their editorial boards and editorships. have been instrumental in the Maughan is also coeditor of Science—the official journal of Around half of the studies supplied by GSK science of hydration. Pandolf the International Journal of Sport the European College of Sport appeared in four journals—the Journal of Applied has been a speaker at invitation Nutrition and Exercise Metabolism Science. His biography states Physiology (20), Medicine and Science in Sports only GSSI conferences. Another with Louise Burke who works at that “he has been a member of senior editor, Michael Sawka, the Australian Institute of Sport, the advisory editorial board of the and Exercise (24), International Journal of Sport was chair of the committee who which has a partnership with Journal of Sports Sciences, and Nutrition and Exercise Metabolism (11), and the Gatorade. This journal also has served on the editorial board of Journal of Sports Science (9). Several of these several Gatorade scientists on its the International Journal of Sports journals belong to organisations that have long editorial board. Medicine and Medicine and relationships with Gatorade (box). Several other prominent Science in Sports and Exercise. These links between sports medicine jour- Gatorade scientists sit on the To date, Asker has served as a board of the Journal of Sports reviewer for 35 different scientific nals and the sports drinks industry may help to Science. Mark Hargreaves, journals.”53 He is one of the main explain a characteristic of the sports drinks litera- professor of exercise physiology authors of research papers GSK ture that is familiar to those who have analysed and metabolism at Melbourne gave the BMJ to demonstrate the 9 drug trials over the past 30 years—the relative (or

LYNNE CAMERON/PALYNNE ARCHIVE/PA IMAGES University and a member of the effectiveness of its sports drinks. almost complete) absence of negative studies.

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WHAT THE RESEARCH FOUND The BMJ’s asked manufacturers to supply details of the studies underpinning sports Biological outcomes do not necessarily correlate with improved claims. Only one manufacturer, GSK, provided a comprehensive list of the trials performance—Reductions in use of muscle glycogen, for example, used to underpin its product claims for Lucozade—a carbohydrate-containing sports did not correlate with improved athletic performance. Physiological drink.45 Other manufacturers of leading sports drinks did not and in the absence of outcomes such as maximal oxygen consumption have also been systematic reviews we surmise that the methodological issues raised apply to all shown to be poor predictors of performance, even among elite athletes other sports drinks. Carl Heneghan, Rafael Perera, David Nunan, Kamal Mahtani, Inappropriate use of relative measures inflates the outcome and can and Peter Gill set out to appraise the evidence and found a series of problems with easily mislead—One study inflated the relative effect of carbohydrate the studies (see online for full article).9 drinks from 3% to 33% by excluding from the analysis the 75 minutes Small sample sizes limit the applicability of results—Only one of the 106 studies —in of exercise both groups undertook before an exhaustion test 257 marathon runners—exceeded the acceptable target for a small study of 100 participants per group. The next largest had 52 participants and the median sample Studies that lack blinding are likely to be false—Studies that used size was nine. Thus the results cannot be generalised beyond people with the study plain water as the control found positive effects whereas those that group characteristics used taste matched placebos didn’t Poor quality surrogate outcomes undermine the validity—Many studies used time Manipulation of nutrition in the run-in phase significantly affects FOODALANKING/ALAMY to exhaustion or other outcomes that are not directly relevant to performance in real subsequent outcomes—Many studies seemingly starve participants the life events night before and on the morning of the research study Poorly designed research offers little to instil confidence in product claims—Most Changes in environmental factors lead to wide variation in outcomes—Although studies (76%) were low in quality because of a lack of allocation concealment and dilute carbohydrate drinks may have some benefit in heat, studies found no effect in blinding, and often the findings contrasted with each other. The studies often had cold environments. No plausible reason given for benefits substantial problems because of use of different protocols, temperatures, work There was no substantial evidence to suggest that liquid is any better than solid intensities, and outcomes carbohydrate intake and there were no studies in children. Given the high sugar Data dredging leads to spurious statistical results—Studies often failed to define content and the propensity to dental erosions children should be discouraged from outcome measures before the study, leaving open the possibility of numerous using sports drinks. Through our analysis, we have come to one conclusion: people analyses and increasing the risk of finding a positive result by chance. should develop their own strategies for carbohydrate intake largely by trial and error.

