Supplementation with 1800 mg sodium did not see a significant effect on sweat rate, cardiovascular drift, heat stress, skin temperature, rating of perceived exertion or time to exhaustion in the trained endurance athletes, according to the results published in the Journal of Sports Science and Medicine.
Either way the researchers urged caution for athletes using such products for this reason given the adverse effects of high sodium intakes for example hypertension and the fact that many individuals already consume high amounts of sodium through their diet.
The good, the bad and the sweaty
Sodium is the main electrolyte lost during heavy sweating and therefore athletes sometimes take sodium supplements to compensate for this loss.
However the scientists from Saint Louis University in the US said the impact of this increased sodium on thermoregulation was less clear, with past research suggesting it could hinder the body’s ability to regulate temperature by reducing how much sweat was produced.
In 2011 the European Food Safety Authority (EFSA) approved a health claim stating: “Sodium is needed for the functioning of muscles.”
However, the claim was later rejected by member states and the Commission due to concerns over what this would tell the general population about sodium intakes and health.
The European Specialist Sports Nutrition Alliance (ESSNA) has given this as an example of how special nutritional needs of sports people are not considered in EU food law.
They also looked at cardiovascular drift whereby heart rate increased during exercise without having increased exertion. This may be due to an increase in body temperature or loss of water through sweat, which meant the blood was more viscous and therefore the heart must work harder to transport the same amount of oxygen to the muscles.
Both these factors were said to impact performance – increased sweat improved performance and cardiovascular drift may hinder performance.
Results at the finish line
Based on previous findings, it was hypothesised that high-dose salt supplementation during two hours of endurance exercise would decrease sweat rate, increase heat stress, decrease the magnitude of cardiovascular drift, decrease perceived exertion and increase time to exhaustion.
However the results of their tests questioned both these positive and negative speculated effects of sodium.
In the study, 11 endurance athletes underwent two hours of endurance exercise at 60% heart rate reserve twice, once given sodium capsules and once a placebo, followed by a performance test.
In the sodium trial, one sodium capsule – containing 360 mg sodium and 540 mg chloride – was given immediately before starting the test and every 25 minutes thereafter (at minute 25, 50, 75 and 100). Participants received a total of 900 mg of sodium per hour.
Sweat rate was calculated from changes in body weight, accounting for fluid intake and urinary losses. Ratings of perceived exertion, heat stress, cardiovascular drift and skin temperature were also measured.
Dehydration occurred in both the sodium and placebo trials and no significant difference was seen for any of the other measures across the two trials.
Source: Journal of Sports Science and Medicine
Vol 14, Iss 1, pp. 172–178
“Effects of Oral Sodium Supplementation on Indices of Thermoregulation in Trained, Endurance Athletes”
Authors: E. Earhart, E. Weiss, R. Rahman and P. Kelly