{"id":1275,"date":"2011-05-12T23:39:14","date_gmt":"2011-05-12T22:39:14","guid":{"rendered":"http:\/\/stg-blogs.bmj.com\/bjsm\/?p=1275"},"modified":"2011-05-12T23:42:18","modified_gmt":"2011-05-12T22:42:18","slug":"research-review-by-dr-evan-lloyd-are-the-recommendations-for-fluid-intake-in-humans-valid","status":"publish","type":"post","link":"https:\/\/stg-blogs.bmj.com\/bjsm\/2011\/05\/12\/research-review-by-dr-evan-lloyd-are-the-recommendations-for-fluid-intake-in-humans-valid\/","title":{"rendered":"Research Review by Dr. Evan Lloyd: Are the recommendations for fluid intake in humans valid?"},"content":{"rendered":"

Guest Blog Author: Dr. Evan Loyd<\/em><\/p>\n

Abstract: <\/strong>The current consensus recommendations for fluid intake have been examined and found to be false or inapplicable in the situations for which they are recommended.\u00a0 The dangers to the people and the environment are detailed and the vested interests perpetuating these recommendations described.<\/p>\n

\"\"<\/p>\n

Introduction<\/strong><\/p>\n

Scientists studying fluid balance in humans have produced consensus recommendations for fluid intake needs for humans.\u00a0 Are these statements valid?<\/p>\n

<\/strong><\/p>\n

Consensus position 1.<\/strong><\/p>\n

Adult males need to drink 3.7l per day to remain healthy.<\/p>\n

Facts<\/strong><\/p>\n

In 1945, research showed that human beings lose about 2.5 l per day of fluid.\u00a0 The recommendation that \u201ca suitable allowance of water for adults is 2.5 l per day\u201d was concluded by the observation that \u201cMost of this quantity is contained in prepared foods\u201d\u00a0 [1].\u00a0 This last sentence has been generally ignored, and an article, written in a journal called American Fitness [2], stated that, according to \u201cmost authorities\u201d (unspecified) 8 glasses each of 8 fluid ounces (total 3.7l) of water per day is necessary for sedentary people.\u00a0 This excludes caffeinated drinks.\u00a0 The complete lack of evidence supporting this recommendation is exhaustively catalogued by Heinz Valtin in an invited review in the American Journal of Physiology [3].\u00a0 Despite this, Campbell [4] quotes the figure that Americans only drink 48 fl oz bottled water per day, and states that an adult male needs to consume 3.7 l (125 fl oz) total water daily to remain healthy.\u00a0 Infants, and those who are ill (a category including athletes [5]) do not meet their daily water needs by relying on thirst [4].\u00a0 However she also states that most healthy people meet their daily water needs when they let thirst be their guide [4], and that healthy people are able to quickly compensate for over or underhydration [4]. \u00a0 In view of these points why should people not rely on thirst for hydration, and are athletes not healthy people?<\/p>\n

In fact, man has evolved with kidneys which can conserve water by producing concentrated urine (reducing renal free water loss), and the osmotic threshold for the release of vasopressin (the enzyme which stimulates the kidneys to conserve fluid by concentrating the urine) is lower than that which stimulates thirst, which in turn is lower than the osmolality at which dehydration is considered to start [3].<\/p>\n

Conclusion<\/strong><\/p>\n

This consensus, based on a combination of no evidence and selective selection of research results, is therefore invalid.<\/p>\n

\n

Consensus position 2.<\/strong><\/p>\n

To maintain performance, athletes must drink during events.<\/p>\n

\"\"<\/p>\n

Facts<\/strong><\/p>\n

Laboratory experiments found that physical performance is markedly (10%) impaired by dehydration of -2% body weight, and therefore, contrary to previous recommendations, athletes should drink copiously during exercise [5].\u00a0 However if the rate of intake of hypotonic fluids (water) exceeds renal free water excretion, hyponatraemia is inevitable [6].\u00a0 Therefore when the consensus recommendation became universally applied, it led to cases of hyponatraemia, and some deaths [7]. \u00a0 Proponents of the consensus [5] ignore, or dismiss, the clinical observations [8] that in an ironman triathlon a weight (fluid) loss of 5.0 \u2013 10.7% of body weight did not impair endurance performance.\u00a0 In fact those losing most weight tended to have the fastest times.\u00a0 Nor were increases in core temperature related to decreases in body weight [8].<\/p>\n

