Hi Reader,

We can't scroll through social media nowadays without being told we need to take electrolytes, that prevent several ailments (predominantly cramping) and improve our training. But, how much of it is BS marketing pushing a product that only gives you expensive urine vs. good science? Let's take a deeper look!

Do you need to be taking all those electrolytes?

We use and lose, three key things when we exercise that we replace, carbohydrate (muscle glycogen), water, and sodium (electrolyte). We have a good idea of the carbs and water (drink to thirst) and what the general guidelines are. Yet ask people about sodium and electrolytes, we all know it is important, just not why and how much we need to take as part of training.

We lose various electrolytes when we sweat, with sodium being the most significant. Potassium, calcium, and magnesium are lost in much smaller amounts, and their replacement isn't typically necessary. However, sodium (and chloride) losses can be substantial, especially for athletes with high sweat rates, potentially leading to significant depletion. Replacing sodium might seem straightforward, but the amount needed depends on understanding the purpose of the replacement. Determining how much sodium is required hinges on the underlying reason for taking it during a race, if at all it is required. Yep, you really may not need all those electrolytes, we are being pushed to take.

Why do we take sodium?

There are a number of assumptions on why we think we need to take sodium:

• Improve the absorption of carbs and fluid from the gut

Sports drink companies often claim that their unique formulations maximise fluid absorption for the fastest and most complete hydration. While this seems logical, the science doesn't fully support it. Rigorous studies, including those using invasive feeding tubes in the intestinal tract, indicate that sodium plays only a small role in fluid uptake in certain areas of the gastrointestinal tract, with no effect in others. Overall, the carbohydrate content of the drink or other foods consumed has a much greater influence on fluid absorption than sodium.

• Make us drink more (think thirst after a salty meal)

When we consume salty food, the salt concentration in the blood increases, raising blood osmolality, which signals the brain to trigger thirst. There's also some speculation that increased osmolality may be detected in the gut, stimulating thirst even sooner, though this hasn't been proven in humans. During exercise, increasing sodium intake has been shown to slightly increase the desire to drink, by about 100-200 mL per hour.

• Retain fluid in the body or blood

Evidence suggests that sodium replacement during exercise signals the kidneys to conserve water, reducing urine output and helping retain more fluid in the blood and around cells. This effect is due to sodium's impact on blood osmolality. While this might theoretically help maintain blood volume, reducing heart rate and body temperature, research shows that sodium's direct effect on these factors is minimal, unless it leads to significantly increased fluid intake and retention. Essentially, the benefits come from improved hydration, with sodium playing only a minor role in this process.

• For Performance

There are surprisingly few studies on sodium replacement and endurance performance, only five studies!! Four showed no effect of sodium on performance. The fifth, conducted during an Ironman 70.3 triathlon, found that athletes given sodium capsules performed 8% better than those on placebos, though this significant improvement raises scepticism about sodium being the sole cause, especially since strategies like carbo-loading or caffeine only improve performance by 1-4%. These studies also had various limitations, such as not being conducted in hot weather or personalising sodium replacement. More research is needed, but any performance benefit likely comes from improved hydration due to increased fluid intake, rather than sodium directly enhancing performance.

• Prevent muscle cramping (the one we all think)

Spoiler alert: Sodium plays only a minor role in cramping. Since cramping is influenced by diverse and individual factors, it’s unwise to attribute it solely to sodium, hydration, or any single cause. Cramping is multifactorial, and research shows that sodium is not a magic solution. While we've explored several reasons for replacing sodium during exercise, it’s clear that the process isn’t as simple as just replenishing what’s lost to avoid negative effects and cramps.

• To replace and stabilise blood sodium concentration

OK, this might help a bit with this one. Thirst, fluid retention by the kidneys, and water movement between cells, all depend on blood osmolality, which is influenced by blood sodium concentration. These effects rely on maintaining or slightly raising blood sodium levels during exercise. When we sweat but don't consume anything, our total body sodium decreases, yet blood sodium concentration increases, because sweat glands reabsorb some sodium but not water. Blood sodium typically remains within a very tightly controlled value of 135-145 mmol per litre. Contrastingly we know hyponatraemia (low blood sodium) is caused by drinking too much water.

What does mean for me and my training and racing?

The only real reason we need and want to replace sodium during exercise is to prevent a fall in blood sodium (not cramping or performance!!!), and this only happens when you drink close to or in excess of your sweat losses!!

Remember no fluid replacement causes blood sodium to rise, and replacing =>100% fluid makes it drop in concentration. Where's the point we may need to take Sodium? To keep it simple some examples are below:

• Running less than 4 hours, not needed. Yep you have enough stores in the body for anything shorter
• Over 4 hours and if sweating more than 1.8l an hour. The amount to drink every hour to justify sodium replacement is over 1.3l an hour. This is not practical in most situations and your gut has limitations. Sweat less, you don't need it!
• If replacing over 70% of sweat losses, then there’s likely to be a justification for taking sodium, especially if you have a higher salt concentration in your sweat. Think of running a 100miler, as a heavy sweater, with high sodium sweat concentrations
• If not, then using salt for taste is enough (think chips!

As you can see, there are some limited very specific scenarios when you may need to take sodium. Sports drink and electrolyte companies, athletes, social media and uninformed coaches often emphasise the importance of sodium replacement during exercise, but many of these claims don't align with the scientific evidence. The common message of replacing sodium to prevent a whole-body deficit (and cramp) doesn't hold up.

Instead, the potential benefits of sodium replacement are tied to maintaining stable blood sodium levels, which depends not only on the saltiness of your sweat but also on how aggressively you replace fluid losses.

Don't give yourself expensive urine!