Can sodium help performance?

In previous blogs we’ve discussed what sodium is and how it might be helpful during exercise. In this article, Dr Alan McCubbin will take a look at the scientific studies that have explored consuming sodium during exercise, and whether it improves performance.

A table with all performance studies showing that there is little evidence that sodium can improve performance

How many studies on sodium intake and performance are there?

As part of my PhD on sodium for endurance athletes, I conducted a systematic review, a comprehensive sweep of the academic literature to find any and all studies that have investigated sodium replacement during exercise and subsequent endurance performance. Whilst I was aware that not much had been done in this space, even I was surprised to find only five studies ever published on the topic.

What did they find?

Of these five studies, none of them were conducted in hot conditions (temperatures varied from 2.6-22.5°C). None of them personalized the athlete’s sodium replacement either, instead giving the same amount to each participant, usually estimated as the average expected loss. It is likely then that some participants received too little sodium to replace their losses, whilst others replaced more than what they lost during exercise. Whilst some studies allowed the participants to drink as much or as little fluid as they liked (replacing sodium did make them drink more in the studies that measured this), one study provided a prescribed amount that was so great that a significant proportion of the participants developed mild hyponatraemia by the end. This same study also had participants exercising outdoors on two separate days, with temperatures so different (as low as 2°C on one day and 20°C on the other) that performance was more likely to be influenced by the weather than the sodium.

Of all the studies (four outdoor, one in the lab), only one showed any benefit from sodium supplementation, and it involved 26 male competitors in an actual Ironman 70.3 triathlon taking salt or placebo capsules. However, other factors on the day like competitors and transitions may have influenced this result, and the reported benefit in the sodium supplemented group (26 minutes, or an 8% improvement) is well beyond what would be expected from any nutritional intervention, such as optimised hydration or carbohydrate intakes.

Of all the studies (four outdoor, one in the lab), only one showed any benefit from sodium supplementation and there are questions marks about the reliability of that study.