title: 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.
authors.affiliation: 1Department of Physical Medicine & Rehabilitation, Department of Veterans Affairs, Northern California Health Care System, and University of California Davis Medical Center, Sacramento, California; and2Health Sciences Department, Gettysburg College, Gettysburg, Pennsylvania.
authors.forename: Martin D
authors.initials: MD
authors.lastname: Hoffman
authors.forename: Kristin J
authors.initials: KJ
authors.lastname: Stuempfle
mesh_terms: D000328:Adult; D003681:Dehydration / Q000517:prevention & control*; D004326:Drinking; D004573:Electrolytes / Q000008:administration & dosage; D005260:Female; D006358:Hot Temperature; D006801:Humans; D008297:Male; D008875:Middle Aged; D012420:Running / Q000502:physiology*; D012964:Sodium / Q000008:administration & dosage*; D011795:Surveys and Questionnaires; D013894:Thirst; D014882:Water-Electrolyte Balance; D015431:Weight Loss
chemical_list: D004573:Electrolytes; D012964:Sodium