The environment, and the physiological changes recorded in laboratory experiments, differ from those that occur in the \u2018field\u2019 situation [9,10].<\/p>\n

In a \u201chot\u201d laboratory, the only heat loss mechanisms are evaporation, plus some pendulum convective heat loss through limb movement.\u00a0 By contrast in the \u201chot\u201d field, there is air movement over the whole body.\u00a0 The increased convective cooling will produce more efficient evaporation of sweat, with a reduced requirement for sweat production. The limited convective cooling in the laboratory will result in a higher sweat rate than in the field, through increased need for evaporative heat loss, and also through greater wastage of sweat, with more liquid sweat running off the body.<\/p>\n

Because of time constraints inherent in laboratory studies, dehydration has to be induced rapidly prior to the exercise test.\u00a0 Fluid loss is induced by a variety of methods, including using a diuretic [11]. \u00a0 Of the fluid containing compartments in the body, intracellular, intercellular and intravascular, fluid can only be rapidly removed from the intravascular space.\u00a0 The laboratory subject therefore starts the exercise with a relative hypovolaemia rather than general dehydration. When the exercise starts, the reduced available circulating volume results in impairment of the mechanism for heat loss from the skin through having insufficient fluid to fill all the available skin capillaries. The core temperature will therefore rise faster than it would with a full circulating volume.\u00a0 The pre-induced dehydration\/hypovolaemia means that the heart will have to work harder than normal to provide circulation to the working muscles, and to the skin. \u00a0 The cardiac output will reach maximum at a lower level of exercise than with a normal blood volume.<\/p>\n

In the field, the athlete starts with a full circulating volume, with possibly some extra fluid.\u00a0 As fluid is gradually lost from the circulation through sweating, and breathing, the exercise itself causes fluid transfer, first from the interstitial space into the intravascular space to replace the fluid loss [12], then, if fluid loss continues, fluid is transferred from inside the cells to the interstitial space [12]. Thus the endurance runner will finish the event with loss of fluid from the interstitial space, and possible slight dehydration of the cells, but with minimal depletion of the circulating fluid volume. There will therefore be adequate circulating volume to maintain a full circulation in the skin capillaries, with high skin temperature and maximum heat loss. \u00a0 The heart would be under less stress.<\/p>\n

Also, in any sport in the field, the athlete can use his brain, consciously or unconsciously, and adjust the speed and intensity of effort depending on \u201cgame strategy\u201d, needs of the event [13-16], core temperature or heart rate.\u00a0 In the laboratory the exercise schedule is pre-determined [13,16].<\/p>\n

The proponents of the consensus also seem to ignore the fact that extreme endurance exercise produces an antidiuretic status, through significant non-osmoregulated AVP (posterior pituitary hormone vasopressin) release, and therefore reduced renal free water excretion [6].\u00a0 There is therefore less need for water intake.<\/p>\n

The development of the world\u2019s first sports drink, and its rampant commercial success, required the development of physiological dogmas that are the opposite of man\u2019s (sic) evolutionary biological design.\u00a0 These include:<\/p>\n

Man is poorly adapted for exercising in the heat.<\/p>\n

Man must not develop any weight loss during exercise i.e. \u201czero dehydration\u201d rule [17].<\/p>\n

In fact, man evolved as a species able to run (hunt) for prolonged periods in the heat whilst maintaining a safe body temperature [18,19].\u00a0 Even today populations like the Kung San in Namibia, who continue \u201cpersistent\u201d hunts [20], have been tracked as they ran for 6 hours in temperatures between 40-45 o<\/sup>C while they drank little – less than 1 litre [20].<\/p>\n

Conclusion<\/strong><\/p>\n

The conclusions reached as a result of the laboratory studies are valid as claimed.\u00a0 However, the laboratory results are not valid when applied to the situation in the field. Athletes need to be advised to follow their thirst as they run rather than simply taking on fluid [6].<\/p>\n

A whole supplement of the Journal of the American College of Nutrition [21] was devoted to studies, which showed that even mild \u201cunderhydration\u201d had a deleterious effect on virtually every function of the human body and brain.\u00a0 Are the results clinically as well as statistically significant, and are the subjects dehydrated or hypovolaemic?<\/p>\n

The aim seems to be to establish the myth that, for health and performance, man must remain hydrated at all times.\u00a0 If this fact was true, man would be the only species on earth with this requirement!! In reality [3] man has evolved to be able to perform well during mild dehydration (sometimes over considerable time), following which healthy man will always rehydrate, provided there is time and available fluid.<\/p>\n

