This article focuses on studies and resources related to hyponatremia, specifically exercise associated hyponatremia (EAH) for marathon and ultra-marathon runners. For general information on hyponatremia, please see the following article Singapore Hyponatremia Guidelines, Sports Safety in Singapore. We also have a more complete collection of studies on EAH to be found here.
Please note, these resources are shared for information purposes only. Always read the study itself (especially the Discussion section), do not rely on the Conclusion in isolation. Click on the links in the studies below to be taken to the relevant papers. If you have other studies to share, let us have them in the Comments at bottom of page. Include the citation and/or PMID if possible.
Always seek appropriate assistance for heat and hydration related medical situations; they can be life threatening. If you are considering changing your diet, exercise or lifestyle practices, please discuss plans with your primary medical practitioner before making any changes; especially if you are under treatment.
Stay Healthy,
Alastair
If you exercise in the heat, you might find these articles useful...
Studies on Hyponatremia
2023
Johnson KB, Connolly CP, Cho SP, Miller TK, Sallis RE, Hiller WDB. Clinical presentation of exercise-associated hyponatremia in male and female IRONMAN® triathletes over three decades. Scand J Med Sci Sports. 2023 Sep;33(9):1841-1849. doi: 10.1111/sms.14401. Epub 2023 May 19. PMID: 37204065.
"Conclusions: Altered mental status, vomiting, abdominal pain, muscle cramps, hypotension, tachycardia, and hyperkalemia appear to present differently between sexes when comparing hyponatremic to eunatremic athletes. Although overhydration is the most common etiology of hypervolemic hyponatremia, hypovolemic hyponatremia comprises a significant amount of hyponatremic triathletes. Further understanding of how EAH presents helps athletes and medical professionals identify it early and prevent life-threatening complications."
2022
López de Lara D, Ruiz-Sánchez JG, Cuesta M, Seara G, Calle-Pascual AL, Rubio Herrera MÁ, Runkle I, Verbalis JG. Exercise-Induced Hyponatremia: An Assessment of the International Hydration Recommendations Followed During the Gran Trail De Peñalara and Vitoria-Gasteiz Ironman Competitions. Front Nutr. 2022 Feb 21;8:781229. doi: 10.3389/fnut.2021.781229. PMID: 35265650; PMCID: PMC8898836.
"Conclusions: Recommending that athletes' fluid intake in endurance events be a function of their thirst almost entirely prevented development of hyponatremia, without induction of clinically significant hypernatremia, or a negative repercussion on race completion times."
Klingert M, Nikolaidis PT, Weiss K, Thuany M, Chlíbková D, Knechtle B. Exercise-Associated Hyponatremia in Marathon Runners. J Clin Med. 2022 Nov 16;11(22):6775. doi: 10.3390/jcm11226775. PMID: 36431252; PMCID: PMC9699060.
"Coaches need to educate their athletes about the early symptoms of EAH to intervene at the earliest possible stage. In addition, individual hydration strategies need to be developed for the daily training routine, ideally in regard to sweat rate and salt losses via sweat."
Lecina M, Castellar-Otín C, López-Laval I, Carrasco Páez L, Pradas F. Acute Kidney Injury and Hyponatremia in Ultra-Trail Racing: A Systematic Review. Medicina (Kaunas). 2022 Apr 21;58(5):569. doi: 10.3390/medicina58050569. PMID: 35629986; PMCID: PMC9146822.
"Conclusions: According to these results, extra and medium races showed a similar incidence of acute kidney injury (AKI) +EAH. These findings underline the importance of the duration and intensity of the race and may make them responsible for the etiology of these medical conditions. Due to their variable incidence, EAH and AKI are often underdiagnosed, leading to poorer prognosis, increased condition seriousness and hindered treatment. The results of this review urge participants, coaches and race organizers to take measures to improve the early diagnosis and urgent treatment of possible EAH and AKI cases."
Klingert M, Nikolaidis PT, Weiss K, Thuany M, Chlíbková D, Knechtle B. Exercise-Associated Hyponatremia in Marathon Runners. J Clin Med. 2022 Nov 16;11(22):6775. doi: 10.3390/jcm11226775. PMID: 36431252; PMCID: PMC9699060.
