Abstract
BackgroundSodium supplements are ubiquitous in endurance running, but their impact on performance has been subjected to much debate. The objective of the study was to assess the effect of sodium supplementation as a weight-based predictor of race performance in ultramarathon runners.MethodsProspective observational study during an 80 km (50 mi) stage of a 6-stage 250 km (155 mi) ultramarathon in Chile, Patagonia, Namibia, and Mongolia. Finish line hydration status as measured by weight change, point-of-care serum sodium, and questionnaire provided sodium ingestion categories at 33rd percentile and 66th percentile both for weight-adjusted rate and total sodium consumption, then analyzed for significant relationships to race performance, dysnatremia, and hydration.ResultsTwo hundred sixty-six participants were enrolled, with 217 (82%) with complete sodium supplement rate data, 174 (80%) with finish line sodium, and 161 (74%) with both pre-race weights and total sodium ingestion allowing weight-based analysis. Sodium intake ranged from 131–533 mg/h/kg (2–7.2 gm), with no statistically significant impact on pace, race time, or quintile rank. These outcomes did not change when sodium intake was analyzed as a continuous variable or by sub-group analysis of the 109 (68%) normonatremic runners. When controlled for weight-adjusted sodium intake, performance was poorly correlated with hydration (r = − 0.152, 95% CI − 0.348–0.057). Dehydrated runners outperformed those overhydrated, with 11% of top 25th percentile finishers dehydrated (versus 2.8% overhydrated), with 3.6 min/km faster pace and time 4.6 h faster finishing time.ConclusionsNo association was found between sodium supplement intake and ultramarathon performance. Dehydrated runners were found to have the best performance. This reinforces the message to avoid overhydration.
Highlights
Sodium supplements are ubiquitous in endurance running, but their impact on performance has been subjected to much debate
There were no significant differences in demographic variables between the sodium ingestion groups other than the low sodium category, which had a larger body mass index and run fewer ultramarathons compared to the two other sodium groups (Table 1)
Sodium supplementation per weight-based intake rate did not have any statistically significant associations with hydration, dysnatremia, or race performance, among other variables (Table 2) This did not change with a non-weight-based analysis. [(mg/h), Supplementary Tables 1 and 2] When sodium intake rate was examined as a continuous variable, no significant associations were found with percentile rankings (Fig. 1)
Summary
Sodium supplements are ubiquitous in endurance running, but their impact on performance has been subjected to much debate. Most studies fail to demonstrate associations between sodium intake and muscle cramps [4], or that supplements are protective against hyponatremia [2, 3, 5,6,7]. During periods of heat stress, it has been suggested that sweat sodium output changes in response to dietary intake [3] and sodium palatability increases [15]. These physiological mechanisms guard sodium homeostasis, which question the presumptive necessity of sodium supplementation during endurance exercise
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