Only recently a hot discussion among scientists about how much water one should drink during a longdistance endurance race like for example a triathlon race, was published in the British Journal of SportsMedicine. Before the 1980ies athletes were advised to avoid drinking during exercise, leading to the development of hypernatremia and dehydration in some athletes.
Since that time, it generally has been advised that athletes consume as much fluid as possible during exercise, and rates of fluid intake during running races varied widely from 400 to 1500 ml/h or even more. In fact, most race organizers currently provide copious supplies of water and „sports beverages“ throughout the race course to fend off dehydration. Concomitant with these recommendations, the incidence of hyponatremia in athletes seems to be increasing.
Water Balance: complex intertwined regulatory feedback loops
All in all, we may conclude that keeping the body fluid in balance is not that simple as one may think. It is not only drinking enough and taking salt tablets. The studies on the issue of water and salt balance are not conclusive at all. I think, because here again, we are confronted with complex regulatory feedback loops including among others hormones from the pituitary gland, central nervous circuits, peripheral inactive sodium stores, extracellular and intracellular water as well as osmotic active ions as there are sodium and potassium as the most prominent ones. Moreover, your individual body condition makes a difference too. Athlete is not like athlete, only the fact that some of you take round about 9 hours for a IRONMAN triathlon race and others may need 13 to 15 hours makes a huge difference. And there are environmental variables, of course that count. What is good for you, may not be good for somebody else. Therefore, you have to make your own experiences, find your own suitable way to keep in balance. It can always be dangerous to follow a recipe unquestioned.
Below, I cite some lines from a review that may give you an idea about this controversial topic
Exercise-associated hyponatremia* has been described after sustained physical exertion during marathons, triathlons, and other endurance athletic events. As these events have become more popular, the incidence of serious hyponatremia has increased and associated fatalities have occurred. The pathogenesis of this condition remains incompletely understood but largely depends on excessive water intake. Furthermore, hormonal (especially abnormalities in arginine vasopressin secretion) and renal abnormalities in water handling that predispose individuals to the development of severe, life-threatening hyponatremia may be present.
Until recently, the incidence of hyponatremia during endurance exercise was unknown and thought to be relatively uncommon. However, recent studies have shown that endurance athletes not uncommonly develop hyponatremia at the end of the race, usually in the absence of clear central nervous system symptoms. For example, in the 2002 Boston Marathon, Almond et al. found that 13% of 488 runners studied had hyponatremia (defined as a serum sodium concentration of 135 mmol/L or less) and 0.6% had critical hyponatremia (serum sodium concentration of 120 mmol/L or less).
Speedy et al. investigated 330 athletes who finished an ultramarathon race. In this study, 58 (18%) were hyponatremic (defined as a serum sodium <135 mmol/L) and 11 had severe hyponatremia (serum sodium <130 mmol/L). Studies of other endurance events have reported the incidence of hyponatremia to be up to 29% (9,10,12,15–25). These incidence rates may be overestimations as a result of sampling biases. For example, in the 2002 Boston Marathon study, of 766 runners enrolled in the study, only 488 runners had serum sodium values assayed. Some of these runners did not finish the race, and others had time constraints that did not allow them to have blood samples obtained. As is discussed later, the majority of these athletes are asymptomatic or mildly symptomatic (nausea, lethargy). However, severe manifestations such as cerebral edema, noncardiogenic pulmonary edema, and death can occur.
There have been at least 8 reported deaths from exercise-associated hyponatremia (EAH). Many of these reports relate to a series of fatalities in the military between 1989 and 1996. During this period, military recruits were encouraged to ingest 1.8 L of fluid for every hour they were exposed to temperatures above 30°C (30). At least four other deaths have been attributed to EAH in the United States. It is interesting that two of these deaths occurred in doctors. The exact incidence of mortality related to EAH is not known but is likely to be low.