"There is variation in the reported prevalence of EAH, and two major studies indicated an incidence ranging from 7 to 15% for symptomatic and asymptomatic EAH. Athletes and coaches must be aware of EAH and its related problems and take appropriate measures for both training and competition. Coaches need to educate their athletes about the early symptoms of EAH to intervene at the earliest possible stage. In addition, individual hydration strategies need to be developed for the daily training routine, ideally in regard to sweat rate and salt losses via sweat."
2021
Khodaee M, Saeedi A, Harris-Spinks C, Hew-Butler T. Incidence of exercise-associated hyponatremia during a high-altitude 161-km ultramarathon. Phys Act Nutr. 2021 Sep;25(3):16-22. doi: 10.20463/pan.2021.0016. Epub 2021 Sep 30. PMID: 34727684; PMCID: PMC8580585.
"Conclusion: High altitude (3,840 m peak) does not appear to enhance the incidence of EAH after an ultramarathon footrace. This suggests that ambient temperature (low temperatures reduce risk), sex (female predilection), endurance running, and overhydration are more prominent risk factors for EAH than high altitude."
2020
Arnaoutis G, Anastasiou CA, Suh H, Maraki M, Tsekouras Y, Dimitroulis E, Echegaray M, Papamichalopoulou D, Methenitis S, Sidossis LS, Kavouras SA. Exercise-Associated Hyponatremia during the Olympus Marathon Ultra-Endurance Trail Run. Nutrients. 2020 Apr 3;12(4):997. doi: 10.3390/nu12040997. PMID: 32260197; PMCID: PMC7230381.
See study.
2019
Nolte HW, Nolte K, Hew-Butler T. Ad libitum water consumption prevents exercise-associated hyponatremia and protects against dehydration in soldiers performing a 40-km route-march. Mil Med Res. 2019 Jan 25;6(1):1. doi: 10.1186/s40779-019-0192-y. PMID: 30678725; PMCID: PMC6346586.
"Conclusions: Ad libitum drinking resulted in 4% body mass loss with a 2 mmol/L serum [Na+] reduction in conjunction with high urine osmolality (> 1000 mOsmol/kg H2O) and plasma AVP. No single hydration strategy likely prevents EAH, but hypernatremia (cellular dehydration) was not seen despite > 2% body mass losses and high urine osmolality."
Hoffman MD. Predicted Risk for Exacerbation of Exercise-Associated Hyponatremia from Indiscriminate Postrace Intravenous Hydration of Ultramarathon Runners. J Emerg Med. 2019 Feb;56(2):177-184. doi: 10.1016/j.jemermed.2018.10.026. Epub 2018 Dec 10. PMID: 30545731.
"Conclusions: Whether in the field or hospital setting, I.V. hydration of an athlete after an ultramarathon carries a notable risk for exacerbating EAH, so clinicians should use caution when hydrating athletes after endurance events."
Knechtle B, Chlíbková D, Papadopoulou S, Mantzorou M, Rosemann T, Nikolaidis PT. Exercise-Associated Hyponatremia in Endurance and Ultra-Endurance Performance-Aspects of Sex, Race Location, Ambient Temperature, Sports Discipline, and Length of Performance: A Narrative Review. Medicina (Kaunas). 2019 Aug 26;55(9):537. doi: 10.3390/medicina55090537. PMID: 31455034; PMCID: PMC6780610.
See study
2017 and Before
Tan DW, Yap SH, Wang M, Fan PW, Teo YS, Krishnasamy P, Krishna L, Hew-Butler T, Lee JK. Body Mass Changes Across a Variety of Running Race Distances in the Tropics. Sports Med Open. 2016 Jul 19;2(1):26. doi: 10.1186/s40798-016-0050-3. PMID: 27478761; PMCID: PMC4951505.
"Conclusions: Approximately 3-8 % runners had increased post-race body mass (BM), suggesting overhydration regardless of race distance. Symptomatic EAH was seen at race distances at or above 42 km, where BM changes demonstrated the widest range of values."
