Why Sodium Is Crucial For Runners & Precision Hydration's Solution

Written by Precision Hydration Founder Andy Blow and edited by Precision Hydration Sweat Expert Abby Coleman.


Sodium plays a key role in how your body functions as it helps maintain fluid balance and cognitive function, so it's important to replace the sodium you lose to some extent when your sweat losses really begin to mount up.


Why Sodium Is Important

The main electrolyte in this extracellular fluid is sodium and much of your body’s total sodium reserves are found here. This makes it rather ‘salty’ and the total volume of extracellular fluid in your body is directly related to the amount of sodium you have on board at a given time. So, more sodium equals more fluid; less sodium means less fluid.

As well as maintaining fluid balance, sodium plays an important role in the absorption of nutrients in the gut, maintaining cognitive function, nerve impulse transmission and in muscle contraction. Basically, it's pretty darn important.


Most of the sodium we consume is in the form of sodium chloride, or the common table salt found in food and drinks. We take salt for granted these days as we've developed ways to make it widely available. But in ancient times wars were fought over access to salt and wages were even paid in it. The word 'salary' actually derives from the fact that Roman soldiers were often paid in salt, which gives you a pretty big clue as to its importance to life! Because your body can’t produce or store it beyond a certain point, you need to consume sodium every day to keep your levels topped up.


Individual differences in sweat sodium losses

Sweating is the main way athletes lose sodium and fluids during exercise. That's basically why those of us who train regularly have different needs when it comes to replacing sodium than those who don’t.

Everyone loses a different amount of sodium in their sweat. At Precision Hydration, we see athletes who lose from as little as 200mg of sodium per litre of sweat to as much as 2,000mg/l. I personally lose ~1,100 mg/l whereas Founder Andy loses ~1,800 mg/l. He often suffered from hydration issues in hot climates as a result and it was his personal search for a solution that led him to founding the company.

Sweat rates also vary from person to person of course; and from situation to situation for any given person (from almost nothing in cooler conditions and at low intensities, to several litres per hour during intense exercise in the heat).

When you combine differences in sodium concentration with those in sweat rates, the potential variance in the total net sodium losses experienced from one athlete to another can be really significant, especially over an ultra-endurance event!


What happens when sodium losses mount up?

It's impossible to nail down the exact point at which sodium (and fluid) loss through sweating becomes a problem for an athlete. But, it's clear that when losses reach a certain point, the effects can be detrimental to your performance.

Your blood volume is gradually reduced as your sweat losses increase. That’s because sweat is drawn from your blood plasma. This increases the strain on your cardiovascular system, making it harder to pump blood to your skin to cool you down and to your working muscles.

Other issues such as a general feeling of fatigue and muscle cramps can also be experienced if losses are allowed to go uncorrected for long enough, or if significant imbalances between fluid and sodium are allowed to occur.

Up to a certain point, taking in plain water is enough to mitigate sweat losses. But, as those losses start to mount up, you need to replace sodium too in order to avoid your blood becoming diluted. This is a potentially disastrous condition called hyponatremia, which can certainly ruin your race and, tragically, has even been fatal on occasion.


How much sodium should you replace when sweating?

Because sweat/sodium losses are so individual, any generic guidelines on the replacement of sodium and fluid should always viewed with suspicion. Having said that, figuring out whether your net losses are likely to be low, moderate, or high can be a great starting point for homing in on the level of sodium and fluid replacement that'll work best for you in different circumstances.

The two main inputs that drive your personal net sodium losses are...

1. The total amount you sweat. This is a factor of your sweat rate and the number of hours you spend sweating during a given time frame.

2. Your sweat sodium concentration. i.e. how much salt you lose in your sweat.

Figuring out approximately what these are is a sensible place to start.

Calculating your sweat rate can be a bit awkward, but here's a guide to help you get you to a reasonable estimate of how much you're sweating per hour.

Your sweat sodium concentration is largely genetically determined and doesn’t vary much at all which means that, whilst you can only find it out by getting your sweat tested, you only really need to get tested once in most cases. We offer an at-rest, non-invasive sweat test at Sweat Test Centers around the world for anyone wanting to find out exactly how much they're losing.

We also offer a free online Sweat Test that'll help you get started with understanding your losses and refining your hydration plan through some good old fashioned trial and error in training.

If you have any hydration-related questions that haven’t been answered in this blog, feel free to reach out to the PH team on hello@precisionhydration.com.

Feel free to use the code TM-OVERTHEFELLS to get a 15% discount when trying out Precision Hydration for the first time!

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