Several people have told the BMJ how diffi- UK Sport, a quango accountable to the UK’s A recent campaign against the UK government cult it is to publish studies that question the role Department for Culture, Media and Sport, has levying value added tax on “sports nutrition of hydration. Paul Laursen is one of them. “[A also entered into a “research and development drinks” by UK Sports Specialist Nutrition Alliance negative study] gets rejected by reviewers and the partnership” with GSK. This is “to investigate the also shows how sport products are now thought editors for really spurious reasons—particularly role that nutrition has in improving athletic per- of as essential. “You complain about obesity then when you consider what does get published. It’s formance through the training process.” They too charge us to live a healthy lifestyle!” says one sig- a frustrating experience and it makes you wonder turned down the FOI requests for study protocols, natory. “Why penalise individuals for choosing if it’s a case of money winning out.” calling them “commercial in confidence.” to use products designed to maintain health and In response to concerns that drug companies vitality which ultimately help reduce the burden were burying negative studies or those that dem- Links to obesity on the already stretched and under resourced onstrated harm, the US government implemented As sports drinks rise in popularity among chil- NHS. We’re sitting on a diabetes and obesity time the FDA Amendment Act. This stipulated that pro- dren, there is concern their consumption is bomb,” says another. spective studies had to be registered on a publicly contributing to obesity levels. A 500 mL bottle This is why New York City’s mayor, Michael accessible database. However, this has not caught of Powerade Ion4 contains 19.6 g of sugar, and Bloomberg, has proposed a ban on supersized on in nutrition. the same sized bottles of Lucozade Sport and bottles of soft drinks, including sports drinks. As When the BMJ asked companies if they had any Gatorade Perform contain 17.5 g (32 g carbo- one marketing pundit put it, drinking a sports knowledge of negative trials—where sports drinks hydrates) and 30 g respectively (a teaspoon of drink “may be a way for consumers to convince have not shown improvement in outcomes—Coca- sugar weighs about 4 g). themselves that they are looking after the bodies Cola responded that it didn’t. “We would suggest A report in June 2012 by the US philanthropic without having to break out into a sweat.”39 you direct this question to an active researcher in organisation, the Robert Wood Johnson Foun- Far from sports drinks turning casual runners the field,” they said. But finding out what studies dation, says that “the increased consumption into Olympic athletes, Noakes suggests: “If they are being conducted isn’t easy. of sports drinks in recent years is of growing avoided the sports drink they would get thinner The BMJ turned to Loughborough Univer- concern for parents, health professionals, and and run faster.” sity, which will form one of the UK’s main hubs public health advocates.”47 Deborah Cohen investigations editor, BMJ, London directing research into sport and exercise as part Coca-Cola denies that the drinks are a prob- [email protected] of delivering the Olympic legacy. The univer- lem. “No one single food or drink alone is Competing interests: None declared Provenance and peer review: Commissioned; externally peer sity receives funding from Gatorade. Using the responsible for people being overweight or reviewed. F­reedom of Information (FOI) Act, the BMJ asked obese. All foods and soft drinks can have a place References are in the version on bmj.com. for the university’s contract with Gatorade and for in a sensible, balanced diet, as long as over time Cite this as: BMJ 2012;345:e4737 the protocols of studies conducted on humans. you do not take in more calories than you burn,” The request was turned down under a commercial it said. Related articles interests exemption. A subsequent letter said they However, endorsement by athletes and claims ̻̻Mythbusting sports and exercise products by didn’t have any studies under way, yet declined to of hydration benefits have meant that sports Carl Heneghan, Dan Lasserson, Jeremy Howick, say what they receive funding for. drinks have shrugged off any unhealthy associa- Peter Gill, Braden O’Neill, Miriam Thacke and “The public interest in maintaining the exemp- tions. An analysis by Yale University found that Matthew Thompson (BMJ 2012;345:e4848) tion outweighs the public interest in disclosing the over a quarter of American parents believe that ̻̻The evidence underpinning sports performance information,” the FOI officer said. sports drinks are healthy for children.48 products (BMJ Open 2012;2:e001702)

BMJ | 21 JULY 2012 | VOLUME 345 25 SPORTS DRINKS Food regulators must up their game Matthew Thompson, Carl Heneghan, and Deborah Cohen find worrying deficiencies in the evidence used to support the health claims made for sports drinks

n 2006, the European Union adopted legis- health, we set out to assess the scientific evidence between consumption of the food and claimed lation to assess health and nutrition claims and the scientific rigour of EFSA’s methods. We effect.” This seems an odd way of assessing the related to foods.1 This aims to ensure that found a major discrepancy between what they set balance of beneficial and harmful effects of an “claims made on food labelling and adver- out to do, and what they actually did. intervention (in this case sports drinks). tising regarding nutrition and health are Methods to assess the effectiveness of interven- We asked EFSA to confirm whether this was Imeaningful and accurate, and can thereby help tions (or more correctly, methods that assess the really its process and received this reply: “It’s very consumers in making healthy diet choices.” balance between beneficial and harmful effects) straight forward in fact: an applicant has to sub- From the end of 2012, all claims used to