Vested Interests, <\/strong>Distortions <\/strong>and Manipulations<\/strong><\/p>\n

The drinks\/sports drinks manufacturers make huge profits from the sale of rehydration fluids, soft drinks and bottled water.\u00a0 (Bottled water, and tinned pet food, are the top two profit makers for supermarkets in the UK.)<\/p>\n

The manufacturers keep their products in the limelight by sponsoring prestigious sporting events e.g. Coca Cola and the Olympic Games.<\/p>\n

Many of the proponent scientists are given salaries &\/or research funding, by the drinks companies, and\/or work in laboratories funded by the drinks companies.\u00a0 This makes it difficult for the scientists who are the proponents of the consensus to change their opinions easily.<\/p>\n

These scientists issue consensus statements [22], though the only people in the group are those with a history of supporting their particular position.<\/p>\n

The proponents are insisting that laboratory studies can be projected straight into the field\/clinical situation.<\/p>\n

The overwhelming evidence of the danger of\u00a0 hyponatraemia following overdrinking,\u00a0 induced the American College of Sports Medicine (ACSM) to reduce its guidelines on the volumes of\u00a0 water that should be drunk during exercise.\tDespite this, \u201cscientifically based\u201d advice in fitness magazines, websites and advertisements continues to give advice to drink far in excess of the official ACSM guidelines<\/a>.\u00a0 There is also international variation on website advice given by the same company \u2013 many websites still state \u201cyou can never drink enough\u201d [23].<\/p>\n

Murray [24] attacked opinions dissenting from the \u2018established\u2019 dogma on fluid intake during exercise, in a response titled \u201cManufactured arguments: turning consensus into controversy does not advance science.\u201d\u00a0 Surely that is precisely how science does advance!! Without it, we would still believe the world was flat.\u00a0 This is an example of \u201ccontrarianism\u201d in modern scientific debate [25].<\/p>\n

Results<\/strong><\/p>\n

1. There is a fear about not drinking enough (the worried well), and it is very common to see people carrying bottles of water wherever they go, and drinking at frequent intervals.<\/p>\n

2. Vast amounts of money is wasted buying bottled water.<\/p>\n

Bottled water in USA is no purer than tap water, and both may contain bacteria or carcinogens [3].\u00a0 Therefore high water intake, bottled or tap, will increase one\u2019s exposure to pollutants [3].<\/p>\n

3. Endurance athletes, people using ecstasy, and even a high school football player have died from hyponatraemia [7,17,23] through following the consensus advice.<\/p>\n

Hyponatraemia is causing problems in women in labour who drink lots of water [26].\u00a0 Delivery becomes more difficult and is significantly linked with instrumental delivery and emergency Caesarean section for failure to progress.<\/p>\n

4.\u00a0 The insistence, on the need for all athletes to drink frequently, can impair performance in team competitions where endurance and sweating is not a problem e.g. curling.\u00a0 Fluid overload will necessitate the athlete temporarily interrupting participation because of the need to empty the bladder [Personal Observation at Word Junior Curling Championship 2009], leaving the team weakened, and the prior discomfort of an overfull bladder may have a deleterious effect by disturbing concentration.<\/p>\n

5.\u00a0 Oestrogen-mimicking chemicals can leach into drinking water, and other beverages, from bottles made from certain plastics [27].<\/p>\n

6. There is a massive environmental impact from the energy requirements in the manufacture of the plastic bottles, and the contents, which are often only water.\u00a0 The disposal of the plastic bottles uses up landfill sites, and often disfigures beautifully scenic countryside.\u00a0 (Metal and glass containers cause the same problems, plus, when broken or distorted, they can cause serious injuries.)\u00a0 Even if disposed of at sea the effects are harmful.\u00a0 Plastic bottles litter our beaches, and can last for 1000 years.\u00a0 Plastic litter can be mistaken for food by 170 species of marine wildlife resulting in death through starvation, poisoning or stomach blockage.\u00a0 Plastic is eventually ground down into granules which accumulate in the marine environment and release toxic chemicals into the sea water from where they enter the food chain [28,29].<\/p>\n

