Exercise-Associated Hyponatremia during the Olympus Marathon Ultra-Endurance Trail Run

Research on hyponatremia during mountain marathons is scarce. The present study aimed to investigate the prevalence of exercise-associated hyponatremia during a 44-km trail running race that reached an altitude of 2780 m (Olympus Marathon). Sixty-two runners ( ve women) who completed the race participated in the study (age: 34.4 8.6 years; height: 1.77 0.06 m; and weight: 75.3 10.0 kg). Anthropometric characteristics, blood, and urine samples were collected pre- and post-race. Food and uid intake were recorded at each checkpoint. Due to race regulations, the runners could not carry any additional food and uids besides the ones provided at speci c checkpoints. Five runners (8%) exhibited asymptomatic hyponatremia (serum sodium<135 mmol L 1 ). Serum sodium in the hyponatremic runners decreased from 138.4 0.9 (pre) to 131.4 5.0 mmol L 1 (post),p<0.05. Plasma osmolality increased only in the eunatremic runners (pre: 290 3; post: 295 6 mmol kg 1 ;p<0.05). Plasma volume decreased more in the hyponatremic compared to eunatremic runners ( 4.4 2.0 vs. 3.2 1.4%,p<0.05). Lastly, dietary sodium intake was lower in the hyponatremic runners compared to eunatremic (789 813 vs. 906 672 mg;p<0.05). The incidence of

L 1 (post),p<0.05. Plasma osmolality increased only in the eunatremic runners (pre: 290 3; post: 295 6 mmol kg 1 ;p<0.05). Plasma volume decreased more in the hyponatremic compared to eunatremic runners ( 4.4 2.0 vs. 3.2 1.4%,p<0.05). Lastly, dietary sodium intake was lower in the hyponatremic runners compared to eunatremic (789 813 vs. 906 672 mg;p<0.05). The incidence of hyponatremia among the athletes was relatively low, possibly due to race conditions. Keywords: uid balance; dehydration; underhydration; electrolyte disorders; water intake 1. Introduction Marathon running and ultra-endurance events have gained signi cant popularity during the last decades worldwide [1,2]. Exercise associated hyponatremia (EAH) is a potentially life-threatening condition that can happen in athletic endurance events lasting more than four hours. EAH is de ned as a serum sodium concentration of less than 135 mmol/L during or up to 24 h after prolonged physical activity [3,4] and is mainly caused by excessive sodium loss via sweating and/or excessive drinking of hypotonic uids [5]. A high incidence of EAH has been documented mainly in ultra-endurance sports events but also in sports of shorter duration such as marathon [6–10]. Exercise-associate hyponatremia Nutrients2020,12, 997; doi:10.3390 /nu12040997 /journal/nutrients

Nutrients2020,12, 997 2 of 9 has been observed among marathon runners, cyclists, triathlon athletes, and recreational runners, participating most commonly in endurance events [3,4]. Data from studies carried out at the London and Boston Marathons indicate that EAH occurs in 10–15% of sampled marathon nishers [6,8,11]. EAH is predominantly dilutional hyponatremia caused by an increase in total body water relative to the amount of total body exchangeable sodium [3,4,12]. If not promptly recognized and adequately treated, EAH can be fatal via cerebral and/or noncardiogenic pulmonary edema. However, exercise-associated hyponatremia is still underestimated and, therefore, remains a medically signi cant problem for marathon runners. Moreover, educational interventions towards appropriate uid intake along with information about EAH's etiology and symptoms seem essential to reduce the risk and eventually, the incidence of EAH. Thus, the purpose of the present study was to investigate the prevalence of exercise-associated hyponatremia during a 44-km ultra-marathon mountain trail running race and examine the role of dietary sodium intake. 2. Materials and Methods 2.1. Subjects Sixty-two ( ve women) runners that successfully completed the race participated in the study. The inclusion criteria of the current study were: (1) age over 18 years old; (2) absence of orthopedic/neuromuscular injuries; and (3) previous experience with trail running races. The anthropometrical characteristics of the runners are presented in Table. Table 1.Characteristics of the study participants. Characteristics n=62 Age (years) 34.4 8.6 Sex (men/women) 57 /5 Weight (kg) 75.3 10.0 Height (m) 1.77 0.06 BMI (kg/m 2 ) 24.2 1.6 Participants were informed about the nature and purpose of the study and gave written informed consent. All procedures were in accordance with the Declaration of Helsinki, and the protocol was approved by the institutional review board of Harokopio University. Anthropometric characteristics, blood, and urine samples were collected and evaluated pre- and immediately post-race. In addition, nutritional behavior— uid and nutrient consumption—was assessed throughout the race. 2.2. Race Description The study was conducted during the o cial Olympus Marathon race, which is the most prominent mountain race in Greece. Runners covered 44 km on Olympus Mountain, of which 38 km are on mountain