market have been established for several decades.5 6 mit all the research and data they think will prove and advertise a product will need to be approved. These methods of systematic review (or compar- that their claim is true. EFSA then reviews what- The body responsible for evaluating the scien- ative effectiveness) are used by regulatory and ever has been submitted to support the validity of tific basis of health claims is the European Food professional organisations, guideline groups, that claim, if EFSA finds that the research and sci- Safety Authority (EFSA). Their remit includes and government bodies worldwide to assess entific data submitted prove that there is a cause health claims related to the “roles of nutrients or drugs and medical devices or interventions such and effect relation between the product and the substances in growth, development or functions as diet, exercise, and counselling. However, the claim the evaluation is positive, if not, negative.” of the body, psychological or behavioural func- methods used by EFSA to assess the “nature and tions, or slimming or weight control.”2 quality of the totality of the evidence,” do not Our assessment of the evidence After the legislation was passed, individual measure up to these transparent and reproduc- We identified all references the EFSA panel cited member states supplied the European Commis- ible methods (table 2). for the two claims approved for sports drinks.4 sion with a list of over 44 000 health claims. After Firstly, EFSA asked manufacturers of sports One author (MT) then examined the titles and, duplicate or overlapping claims were removed, drinks to supply evidence for effectiveness of their where appropriate, abstracts of all the references these were narrowed down to a final list of 4637 own products. This presents a risk that manufac- to identify scientific trials. For the scientific trials claims; EFSA has evaluated 2758 of them and has turers will selectively present studies that report MT and CH then independently examined full text published scientific opinions on 341.1 products in a positive light. A better way would articles and extracted data on study type, study EFSA uses five panels to evaluate the claims, have been to ask for systematic reviews that quality (using randomisation, allocation conceal- one of which is the panel on dietetic products, detailed their search and appraisal methods, ment, intention to treat, and blinding) to catego- nutrition, and allergies (NDA).3 Scientific evalu- including studies with negative outcomes and rise studies as high, moderate, or low quality. We ations “should be scientifically substantiated” by unpublished studies. In the absence of systematic then assessed the relevance of each article to the “taking into account the totality of the available review evidence, a more comprehensive search claim for which it is cited and whether the out- scientific data, and by weighing the evidence,” in for primary studies should be used. come reported included a direct effect on sport- addition to reviewing the quality of the evidence. Secondly, EFSA did not seem to have any cri- ing performance (such as time to complete a race Evaluations are expected to show: teria to decide what types of scientific evidence or time trial). We also extracted details of study • The claimed effect of the food is beneficial for to accept, particularly in relation to study type or participants and calculated summary statistics human health quality. Submissions included not only scientific for age, sex, and type of athlete. • A cause and effect relation between studies, but also book chapters, opinion articles, consumption of the food and claimed effect and non-systematic review articles. Maintenance of endurance (such as strength, consistency, specificity, Thirdly, even for the scientific studies EFSA EFSA listed 54 references related to the claim of dose-response, and biological plausibility) received, we were unable to track down the meth- maintaining endurance performance, of which • The quantity of the food and pattern of ods they used to assess quality. This could mean, only 26 were scientific studies (table 3 online). We consumption required to produce the effect for example, low quality studies were given the were able to obtain full text papers for 25 of the • The populations in which the evidence was same “weight” as higher quality studies, poten- studies and the abstract for the other. The studies obtained are representative of the target tially biasing results. Finally, when assessing a included a total of 359 participants. Most (19/26) population for which the claim is intended. 2 body of evidence it is important to present the were poor quality. Participants were predomi- Using this process, the NDA panel assessed data extracted from each of the studies, so that nantly men (89%), endurance trained (73%), and scientific evidence related to three claims for car- the methods of analysis (including meta-analy- aged 20-30 years (65%). Of the 26 studies, only bohydrate-electrolyte solutions (sports drinks). sis where appropriate) are transparent and can 12 used an outcome that was related to improved They published their scientific opinion in June potentially be reproduced by others. Although sporting performance (running capacity, sprint- 2011 (table 1).4 EFSA did helpfully publish a list of all the refer- ing performance, tennis playing performance, ences it used to make its assessment, 4 it did not etc), of which only one measured performance How valid are EFSA’s methods? specify the process for analysing the evidence, in a race setting—a randomised controlled trial Given the importance of these claims for market- suggesting that it used an ad hoc process. of 98 marathon runners (which found no signifi- ing of sports drinks in Europe (for both consumers Finally, EFSA states that its approach was an cant effect of sports drink compared with water and manufacturers) and the potential effect on attempt to prove a “cause and effect relationship on marathon time).

