Prospective Observational Study of Weight-based Assessment of Sodium Supplements on Ultramarathon Performance (WASSUP)

Abstract

Background: Sodium 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.

Methods: Prospective 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.

Results: Two 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.

Conclusions: No 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.

Keywords: Dehydration; Electrolytes; Endurance; Exercise-associated hyponatremia; Overhydration; Performance; Running; Supplements; Ultramarathon.

Fig. 1

Weight-adjusted sodium intake versus performance from percentile based groupings. Sodium intake does not appear significantly correlated with rank-based performance. Extreme outliers in sodium consumption (four values > 10) were excluded to improve plot readability

Fig. 2

Pearson’s product moment-correlation coefficient and 95% confidence interval for pace and sodium intake rate controlled for similar paced runners using percentile based grouping.

Fig. 3

Similar paced runners correlated with pace versus sodium intake in hot versus cold climates. This plot demonstrates a lack of overwhelming evidence for correlation between sodium intake and performance at any performance level. Each race pace group corresponds to a sliding window of the 20 runners with the most similar overall race performance according to average pace. Pearson’s product moment correlation is used to assess linear relationship between pace and sodium intake. Each bar gives the correlation value and 95% confidence interval