Are electrolytes important for athletes?

In this series of blog posts, we’ve discussed what is meant by the ‘electrolytes’, that are promoted in sports nutrition products. We’ve looked at how much you actually lose during exercise, and what role they play in athlete health and performance during exercise. So far we’ve seen that:

Electrolytes for athletes: is it all hype or is there some science too?

  • Electrolytes are minerals that dissolve in water into their individual, positively or negatively charged ions: Sodium: Na+ and Potassium: K+ Chloride: Cl- Magnesium: Mg2+ and Calcium: Ca2+ and many others

  • Sodium and chloride are the two electrolytes lost in large quantities through sweat, but these losses are also regulated in response to the balance of sodium consumed in the diet and recent sweat and urine losses.

  • Sodium added to drinks before exercise can improve the amount of that fluid retained, rather than lost through urination.

  • Sodium added to drinks during exercise improves their flavour and tends to encourage consumption, which can be useful in terms of preventing excessive fluid losses during exercise. The effect on fluid and carbohydrate absorption from the gut is likely minimal.

  • Sodium during exercise can also reduce the fall in blood osmolality and reduce (but not eliminate) the effect of aggressive fluid replacement on the risk of developing hyponatraemia. However, only when athletes exercise for more than 4 hours, and are likely to drink to replace >70% of their sweat losses does the process of sweat sodium testing and targeted replacement appear necessary. Even then, only those athletes with above average sodium concentrations in their sweat (>1g/L) are likely to need to specifically focus on sodium replacement during exercise.

  • Whilst there are only a few studies in this area, and many have specific methodological concerns, there is currently little evidence that replacing sodium during exercise will improve performance in the same way that adequate carbohydrate or fluid intake will. However, as per the point above, if aggressive fluid replacement is undertaken, then sodium replacement will be useful to balance that fluid intake and maintain a stable blood osmolality.

  • Other electrolyte losses in sweat are minimal and don’t appear to need specific replacement during exercise.

Only when athletes exercise for more than 4 hours, and are likely to drink to replace >70% of their sweat losses does the process of sweat sodium testing and targeted replacement appear necessary.

So are we replacing sodium losses, or balancing water turnover?

When we think about consuming carbohydrate or fluid during exercise, we’re either thinking about topping up a finite store of a fuel that is preferentially used to fuel the demand of working muscles (carbohydrate), or preventing the negative effects that an overall deficit has on health and performance (fluid). This is the same lens through which the majority of athletes and coaches tend to think about sodium – that when a certain amount of sodium is lost from the body without replacement, that something will go wrong physiologically that leads to either detrimental health or performance outcomes.

Interestingly, research over the last few decades suggests that humans do in fact have stores of sodium in