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Table 1 | Claimed effects of sports drinks and EFSA panel conclusions about scientific evidence4 or older ­people, or only to those per- Claimed effect Target population Panel conclusions Reduction in perceived exertion or effort Active people who are A cause and effect relation has not been forming endurance during exercise (eg, delayed fatigue, exercising established exercise, which is the increased endurance performance) population for whom Enhancement of water absorption Active people doing endurance A cause and effect relation has been established during exercise (eg, better or/faster exercise between the consumption of carbohydrate- EFSA approved this claim. fluid delivery, rehydration, hydration, electrolyte solutions and enhancement of water Although many of the references cited by EFSA electrolyte balance/rehydration) absorption during exercise were review articles, none of them fitted the crite- Maintenance of endurance performance Active people doing endurance A cause and effect relation has been established ria for systematic reviews—most were consensus (eg, increased endurance capacity, exercise between the consumption of carbohydrate- endurance in heat) electrolyte solutions and maintenance of statements or clinical reviews. Moreover, EFSA endurance performance did not seem to have a robust process to assess the validity of systematic reviews. For exam- Table 2 | Comparison between accepted methods for assessing a body of evidence compared with what ple, one of the prominent reports EFSA cites in EFSA panel did to assess sports drinks support of these claims is a 1991 report of the Potential effects on internal and S­cientific Committee on Food. 8 The section of Accepted steps What EFSA panel did external validity Comprehensive and structured search Relied on manufacturers to supply Serious risk of selection bias for positive this document that reviews sports drinks (page of multiple electronic databases (or evidence for effectiveness studies or reports 21), refers to five references, two of which seem to trial registries) for published (and be n­on-systematic reviews, two are books or book unpublished) scientific studies ch­apters, and one a trial of eight men. Defined inclusion and exclusion criteria Apparently no defined inclusion and Included not only scientific studies, but for deciding which types of studies are exclusion criteria, particularly in relation also book chapters, opinion articles, and eligible to study type, study quality, or outcomes non-systematic reviews What should EFSA do now? of interest It will be up to individual countries to decide Assess the quality of included studies Did not assess quality Cannot take quality into account when interpreting findings how to implement the claims permitted by EFSA. Summarise or analyse the included Published a list of all the references they The process for analysing the body However, claims approved by EFSA will carry studies, using meta-analysis where used to make assessment of evidence identified is not specified considerable weight and be valuable to manu- appropriate and suggests that an ad hoc process or consensus process was used facturers. There is a risk that claims approved by EFSA will be used to market sports drinks to Enhanced water absorption during exercise positive outcomes, but very few of the studies had people for whom the evidence does not apply. EFSA listed 108 studies related to water absorp- equivocal or negative outcomes. Given that the Moreover, public organisations that monitor tion during exercise, of which only 22 were scientific evidence submitted by just one manu- advertisements for accuracy, such as the Adver- s­cientific studies, most of which (17/22) were facturer (GSK) exceeds that cited by EFSA,7 we tising Standards Authority in the UK, will simply poor quality (table 3 online). The studies included suspect the studies used by EFSA form only part defer to published EFSA opinions when fielding a total of 298 participants, of whom three quar- of the available data on these products. complaints about adverts, rather than looking ters (74%) were men; two thirds (67%) of the Secondly, many of the studies had methodo- at scientific evidence themselves. There should studies included people in their 20s (only three logical limitations, such as lack of blinding and be a process in place to challenge EFSA’s deci- included people older than 30 years). Most stud- concealment of allocation, use of laboratory sions on claims (both those upheld and those ies were carried out on either general populations rather than performance measures, and unre- rejected). (eight) or regular athletes (seven) rather than alistic study protocols.7 EFSA’s assessment did The timeline (and presumably resources) endurance athletes or professionals. not comment on the availability and quality of that EFSA was given to examine the scientific Of the 22 studies, most (21) had outcomes the data. We did not attempt to summarise or evidence