and urine samples were collected and evaluated pre- and immediately post-race. In addition, nutritional behavior— uid and nutrient consumption—was assessed throughout the race. 2.2. Race Description The study was conducted during the o cial Olympus Marathon race, which is the most prominent mountain race in Greece. Runners covered 44 km on Olympus Mountain, of which 38 km are on mountain trails and 6 km on paved roads. The race started at 3 m above sea-level, reached a maximum altitude of 2780 m and nished at 300 m above sea-level. The winner of the race usually completes the marathon in less than 4:20 h, with a 10 h nishing time limit. The organizing committee of the race is exclusively responsible for providing speci c foods and drinks for the athletes, supporting them in 11 intermediate checkpoint stations throughout the mountain, approximately every 3–5 km. Athletes are not allowed to carry any other supplemental foods. The race is designated as an environmentally friendly race since it takes place on the Olympus Mountain, which is one of the Greek National Parks, also listed as a “World Natural Heritage Monument” by UNESCO (United Nations Educational, Scienti c, and Cultural Organization). Dropping trash along the race is strictly prohibited and leads to disquali cation. Mean environmental temperature and relative humidity during the day of the event ranged 15–34 C and 50–70%, respectively.

Nutrients2020,12, 997 3 of 9 2.3. Dietary Intake Two to three members of the research team were assigned to each of the checkpoints to record dietary intake during the race. The data were collected by audio-recording with the members of the research team mentioning the precise amount and type of uids and foods that the runners consumed. One size of cups were used in all checkpoints, and food availability was identical in all stations and provided by the race organizers. Since athletes were not allowed to carry and consume any drink or food besides the speci c checkpoints, any food and uid consumed in the 11 checkpoints represented the total amount consumed in the whole race. 2.4. Anthropometric Characteristics The day before the race, height was measured using a stadiometer with an accuracy of 0.5 cm (SECA 220, Seca Corporation, Columbia, USA), and body weight was recorded to the closest 100 g (Seca, model: 7701321004, Vogel & Hamburg, Germany). Body mass index (BMI) was calculated as body weight in kilograms, divided by the square of height in meters (kg/m 2 ). 2.5. Blood and Urine Analysis Blood samples were collected from runners following 15 min seated rest and analyzed immediately in duplicate for hematocrit (microhematocrit method) and hemoglobin (cyanmethemoglobin method, Drabkin reagent; Sigma-Aldrich, St. Louis, MO, USA), and the Dill and Costill equation was used to calculate changes in plasma volume [13]. In the remaining blood, serum and plasma were separated from the blood cells by centrifugation. Aliquots of blood plasma were used fresh for the determination of plasma osmolality by freezing-point depression (3D3 Osmometer; Advanced Instruments Inc., Norwood, MA, USA). The remaining blood plasma and serum were stored frozen ( 80 C) for subsequent analysis of serum glucose and creatine kinase serum sodium and potassium. Glucose and creatine kinase were measured by enzymatic analysis in an automated biochemical analyzer (ACE; Schiapparelli Biosystems Inc., Fair eld, NJ, USA). Electrolytes concentration was measured by selective electrode conductivity in an automated analyzer (Ektachem DT60 II system; Eastman Kodak Co., Rochester, NY, USA). Urine osmolality was measured in duplicate by freezing point depression

