Is Sodium Supplementation Necessary to Avoid Dehydration During Prolonged Exercise in the Heat?

Abstract

The primary purpose of this work was to gain further insight into the need for sodium supplementation for maintenance of appropriate hydration during prolonged exercise under hot conditions. Participants of a 161-km ultramarathon (ambient temperature reaching 39° C) underwent body weight measurements immediately before, during, and after the race, and completed a postrace questionnaire about supplemental sodium intake and drinking strategies during 4 race segments. The postrace questionnaire was completed by 233 (78.7%) race finishers. Significant direct relationships were found for percentage weight change during the race with intake rate (r = 0.18, p = 0.0058) and total amount (r = 0.24, p = 0.0002) of sodium in supplements. Comparing those using no sodium supplements throughout the race (n = 15) with those using sodium supplements each race segment (n = 138), body weight change across the course showed significant group (p = 0.022), course location (p < 0.0001), and interaction (p = 0.0098) effects. Posttests revealed greater weight loss at 90 km (p = 0.016, -3.2 ± 1.6% vs. -2.2 ± 1.5%, mean ± SD) and the finish (p = 0.014, -3.2 ± 1.5% vs. -1.9 ± 1.9%) for those using no sodium supplements compared with those using sodium supplements each segment. Six runners who used no sodium supplements, drank to thirst, and only drank water or a mixture of mostly water with some electrolyte-containing drink finished with mean weight change of -3.4%. Although the use of supplemental sodium enhanced body weight maintenance, those not using sodium supplements maintained a more appropriate weight than those consistently using sodium supplements. Therefore, we conclude that the supplemental sodium is unnecessary to maintain appropriate hydration during prolonged exercise in the heat.

Nutritional implications for ultra-endurance walking and running events

“…In fact, this shift appears to be a primary result of fluid overload and is unrelated to sodium losses [109]. To prevent over or underhydration, current available research suggests that the most suitable strategy to maintain hydration is to ‘drink to thirst’ [15, 27, 104, 109–112]. …”

“…Published data has shown that as high as 90–96% of ultra-endurance runners use sodium supplements [27, 29, 104]. Although past recommendations suggest a sodium intake of 1.7–2.9 g/L of fluid consumed to allow for fluid retention, more recent data have shown no benefit to hydration [19, 27–29, 104, 115] or blood serum sodium levels [19, 28, 29, 115] by consuming supplemental sodium during these races. This is likely due to the adaptations that increase sodium bioavailability and prevent losses (e.g.…”

“…These findings are possible indicators that the difficulty which athletes experience in meeting standard recommendations could be attributed to various factors. Among these are lack of or poor nutrition education, norms of ultra-endurance sports, the development of physical symptoms including injury, gastrointestinal disturbances, suppression of appetite, logistic challenges with implications for both food preparation in terms of time and available resources/facilities to do so and, by extension, total food intake particularly in those periods of increased needs [15, 26, 27]. Additionally, dehydration and fluid overload [14, 26–29] appear to be areas with which have challenges.…”

VIEW: Is Drinking to Thirst Adequate to Appropriately Maintain Hydration Status During Prolonged Endurance Exercise? Yes

“…Older humans are also thought to have a lower thirst sensitivity to hypertonicity compared with younger individuals. 5,6,27 Even when athletes begin aerobic exercise hypohydrated, the drive to drink during exercise is substantially magnified to optimally regulate plasma volume and osmolality 28 and endurance performance. 26 Field studies have also shown that drinking to thirst, even during prolonged exercise up to 30 hours under hot ambient conditions, will allow maintenance of what we consider to be proper hydration when considering mass loss from stored fuel.…”

REBUTTAL from “Yes”

“…Perhaps most importantly among the exceptions is the situation where thirst is driven by excessive sodium intake during exercise. Sodium supplementation is a common practice among endurance athletes, 3,4 and there is suggestion that excessive sodium intake can drive thirst, resulting in overhydration and even dilutional EAH 5,6 or pulmonary edema. 7 It is commonly stated that the sensation of thirst is not recognized until some dehydration has already developed, as was argued by Armstrong and colleagues.…”