Postscript.<\/strong><\/p>\n

\u201cConsensus\u201d<\/strong> \u2013 agreement in opinion (Chambers 20th<\/sup> Century Dictionary).\u00a0 This does not require that the opinion is true, or factually correct.\u00a0 \u201cConsensus\u201d must match all the known facts, and be open to change as new facts appear.\u00a0 Problems arise if the consensus, despite strong evidence to the contrary, is strongly supported by a group with power, which may be political &\/or financial.<\/p>\n

Competing interest:<\/strong><\/p>\n

I declare that I have had no support from any organisation for the submitted work; no\u00a0financial relationships with any organisations that might have an interest in the previous\u00a0three years; no other relationships or activities that could appear to have influenced the\u00a0submitted work.<\/p>\n

References<\/strong><\/p>\n

<\/strong><\/p>\n

1.\u00a0 Food and Nutrition Board, National Academy of Science.\u00a0 Recommended Dietary Allowances, revised 1945.\u00a0 National Research Council, Reprint and Circular Series, No 122: 1945; p 3-48.<\/p>\n

2.\u00a0 Hines D.\u00a0 The Power of H2<\/sub>O.\u00a0 American Fitness. 2001; 19: 23-25.<\/p>\n

3.\u00a0 Valtin H.\u00a0 \u201cDrink at least eight glasses of water a day.\u201d\u00a0 Really? Is there scientific evidence for \u201c8×8\u201d?\u00a0 American Journal of Physiology, Regulatory, Integrative and Comparative Physiology.\u00a0 2002;283: R993-R1004.<\/p>\n

4.\u00a0 Campbell S M. Hydration needs throughout the lifespan. J Am Coll Nutr\u00a0 <\/em>2007; 26 (5): 585S-587S<\/p>\n

5.\u00a0 Murray B.\u00a0 Hydration and physical performance. J Am Coll Nutr 2007; 26 (5): 542S-548S.<\/p>\n

6. Ball SG.\u00a0 Hyponatraemia.\u00a0 J R Coll Physicians Edinb 2010; 40:240-245.<\/p>\n

7.\u00a0 Noakes T, Speedy D.\u00a0 Case proven: exercise associated hyponatraemia is due to overdrinking. So why did it take 20 years before the original evidence was accepted? Br J Sports Med\u00a0 2006; 40: 567\u2013572<\/p>\n

8.\u00a0 Sharwood K A, Collins M, Goedecke J H, et al.\u00a0 Weight changes, medical complications, and performance during an Ironman triathlon, Br J Sports Med\u00a0 2004; 38: 718\u2013724.<\/p>\n

9.\u00a0 Grant S, Lloyd E.\u00a0 Training and Performance in Difficult Environments. A guide for competitive athletes.\u00a0 The Crowood Press Ltd, Marlborough, Wiltshire. (2006) ISBN 1-86126-881-5.<\/p>\n

10.\u00a0 Lloyd E.\u00a0 Hyponatraemia and dehydration. Calming the controversy?\u00a0 Br J Sports Med.\u00a0 Electronic responses to ref 45.\u00a0 19\/02\/2007.<\/p>\n

11.\u00a0 Armstrong L E, Costill D L, Fink, W J.\u00a0 Influence of diuretic-induced dehydration on competitive running performance, Med Sci and Sport and Exercise\u00a0 17; 456\u2013461, 1985.<\/p>\n

12. Tappan D V, Jacey, M J, Heyder E, Gray P H.\u00a0 Blood volume responses in partially dehydrated subjects working in the cold, Aviat Sp and Environ Med \u00a0 1984; 55: 296\u2013301<\/p>\n

13.\u00a0 Noakes TD. \u00a0 Testing for maximum oxygen consumption has produced a brainless model of human exercise performance. Br J Sports Med \u00a0 2008; 42: 551-5<\/p>\n

14.\u00a0 St Clair Gibson A, Noakes TD.\u00a0 Evidence for complex system integration and dynamic neural regulation of skeletal muscle recruitment during exercise in humans.\u00a0 Br J Sports Med\u00a0 2004; 38(6): 797-806.<\/p>\n

15.\u00a0 Noakes TD, St Clair Gibson A, Lambert EV.\u00a0 From catastrophe to complexity: a novel model of integrative central neural regulation of effort and fatigue during exercise in humans: summary and conclusions.\u00a0 Br J Sports Med.\u00a0 2005; 39: 120-4.<\/p>\n

16.\u00a0 Morante SM, Brotherhood JR.\u00a0 Thermoregulatory responses during competitive singles tennis.\u00a0 Br J Sports Med\u00a0 2008; 42; 736-41.<\/p>\n