creatine kinase serum sodium and potassium. Glucose and creatine kinase were measured by enzymatic analysis in an automated biochemical analyzer (ACE; Schiapparelli Biosystems Inc., Fair eld, NJ, USA). Electrolytes concentration was measured by selective electrode conductivity in an automated analyzer (Ektachem DT60 II system; Eastman Kodak Co., Rochester, NY, USA). Urine osmolality was measured in duplicate by freezing point depression (3D3 Advanced Osmometer, Advanced Instruments Inc., MA, USA) and speci c gravity (USG) with a handheld refractometer (ATAGO SUR-NE, Tokyo, Japan). 2.6. Statistical Analysis All data are presented as means one standard deviation. Student t-test was performed to compare di erences between groups and paired t-test for pre- to post-race di erences. E ect size was calculated via partial eta square. Statistical analyses were performed with JMP Pro 14 (SAS Institute Inc., NC, USA). Statistical signi cance was accepted atp 0.05 for all tests. 3. Results Of the 62 volunteer athletes who participated in the study, ve (8%) experienced exercise-associated hyponatremia (serum sodium concentration of<135 mmol L 1 ). Only one of those ve runners experienced severe hyponatremia (<130 mmol L 1 ) with sodium levels of 122 mmol L 1 . Mean body weight decreased in both eunatremic and hyponatremic group, but the di erence between the two groups was not statistically signi cant (p 0.05, Table). Hyponatremic runners experienced a greater percentage of body weight loss than the eunatremic ones (p<0.05, Table). However, there were no signi cant di erences in nishing time and total uid intake between both groups. Hypovolemia after the race, as indicated by lower plasma volume, was greater in the group with hyponatremia compared to the eunatremic one (p<0.05).

Nutrients2020,12, 997 4 of 9 Table 2. Body mass, blood, and urine indices of pre- and post-race in eunatremic and hyponatremic runners. Eunatremic (n=57) Hyponatremic (n=5) PRE POST PRE POST Body Mass, kg 75.2 9.1 73.0 9.1 81.9 10.5 80.1 11.6 Change Body Mass, % - 2.4 3.2 - 3.0 2.2 y Finishing Time, h - 8.7 1.6 - 9.3 0.5 Hematocrit, % 42.0 4.4 43.9 2.9 39.7 5.2 43.2 5.3 Plasma Volume Change, % - 3.2 1.4 - 4.4 2.0 y Serum K + , mmol L 1 5.1 0.7 4.7 0.5 * 5.5 1.2 5.2 0.4 Serum Glucose, mg dL 1 94.1 19.3 86.5 28.7 95.3 21.0 83.9 35.9 Creatine Kinase, U L 1 162 115 994 772 * 173 98 1,516 1.213 * ,y Urine Osmolality, mOsm kg 1 721 343 768 288 622 341 729 78 Urine Speci c Gravity 1.026 0.011 1.034 0.012 * 1.024 0.012 1.032 0.005 Urine Na + , mmol L 1 187 233 72 43 * 152 98 41 19 * Urine K + , mmol L 1 42 31 77 38 * 30 11 98 36 * Urine K + /Na + Ratio 0.36 0.22 1.38 0.88 * 0.25 0.21 3.02 2.93 * ,y * Denotes statistically signi cant di erence from baseline value.yDenotes statistically signi cant di erence between eunatremic and hyponatremic runners. Serum sodium decreased in the hyponatremia group (pre: 138.4 0.9; post: 131.4 5.0 mmol L 1 ; p<0.05), while it was maintained in the eunatremic group (pre: 138.7 1.9; post: 139.2 3.4 mmol L 1 ; p 0.05; Figure). Eunatremic runners had higher serum osmolality after the race (pre: 290 3; post: 295 6 mmol kg 1 ;p<0.05), while no di erences were observed in the hyponatremic runners (pre: 291 3; post: 291 4 mmol kg 1 ;p 0.05; Figure). On the contrary, serum potassium signi cantly decreased in the eunatremic group (p<0.05), while it was maintained in the hyponatremic group (p 0.05; Table). Serum creatine kinase activation was signi cantly increased post-race (p<0.05) for both groups with the hyponatremic athletes exhibiting higher values, while serum