for the thousands of food claims sub- that seemed to be relevant to the claim of water meta-analyse the outcomes of the studies cited mitted to them was clearly insufficient, placing absorption during exercise, but only 16 used an by EFSA because it would have been impossible it under enormous pressure. Our observation outcome that was directly related to improve- to draw conclusions given the lack of detail on the of EFSA’s processes suggests that it needs to ment in sporting performance or recovery (such methods it used to identify the included studies. develop greater expertise in the methods of sys- as rehydration rates, running capacity, sprinting A third major concern is “representativeness tematic review—indeed, it has recently funded performance), none of which had an outcome to the target population,” another criterion used such in-house training. Improvements in skill that included performance in a race or event. by EFSA. For the claim that sports drinks improve and providing more time to assess new and endurance performance, the majority of par- appealed claims will facilitate a more scientific Limitations of the evidence ticipants in cited studies were young endurance and rigorous approach to assessing the scientific Putting aside our methodological concerns with athletes, and any evidence of benefit is therefore basis of food claims in Europe. EFSA’s process to assess the scientific validity only applicable to such people. EU countries Matthew Thompson senior clinical scientist of the claims related to sports drinks, the body should therefore ensure that use of this claim in [email protected] of evidence it cites in permitting the two claims labelling or marketing of products makes it clear Carl Heneghan reader in evidence based medicine, seems to have serious limitations. that the effect is limited to those participating in Department of Primary Care Health Sciences, University of Oxford, Oxford OX2 6GG, UK Firstly, the trials cited are small (median 9-10 prolonged endurance exercise. The studies used Deborah Cohen investigations editor, BMJ, London people), including a total of only a few hundred to support the claim that sports drinks enhance Competing interests: None declared. people—and not all of them used an outcome water absorption included a wider spectrum of Provenance and peer review: Commissioned; externally peer directly related to the claim. Only one study physically active people. Again most were men in reviewed. measured outcome in a race. We were not able their 20s, so it is difficult to know whether the find- References are in the version on bmj.com. to determine whether the studies were biased to ings (and the claims) apply to women, children, Cite this as: BMJ 2012;345:e4753

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COMMENTARY The role of hydration in health and exercise Water is the major constituent of the human body temperature during exercise is the exercise inten- and the total body water content is tightly regu- sity or metabolic rate; the greater the intensity, the lated. The goal is to ensure that the water content higher the temperature.1 of the cells and hence their size remains within a Humans can raise their body temperatures homeostatically regulated range. slightly more (adaptive heterothermy) when forced Humans evolved as long distance persistence to exercise without any or optimum fluid replace- hunters on the arid savannahs of south and east ment. The higher body temperature increases the Africa. We inherited the capacity to regulate our gradient for heat loss by convection, thus reducing body temperatures during prolonged exercise in the need to increase sweat losses to maintain safe

dry heat despite quite large reductions in total HOFFMAN/GETTY IMAGES/FOTO24/LOANNA GALLO body temperatures and conserving water. body water—no other mammal has the equiva- Timothy Noakes: dehydration’s only symptom is lent capacity. thirst—the effect of which is to induce drinking Treatment of collapsed athletes Humans do not regulate fluid balance on a Clinicians often assume that athletes collapse after moment to moment basis. Because of our evo- correct the blood osmolality. This control ensures exercise because they are hypotensive (and hyper- lutionary history, we are delayed drinkers and that humans always drink just enough but not too thermic) as a result of dehydration. In fact, most correct the fluid deficits generated by exercise at, much. There is no intrinsic biological drive that have exercise associated postural hypotension, a for example, the next meal, when the electrolyte will cause overdrinking. Voluntary overdrinking form of vaso-vagal fainting that occurs in suscep- (principally sodium but also potassium) deficits causes blood osmolality to fall, which should tible individuals within seconds or minutes after are also corrected.1 As a result, there is no need inhibit thirst and reduce the pituitary release of exercise terminates.1 4 6 The treatment is recovery to completely replace any fluid deficit