Lee JK, Nio AQ, Ang WH, Johnson C, Aziz AR, Lim CL, Hew-Butler T. First reported cases of exercise-associated hyponatremia in Asia. Int J Sports Med. 2011 Apr;32(4):297-302. doi: 10.1055/s-0030-1269929. Epub 2011 Jan 26. PMID: 21271498.
"In addition to the 3 cases of symptomatic hyponatremia observed, 8% of the 84-km runners and 7% of the 42-km runners gained weight during the race. This indicates the need to disseminate advice for the prevention and treatment of EAH for races held in the tropics."
Mohseni M, Silvers S, McNeil R, Diehl N, Vadeboncoeur T, Taylor W, Shapiro S, Roth J, Mahoney S. Prevalence of hyponatremia, renal dysfunction, and other electrolyte abnormalities among runners before and after completing a marathon or half marathon. Sports Health. 2011 Mar;3(2):145-51. doi: 10.1177/1941738111400561. PMID: 23016001; PMCID: PMC3445140.
"Conclusions: Metabolic abnormalities are common among endurance racers, and they may be present prerace, including hyponatremia. The clinical significance of these findings is unknown.
Clinical relevance: It is unclear which runners are at risk for developing clinically important metabolic derangements. Participating in prolonged endurance exercise appears to be safe in the majority of racers."
Related Studies
Pałka, T.; Rydzik, Ł.; Koteja, P.M.; Piotrowska, A.; Bagińska, M.; Ambroży, T.; Angelova-Igova, B.; Javdaneh, N.; Wiecha, S.; Filip-Stachnik, A.; et al. Effect of Various Hydration Strategies on Work Intensity and Selected Physiological Indices in Young Male Athletes during Prolonged Physical Exercise at High Ambient Temperatures. J. Clin. Med. 2024, 13, 982. https://doi.org/10.3390/jcm13040982
"Conclusions: All hydration strategies contribute to thermoregulatory processes and mitigate the rise in internal body temperature during sustained physical exercise in elevated ambient temperatures."
Veniamakis E, Kaplanis G, Voulgaris P, Nikolaidis PT. Effects of Sodium Intake on Health and Performance in Endurance and Ultra-Endurance Sports. Int J Environ Res Public Health. 2022 Mar 19;19(6):3651. doi: 10.3390/ijerph19063651. PMID: 35329337; PMCID: PMC8955583.
See Abstract.
Surapongchai J, Saengsirisuwan V, Rollo I, Randell RK, Nithitsuttibuta K, Sainiyom P, Leow CHW, Lee JKW. Hydration Status, Fluid Intake, Sweat Rate, and Sweat Sodium Concentration in Recreational Tropical Native Runners. Nutrients. 2021 Apr 20;13(4):1374. doi: 10.3390/nu13041374. PMID: 33923890; PMCID: PMC8072971.
"Conclusions: The sweat profile and composition in tropical native runners are similar to reported values in the literature. The current fluid replacement guidelines pertaining to volume and electrolyte replacement are applicable to tropical native runners."
Bouscaren N, Faricier R, Millet GY, Racinais S. Heat Acclimatization, Cooling Strategies, and Hydration during an Ultra-Trail in Warm and Humid Conditions. Nutrients. 2021 Mar 26;13(4):1085. doi: 10.3390/nu13041085. PMID: 33810371; PMCID: PMC8065615.
"Only 24.3% of study participants living in temperate climates declared having trained in the heat before the races, and 45.1% of all respondents reported a cooling strategy during the races. Three quarter of all participants declared a hydration strategy. The planned hydration volume was 663 ± 240 mL/h. Fifty-nine percent of the runners had enriched their food or drink with sodium during the race. The present study shows that ultra-endurance runners have a wide variability of hydration and heat preparation"
Nolte HW, Nolte K, Hew-Butler T. Ad libitum water consumption prevents exercise-associated hyponatremia and protects against dehydration in soldiers performing a 40-km route-march. Mil Med Res. 2019 Jan 25;6(1):1. doi: 10.1186/s40779-019-0192-y. PMID: 30678725; PMCID: PMC6346586.
See Abstract
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