hyponatremic runners (pre: 291 3; post: 291 4 mmol kg 1 ;p 0.05; Figure). On the contrary, serum potassium signi cantly decreased in the eunatremic group (p<0.05), while it was maintained in the hyponatremic group (p 0.05; Table). Serum creatine kinase activation was signi cantly increased post-race (p<0.05) for both groups with the hyponatremic athletes exhibiting higher values, while serum glucose remained una ected (p 0.05) in both eunatremic and hyponatremic group.

Nutrients2020,12, 997 5 of 9Nutrients 2019, 11, x FOR PEER REVIEW 5 of 10 (a) (b) Figure 1. Serum sodium (a) and serum osmolality (b) level (Pre vs. Post) in eunatremic vs. hyponatremic runners. * Denotes statistically significant difference from baseline value. There was no significant change in urine osmolality between pre- and post-race for both eunatremic and hyponatremic groups (p ≥ 0.05; Table 2). However, USG significantly increased after the race only in the eunatremic group (p < 0.05). A significant decrease was observed in urine sodium post-race (p < 0.05), while the increment was observed in both eunatremic and hyponatremic group for urine potassium (p < 0.05). However, no statistical difference was observed between the two groups for urine sodium and urine potassium (p ≥ 0.05). Potassium-to-sodium ratio in urine was * * Figure 1. Serum sodium (a) and serum osmolality (b) level (Pre vs. Post) in eunatremic vs. hyponatremic runners. * Denotes statistically signi cant di erence from baseline value. There was no signi cant change in urine osmolality between pre- and post-race for both eunatremic and hyponatremic groups (p 0.05; Table). However, USG signi cantly increased after the race only in the eunatremic group (p<0.05). A signi cant decrease was observed in urine sodium post-race (p<0.05), while the increment was observed in both eunatremic and hyponatremic group for urine potassium (p<0.05). However, no statistical di erence was observed between the two groups for urine sodium and urine potassium (p 0.05). Potassium-to-sodium ratio in urine was increased in both

Nutrients2020,12, 997 6 of 9 eunatremic and hyponatremic runners (p<0.05), and the increment was higher in the hyponatremic runners (p<0.05). The results from the dietary intake during exercise are presented in Table. Dietary sodium intake during the race was signi cantly lower in the hyponatremic versus the eunatremic runners (p<0.05), while there was no statistical di erence in other nutrient intake (p 0.05). There was no signi cant di erence in uid intake between two groups (p 0.05). Table 3. Participants' energy intake, nutritional evaluation of macro- and micronutrient components, and uids consumption during ultra-endurance race. Dietary Intake during Race Eunatremic Hyponatremic Energy intake (kcal) 1525 717 1383 699 Carbohydrates (g) 264 122 236 98 Proteins (g) 43.9 32.7 43.5 35.9 Fat (g) 30.9 25.0 27.1 21.5 Sodium (mg) 906 672 789 813 * Fluids (mL) 3004 1228 2698 812 * Denotes statistically signi cant di erence between eunatremic and hyponatremic runners. 4. Discussion In the present study, we examined the prevalence of exercise-associated hyponatremia in a sample of runners participating in the Olympus Marathon. The incidence of mild and moderate hyponatremia was 8%, close to that observed in the previous studies mentioned above. The decrease in serum sodium in the hyponatremic group did not lead to lower serum osmolality. Interestingly, the increase in serum osmolality after the race in the eunatremic runners was not linked to changes in serum sodium. Changes in serum sodium and osmolality are tightly regulated in the body in order to maintain body uid homeostasis, and multiple factors could contribute to these adjustments, especially during the race, such as nish time and uid intake. No signi cant di erence in serum sodium concentration was observed in the eunatremic runners, yet serum osmolality increased by 5 mmol kg 1 , possibly due to changes in concentration in other osmotically active substances that we did not measure. However, it is unclear what led to this response in the current study. Body uids need to be replenished to prevent athletes from excessive dehydration during exercise [12]. However, uid overload is a dangerous practice during prolonged exercise, and it