as it devel- antidiuretic hormone (ADH). ADH regulates water in the head down Trendelenberg position.7 ops either at rest or during exercise. Instead peo- reabsorption in the distal renal tubules and is one Clinical signs of dehydration are unreliable in ple optimise their hydration status by drinking of the most potent human hormones. Paradoxi- detecting substantial fluid loss in athletes com- according to the dictates of thirst. cally, athletes who develop exercise associated pleting endurance events.8 Athletes who finish Over the past 40 years humans have been hyponatraemic encephalopathy report persist- exercise with thirst are mildly dehydrated and misled—mainly by the marketing departments ent thirst and retain fluid, even though their blood need to eat and drink in order to replace their of companies selling sports drinks—to believe osmolality is falling; this suggests the presence of solute and fluid deficits.1 Athletes who complete that they need to drink to stay “ahead of thirst” the syndrome of inappropriate ADH secretion.1 2 exercise without thirst do not need any specific to be optimally hydrated. In fact, relatively small treatment. Any presenting complaints in athletes increases in total body water can be fatal. A 2% Dehydration in a sports setting who do not report that they are also thirsty cannot increase in total body water produces generalised Dehydration is not a medical illness.1 Correctly be caused by dehydration. oedema that can impair athletic and mental per- used, the term refers to a reduction in total body By contrast, the symptoms and signs of over- formance; greater levels of overhydration result in water content. Thus dehydration’s only symptom hydration are unmistakable. The athlete shows hyponatraemic encephalopathy— severe cerebral is thirst—the effect of which is to induce drinking.3 marked changes in cerebral function, from mild oedema that produces confusion, seizures, coma, There is barely any risk that dehydration can occur withdrawal, to confusion, seizures, and coma. and ultimately death from respiratory arrest.1 in healthy athletes competing in a modern endur- The diagnosis is confirmed by measuring blood ance event in which ample fluid is available.1 Only sodium concentration; the lower the value, the Why we feel thirsty during exercise when the total body water is reduced by about more severe the fluid overload.2 9 Sweat is a relatively dilute plasma secretion con- 15%—as occurs in those lost in the desert with- Overhydration is treated by absolute fluid taining more water than electrolytes. As a result out water for more than 48 hours—is voluntary restriction and bolus 3-5% hypertonic saline infu- sweating increases blood sodium concentrations motor activity completely inhibited, resulting in sions for those with confusion or coma.10 This rap- and osmolality. These increases are sensed by paralysis.1 idly reverses the mental confusion in people with receptors in the hypothalamus, which respond Confusion arose when the erroneous belief mild hyponatraemia11 and produces rapid diuresis by producing hormonal and behavioural changes that all athletes who collapse after exercise are in those with exercise associated hyponatraemic designed to maintain the osmolality within the suffering from a dehydration induced heat ill- encephalopathy. If brain swelling is so advanced homeostatically regulated range. ness was promoted as part of the false “science of that there is a high risk of respiratory arrest or cere­ Hormonal changes increase renal sodium and hydration.”1 This dictated that people collapsing bellar coning, diuretics and intravenous mannitol water conservation; reflex stimulation of the ante- needed to drink more fluids during exercise and infusions may be needed.12 rior cingulate gyrus produces the conscious sensa- immediate resuscitation with large volumes of T D Noakes Discovery Health chair of exercise and sports tion of thirst that drives water seeking behaviour. intravenous fluids. science, Department of Human Biology, University of As the sensation of thirst rises, exercise perform- However, athletes who collapse are neither hot- Cape Town and Sports Science Institute of South Africa, Newlands 7700, South Africa ance becomes progressively impaired—a useful ter nor more dehydrated than control runners who 1 4 [email protected] control since it reduces the exercise intensity and complete the same races without collapsing. Competing interests: None declared. hence the possibility of continuing large water loss Sporadic cases of heatstroke are also not caused Provenance and peer review: Commissioned; externally peer through sweating. by dehydration.1 5 Hydration influences regula- reviewed. The sensation of thirst ceases when sufficient tion of body temperature in competitive athletes References are in the version on bmj.com. fluid and solute (electrolyte) have been ingested to only indirectly. The key determinant of the body Cite this as: BMJ 2012;344:e4171

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