Let's look beyond the marathon aspect in its over-specificity. The question asks for when was it recognised to drink water while exercising heavily would be advisable?
That means the scientific side has to be examined and not necessarily the practical application or even the commercial availability of specialised products, Brawndo-style.
This focus on water for performance began in Sweden during the 1930s, curiously as a by-product of analysing carbohydrate metabolism.
The development of nutritional beverages specifically geared towards improving athletic performance started with studies on carbohydrate and fat metabolism conducted in Sweden in the 1930s and continued into the late 1960s. The team of scientists led by Bjorn Ahlborg and Jonas Bergström studied the relationship among muscle glycogen storage, use, and resynthesis during prolonged exercise to exhaustion in a group of volunteers. The research by the Swedish team demonstrated a performance-enhancing role for carbohydrates during endurance exercise and showed that glycogen content and the long-term exercise capacity could be varied by instituting different diets after glycogen depletion.
Gustavo A. Galaz: "An Overview on the History of Sports Nutrition Beverages", Nutrition and Enhanced Sports Performance, Second Edition, p231, Elsevier, 2019.
The "exercise to exhaustion" is of course just a relative measure depnding on the tested individual and its fitness level.
This work continued
A slight sodium deficiency can impair athletic performance before any clinical signs of sodium lack are discernible. Therefore, during hot weather, adequate amounts of salt and water should be given to replace losses of these substances through the skin.
Theodore B. Van Itallie: "Nutrition and Athletic Performance", JAMA, November 17, 1956. (p 1126)
Molnar, G.W., Towbin, E.J., Gosselin, R.E., Brown, A.H. & Adolph, E.F.: "A comparative study of water, salt and heat exchanges of men in tropical and desert environments", American Journal of Hygiene 44, 411–433, 1946.
Adolph, A. & Associates: "Physiology of Man in the Desert". Wiley, New York, 1947.
Bass, D.E., Kleeman, C.R., Quinn, M., Henschel, A. & Hegnauer, A.H.: "Mechanisms of acclimatization to heat in man", Medicine 34, 323–380, 1955.
Buskirk, E.R., Iampietro, P.F. & Bass, D.E.: "Work performance after dehydration: effects of physical conditioning and heat acclimatization", Journal of Applied Physiology 12, 189–194, 1958.
Grande, F., Monagle, J.E., Buskirk, E.R. & Taylor, H.L.: "Body temperature responses to exercise in man on restricted food and water intake", Journal of Applied Physiology 14, 194–198, 1959
Senay, L.C. & Christensen, M.L.: "Cardiovascular and sweating responses to water ingestion during dehydration", Journal of Applied Physiology 20, 975– 979, 1965.
Moroff, S.V. & Bass, D.E.: "Effects of overhydration on man’s physiological responses to work in the heat", Journal of Applied Physiology 20, 267–270, 1965.
Strydom, N.B. & Holdsworth, D.L.: "The effects of different levels of water deficit on physiological responses during heat stress", Internationale Zeitschrift für Angewandte Physiologie 26, 95–102, 1968.
Cage, G., Wolfe, S., Thompson, R. & Gordon, R.: "Effects of water intake on composition of thermal sweat in normal human volunteers", Journal of Applied Physiology 29, 687–690, 1970.
American College of Sports Medicine: "Position statement on prevention of heat injuries during distance running", Medicine and Science in Sports and Exercise 7, vii–ix, American College of Sports Medicine, 1975.
It seems quite clear that it's been known for long in the medical literature that it's not really "water is essential for marathons", but that adequate hydration is really just one small angle to view a balanced scale.
Therefore, allow me a small link to an article that describes the current stae of trickle-down science, with a highlight on Exercise-associated hyponatraemia:
James M Winger et al.: "Beliefs about hydration and physiology drive drinking behaviours in runners", Br J Sports Med 2011; 45: 646–649. doi:10.1136/bjsm.2010.075275
And the belief angle is indeed crucial to understand why pre 1970s and especially in the very early years of the last cebtury the advice given out to runners looks very strange today to us.
Fundamental science was way advanced in its understandings compared to what applied and empirical sports science had to say about it.
The early advice was based on empiricism, but a purely observational one that was tainted by attitudes:
Contrary to popular theories and beliefs, distance runners predating 1970 were encouraged to drink as little as possible. Early studies of elite distance athletes showed the more successful athletes were the ones losing the most fluids of anyone in the race. These data concluded that a runner should not replenish the fluid lost during a race. To achieve even better results, it was suggested to have no fluid intake at all. In Tim Noakes book, Waterlogged, he talks about running a marathon in 1969 that had only water stop, at mile 20. As running became more popular, scientists conducted further research and came to some different conclusions...
Health risks of dehydration became more apparent in research after 1970, leading scientists to recommend that distance athletes drink during exercise. Frequent drinking was encouraged and promoted as the dangers of dehydration became even more evident as people suffered through injuries and even succumbed to death during races. Sports drink companies, such as Gatorade, were founded during this time period and began running advertisements in which professional athletes endorsed their product and talked about how hydration and sports drinks would lead to increased performance. (src)
Going back to the early days of marathon running, it was thought that the consumption of most fluids during long races like a marathon was not needed and even detrimental. Why? Because runners were studied and it was found that at the end of the race, the winners or top finishers lost the most body weight. The logic was that the best runners lost the most water weight, therefore losing fluids was necessary to maximize performance and hydration should not occur. The top runners were the most dehydrated, so dehydration is good! This line of thinking is used often, even to this day (i.e. The Kenyans do X, so X should be done…). This should be a cautionary tale to doing something just because the fastest guys do it.
So early in the history of hydration we have a policy of no drinking. What happens next?
With the rise of mass participation running, an increased awareness of illnesses associated with dehydration and the ability to measure hydration status very easily and quickly, we overreacted. The norm went from drinking nothing during exercise to trying to replace all of your fluid loss during exercise by drinking water or sports drinks. The common advice of measuring yourself before and after exercise to calculate hydration needs reached mantra status with coaches, nutritionist, trainers, and the common exerciser.
According to a nice summary by Mundel (BJSM-2011), one reason for this overreaction was the design of studies which measured the effect of drinking on tests at fixed intensities which essentially found how long you could go, and not how fast you can go over a fixed distance, which is what we do in the real world.
As mentioned above, the other reason is that heat exhaustion and similar illness became more prevalent with the rise of mass participation. The thinking was simple, extreme dehydration caused some problems and helped contribute to heat exhaustions, therefore if we eliminate dehydration heat exhaustion and similar illnesses would be eliminated. The problem with this thinking is similar to the “no drinking” logic. Just because a lot of dehydration is bad, doesn’t mean we need to eliminate all of it. It’s only bad if it gets to a dangerous point outside of the norms. Until it gets to that point, which is hard to do unless you force yourself not to consume any fluids (which is what was occurring in the previous period), you are fine.
You see this “all or none” thinking in a myriad of different places. Some obvious examples through history are: free radicals, carbohydrates, fat, lactate, etc. Just because a lot is bad, doesn’t mean a little is.
The history of Hydration : A lesson in the scientific method and the Hype cycle.
That resonates nicely with the mentioned above Toby Mündel; "To drink or not to drink? Explaining “contradictory findings” in fluid replacement and exercise performance: evidence from a more valid model for real-life competition", British Journal of Sports Medicine, Med 2011;45:2. http://dx.doi.org/10.1136/bjsm.2009.058594
Carl Heneghan: "Forty years of sports performance research and little insight gained", BMJ 2012; 345 doi: https://doi.org/10.1136/bmj.e4797
Cite this as: BMJ 2012;345:e4797