17.\u00a0 Noakes TD.\u00a0 Address to Fellows and Members of the Faculty of Sport and Exercise Medicine (UK). \u00a0 2008<\/p>\n

18. Carrier DR.\u00a0 The energetic paradox of human running and hominid development.\u00a0 Current Anthropology\u00a0 1984;25940:483-95.<\/p>\n

19\u00a0 Bramble DM, Lieberman DE.\u00a0 Endurance running and the evolution of Homo.\u00a0 Nature\u00a0 2004;432(7015):345-52.<\/p>\n

20.\u00a0 Liebenberg L.\u00a0 Persistence hunting by modern hunter-gatherers.\u00a0 Current Anthropology\u00a0 2006;47(6):1017-25.<\/p>\n

21. Journal of the American College of Nutrition 2007; 26, Special supplement<\/p>\n

22. Armstrong LE, Buyckx M, Campbell S et al.\u00a0 Scientific consensus statement regarding the importance of hydration and total water intake for health and disease. J Amer Coll of\u00a0 Nutrition \u00a0 2007; 26: 531S-2S.<\/p>\n

23.\u00a0 Beltrami FG, Hew-Butler T, Noakes TD.\u00a0 Drinking policies and exercise-associated hyponatraemia: is anyone still promoting overdrinking? Br J Sports Med 2008; 42; 496-501.<\/p>\n

24.\u00a0 Murray B. <\/strong>Manufactured arguments: turning consensus into controversy does not advance science.\u00a0 Br J Sports Med\u00a0 2007; 41:106-107.<\/p>\n

25.\u00a0 Noakes TD, Speedy DB.\u00a0 Lobbyists for the sports drink industry: an example of \u201ccontrarianism \u201c in modern scientific debate.\u00a0 Br J Sports Med\u00a0 2007;41(2):1107-9.<\/p>\n

26. Moen V, Brudin L, Rundgren M, et al.\u00a0 Hyponatremia complicating labour \u2013 rare or unrecognised?\u00a0 A prospective study.\u00a0 BJOG 2009;116:564-73.<\/p>\n

27.\u00a0 Mittelstaedt M.\u00a0 Estrogenic toxin found in widely used plastic.\u00a0 The Globe and Mail, 2009\u00a0 March 26pA9 Col1.<\/p>\n

28.\u00a0 Editorial.\u00a0 It\u2019s just litter but it will cost us the earth.\u00a0 Scotsman 2008 10 April p29<\/p>\n

29.\u00a0 Urquhart F.\u00a0 Plastic like this to blight our beaches for 1000 years. Scotsman 2008; 10 April pp 1&2.<\/p>\n

Have ideas to contribute to the discussion of hydration in sport? <\/span><\/strong><\/em>Please leave your comment below or email: <\/span><\/strong><\/em>karim.khan@ubc.ca<\/span><\/em><\/strong><\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

Guest Blog Author: Dr. Evan Loyd Abstract: The current consensus recommendations for fluid intake have been examined and found to be false or inapplicable in the situations for which they are recommended.\u00a0 The dangers to the people and the environment are detailed and the vested interests perpetuating these recommendations described. Introduction Scientists studying fluid balance […]<\/p>\n

Read More…<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[173,188,187,179],"tags":[],"class_list":["post-1275","post","type-post","status-publish","format-standard","hentry","category-debates","category-guest-posts","category-hot-topic","category-reviewing"],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/stg-blogs.bmj.com\/bjsm\/wp-json\/wp\/v2\/posts\/1275","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/stg-blogs.bmj.com\/bjsm\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/stg-blogs.bmj.com\/bjsm\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/stg-blogs.bmj.com\/bjsm\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/stg-blogs.bmj.com\/bjsm\/wp-json\/wp\/v2\/comments?post=1275"}],"version-history":[{"count":0,"href":"https:\/\/stg-blogs.bmj.com\/bjsm\/wp-json\/wp\/v2\/posts\/1275\/revisions"}],"wp:attachment":[{"href":"https:\/\/stg-blogs.bmj.com\/bjsm\/wp-json\/wp\/v2\/media?parent=1275"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/stg-blogs.bmj.com\/bjsm\/wp-json\/wp\/v2\/categories?post=1275"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/stg-blogs.bmj.com\/bjsm\/wp-json\/wp\/v2\/tags?post=1275"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}