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    Topic review

    Exercise-Associated Hyponatremia and Dehydration

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    Submitted by: José Martínez Sanz

    Definition

    During the last few years, the numbers of competitors in endurance and ultra-endurance sports modalities have increased significantly. This type of competition is an extreme challenge for athletes. Therefore, they have an increased the risk of developing medical and nutritional problems like exercise-associated hyponatremia (EAH), dehydration (DH); the provision of misinformation to athletes about nutrient intake and hydration during competition was identified as the main cause. These problems can affect the performance and health status of the athlete during and post-competition. Several nutritional guidelines have been suggested that can prevent these adverse outcomes, and it is essential to individualize and adjust the nutritional intake and hydration status according to the characteristics of each competition.

    1. Introduction

    Exercise-Associated Hyponatremia (EAH) is a disorder of fluids and electrolytes that has been widely described in marathon runners[1] and competitors in other endurance and ultra-endurance events such as: cycling races of 24 h or ≥150 km[2][3][4], foot races of 24 h or ≥100 km[2][5], Ironman triathlons[6][1], or open-water swimming events[4] [43]. It seemed to be a rare problem when it was first described in the scientific literature in 1985[1]; however, the current increase in the incidence of EAH should create alarm among athletes, since it has been confirmed as the cause of at least fourteen deaths, which reaffirms the potential severity of this condition[7].

    Studies suggest that ultra-endurance athletes competing in events that exceed 24 h, such as Ultraman, Titan Desert, or Sables Marathon participants, are at a higher risk of developing EAH compared to participants in shorter endurance tests, as could be the case of the marathon[1]. This is confirmed by the results obtained in different investigations, in which incidence rates of 6–18% were reported for Ironman[1][6], 6–11.5% in mountain biking events[2][4], and 15–30% in ultra- endurance running races[8][9], so the duration of the competition is a risk factor for EAH development in endurance and ultra-endurance sport modalities.

    For the proper management of EAH in athletes, it is important to make an early diagnosis. However, the signs and symptoms of EAH are nonspecific and can be superimposed on or confused with those of other diseases such as EHS, GI symptoms, and hypoglycemia, which are also frequent in these types of event. Special attention should be paid to the intake of large volumes of fluid, nausea, transient confusion, or exhaustion, as they can alert us to the development of these problems[10][11].

    2. Risk Factor

    The risk factors that have been identified regarding the development of EAH include: female sex, alcohol consumption, excess of fluid replacement, weight gain during exercise, low body weight, slow running performance and inexperience in endurance events[10]. Another problem that is related to EAH is Dehydration (DH) in athletes—which is sometimes followed by EAH, due to excessive hypo-osmotic fluid replacement. According to the results considered in this review, EAH can be also related to the environmental conditions that occur at the time of the competition, since at high temperature or humidity a greater loss of sodium can occur, in sweat[5]. Thirst should provide adequate stimulus for preventing excess dehydration and contribute to reduce the risk of EAH[7]. The incidence of DH may also reflect limited opportunities for the ingestion of fluid during competition and/or a lack of knowledge regarding the nutritional requirements of and fluid consumption by athletes[12].

    Since the water needs of athletes tend to differ depending on the individual characteristics and the type or intensity of the exercise in which they participate, individualized fluid replacement strategies are necessary. The American College of Sports Medicine (ACSM) recommends that fluid intake during exercise should limit body weight loss to <2%[13]. This view has been criticized on numerous occasions, as it may be inappropriate for athletes who begin the competition in a severe state of DH[12]. Therefore, and in accordance with the results obtained, the nutritional advice given to endurance and ultra-endurance athletes must include, in addition to adequate personalized and contextualized nutritional information, appropriate advice on hydration that takes into account the requirements of both the individual and the competition. This should result in the prevention of adverse outcomes and an improved performance of the athletes[14].

    Both the participants and the organizers of the competitions should be in possession of sufficient information and resources to help reduce the incidence of EAH and DH, ensuring above all the health and safety of all those who are encouraged to participate in endurance and ultra-endurance events.