mmol kg 1 , possibly due to changes in concentration in other osmotically active substances that we did not measure. However, it is unclear what led to this response in the current study. Body uids need to be replenished to prevent athletes from excessive dehydration during exercise [12]. However, uid overload is a dangerous practice during prolonged exercise, and it should be avoided [14]. The amount of consumed uid can vary among individual runners to compensate body uid loss [15]. Excessive uid drinking has been reported to be one of the factors that could cause EAH [16]. In the present study, no statistical di erences were found in total uid intake between eunatremic and hyponatremic groups. Exercise duration can also be a contributing factor in the development of EAH [6]. However, in the current data, no signi cant di erence in nishing time was found between eunatremic and hyponatremic runners. Exercise induced dehydration often leads to hypovolemia as a response to the uid de cit and exercise itself [17]. In the present study, even though the percent of body mass loss was greater in the hyponatremic group, no di erence was observed in the degree of hypovolemia. Presumably, given the race duration, a reasonably large component of the body weight loss could be attributed to glycogen loss and its associated water decrement. It has also been suggested that a decrease in serum potassium is associated with rhabdomyolysis in ultra-endurance runners, but whether this is prominent in the people with EAH remains controversial [18]. Although the decrement of serum potassium was less in the group with hyponatremia in the current study, the increment of serum creatine kinase was rather higher in this group (above 1000 U L 1 ), indicating signi cant muscle damage. Moreover, the signi cant increase observed in urinary K + /Na + ratio, especially in the hyponatremic group,

Nutrients2020,12, 997 7 of 9 suggests a parallel increased aldosterone activity, possibly due to endocrine-induced renal water retention, in order to maintain blood ow during prolonged exercise. High carbohydrate consumption is prevalent in endurance events lasting more than one hour. Exogenous carbohydrate intake during the race could maintain a high carbohydrate oxidation rate, sustaining the runner's pace, and maintaining euglycemia [19,20]. The guidelines from the joint position stand about nutrition and athletic performance suggest that during, endurance events longer than 2.5–3 h, the consumption of carbohydrates should be up to 90 g/h mainly through the provision of multiple transportable carbohydrates in order to maximize oxidation rate [19]. However, the relevant consumption of the runners in the present study was 31 14 and 25 10 g/h for the eunatremic and hyponatremic group, respectively, far below the aforementioned suggestions. Even though competitive ultra-endurance athletes may be more aware of their dietary sodium intake to reduce the risk of EAH [21], sodium intake level in the Olympus Marathon runners was small given the duration of the event [19]. Interestingly, the amount of sodium consumed by the runners that developed hyponatremia was signi cantly lower than that consumed by the eunatremic runners. These ndings, in combination, are in accordance with those from other studies, which clearly indicate that athletes fail to meet the suggested dietary needs, reducing consequently their potential for optimal performance [22–24]. As mentioned above, the primary etiologic factor of EAH appears to be the overconsumption of water and/or other hypotonic uids in excess of total body uid losses. Under these circumstances, inappropriate vasopressin secretion can reduce renal water clearance resulting in uid overload and dilutional hyponatremia [3,25]. Due to the race regulations, however, the runners could not carry along any extra personal uids, something that limited uid availability. Thus, overconsumption of water or any other hypotonic uids was unlikely to be observed. Even though some scientists argue that “drinking to thirst” is a good way to prevent exercise-associated hyponatremia, the race regulations enforced a drinking pattern more like “prescribed drinking” than “drinking to thirst”. A strength of the present study derives

The study investigates exercise-associated hyponatremia prevalence in runners during the Olympus Marathon.