    This entry is adapted from 10.3390/ijerph17114082

    References

    1. Christoph Alexander Rüst; Beat Knechtle; Patrizia Knechtle; Thomas Rosemann; Higher Prevalence of Exercise-Associated Hyponatremia in Triple Iron Ultra-Triathletes Than Reported for Ironman Triathletes. Chinese Journal of Physiology 2012, 55, 147-155, 10.4077/cjp.2012.baa010.
    2. Daniela Chlíbková; Thomas Rosemann; Lenka Posch; Radek Matou□Ek; Beat Knechtle; Pre- and Post-Race Hydration Status in Hyponatremic and Non-Hyponatremic Ultra-Endurance Athletes. Chinese Journal of Physiology 2016, 59, 173-183, 10.4077/cjp.2016.bae391.
    3. Lawrence E. Armstrong; Elaine C. Lee; Uglas J. Casa; Evan C. Johnson; Matthew S. Ganio; Brendon P. McDermott; Jakob L. Vingren; Hyun M. Oh; Keith H. Williamson; Hymn M. Oh; et al. Exertional Hyponatremia and Serum Sodium Change During Ultraendurance Cycling. International Journal of Sport Nutrition and Exercise Metabolism 2017, 27, 139-147, 10.1123/ijsnem.2016-0135.
    4. Beat Knechtle; Markus Gnädinger; Patrizia Knechtle; Reinhard Imoberdorf; Götz Kohler; Peter Ballmer; Thomas Rosemann; Oliver Senn; Prevalence of Exercise-Associated Hyponatremia in Male Ultraendurance Athletes. Clinical Journal of Sport Medicine 2011, 21, 226-232, 10.1097/jsm.0b013e31820cb021.
    5. Martin D Hoffman; Tamara Hew-Butler; Kristin J. Stuempfle; Exercise-Associated Hyponatremia and Hydration Status in 161-km Ultramarathoners. Medicine & Science in Sports & Exercise 2013, 45, 784-791, 10.1249/mss.0b013e31827985a8.
    6. Matthias Danz; Philip M. Tönjes; Klaus Pöttgen; J. Hinkelbein; Stefan Braunecker; Hyponatremia among Triathletes in the Ironman European Championship. New England Journal of Medicine 2016, 374, 997-998, 10.1056/nejmc1510409.
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    8. Martin D Hoffman; Kristin J. Stuempfle; Ian R. Rogers; Louise B. Weschler; Tamara Hew-Butler; Hyponatremia in the 2009 161-km Western States Endurance Run. International Journal of Sports Physiology and Performance 2012, 7, 6-10, 10.1123/ijspp.7.1.6.
    9. Jessica Rose Bruso; Martin D. Hoffman; Ian R Rogers; Linda Lee; Gary Towle; Tamara Hew-Butler; Rhabdomyolysis and Hyponatremia: A Cluster of Five Cases at the 161-km 2009 Western States Endurance Run. Wilderness & Environmental Medicine 2010, 21, 303-308, 10.1016/j.wem.2010.06.012.
    10. Ross S. Cairns; Tamara Hew-Butler; Incidence of Exercise-Associated Hyponatremia and Its Association With Nonosmotic Stimuli of Arginine Vasopressin in the GNW100s Ultra-endurance Marathon. Clinical Journal of Sport Medicine 2015, 25, 347-354, 10.1097/jsm.0000000000000144.
    11. Thomas M. Myers; Martin D. Hoffman; Hiker Fatality From Severe Hyponatremia in Grand Canyon National Park. Wilderness & Environmental Medicine 2015, 26, 371-374, 10.1016/j.wem.2015.03.001.
    12. Pamela J. Magee; Alison M. Gallagher; Jacqueline M. McCormack; High Prevalence of Dehydration and Inadequate Nutritional Knowledge Among University and Club Level Athletes. International Journal of Sport Nutrition and Exercise Metabolism 2017, 27, 158-168, 10.1123/ijsnem.2016-0053.
    13. Victor A. Convertino; Lawrence E. Armstrong; Edward F. Coyle; Gary W. Mack; Michael N. Sawka; Leo C. Senay; W. Michael Sherman; Exercise and Fluid Replacement. Medicine & Science in Sports & Exercise 2007, 39, 377-390, 10.1249/mss.0b013e31802ca597.
    14. Domínguez, R.; Mata-Ordoñez, F.; Sánchez-Oliver, A.J. Nutrición Deportiva Aplicada: Guía para Optimizar el Rendimiento; ICB Editores: Málaga, España, 2017; ISBN 978-84-9021-488-6.
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