Why not Hydrate with Salt?

Why not salt?

We get it, we lose salt when we exercise - so it makes sense in theory, to have salt in a hydration drink – but, it’s not that simple when the USDA Guidelines state that 90% of Americans consume too much sodium, which leads to elevated blood pressure and cardiovascular diseases.

UCSF has summarized data that shows the average American intake of salt is 20 times as much as the body needs… So why would we include it in a hydration drink?

Almost 90% of Americans exceed the recommended amounts of sodium. Even with strict dietary habits, it is really hard to be that 1 in 10 American, who doesn’t take in too much salt. The reason for this is that food items that may be perceived as being “not too bad for you”, still have significant amounts of salt. 

As per the USDA:

 

Even if you perceive your diet to be healthy, the vast majority of consumers of hydration products are getting too much salt. So, why would we add salt to a hydration product when the evidence is clear about the downstream effects on cardiovascular health?

But if we don’t replace salt during exercise, how will that affect performance?

Prolonged high intensity exercise may require salt supplementation. When we say “prolonged high intensity"  we are referencing: Ironman participants, ultra-marathon runners, long-distance cyclists - athletes whose demands related to the activity will limit their access to food for a significant portion of the day.

We know that those long-distance athletes who are not eating for long periods of the day (due to training or competition), can have transiently low sodium levels if their rigorous activity and sweating is only replaced with water.

But for 95% of athletes, exercise involves 1-3-hour duration (i.e. sporting activity or workout), that is usually accompanied by a meal in the 3 hours that precede the exercise, or the 3 hours that follow.

 In this population, salt supplementation in a hydration drink is NOT necessary for 2 reasons:

1. As per the USDA data above, 90% of Americans take in too much salt, and the average American takes in 20x as much salt as the body needs. This has far reaching implications on Blood pressure and cardiovascular disease.

2. The body tightly regulates sodium to prevent fluctuations. See the excellent schematic of a kidney nephron below  – your kidney is made up of millions of these filtering units that work to regulate your sodium levels, in addition to other functions. Look at all the sodium channels (Na+ = sodium) within the nephron… You can supplement with salt for your workout class/run/hike/sports activity, etc… but it’s not necessary, because the kidney’s job is to maintain homeostasis, and can regulate your salt losses during activity.  

(See kidney Nephron Map below)

An Ironman competitor or Ultra-Marathon runner will require salt supplementation due to the prolonged duration of the activity with significant salt losses through sweat. But, for 95% of people using hydration drinks, salt supplementation is unnecessary and dangerous over the long-term.

Evidence to support that additional salt-intake through a hydration drink is unnecessary for 95% of athletes and consumers of hydration products

Turner MJ, Avolio AP. Does Replacing Sodium Excreted in Sweat Attenuate the Health Benefits of Physical Activity? Int J Sport Nutr Exerc Metab. 2016 Aug;26(4):377-89. doi: 10.1123/ijsnem.2015-0233. Epub 2016 Feb 3. PMID: 26841436.

https://pubmed.ncbi.nlm.nih.gov/26841436/

International guidelines suggest limiting sodium intake to 86–100 mmol/day, but average intake exceeds 150 mmol/day. Participants in physical activities are, however, are often told to increase sodium intake before, during and after exercise to ensure euhydration, replace sodium lost in sweat, speed rehydration and maintain performance.

But, not so fast…

“Homeostatic systems (i.e. kidney and other internal organs that work to regulate electrolytes) reduce sweat sodium as low as 3–10 mmol/L to prevent excessive sodium loss.”

When we look at the physiological data, individuals who supplement with sodium during exercise seem to perpetuate their “salty sweat” condition by continual replacement of sodium excreted in sweat. (I.e. taking more leads to greater excretion through sweating)

Studies of prolonged high intensity exercise in hot environments suggest that sodium supplementation is not necessary to prevent hyponatremia during exercise lasting up to 6 hr:

1) A randomized controlled trial of sodium supplementation in athletes in an Ironman triathlon (Hew-Butler et al., 2006) “indicates that sodium supplementation is not required during high intensity exercise of long duration in hot conditions.”

2) Similarly, two studies of participants in four-hour route marches carrying 25–26 kg packs in 29 °C  (Nolte et al., 2011) and 24.5 °C (Nolte et al., 2010), indicate that “sodium supplementation is not required during high intensity exercise of long duration in hot conditions.”

3) Noakes and colleagues conclude that “65 mmol/day sodium is sufficient for healthy people during athletic activity” (Hew-Butler et al., 2006).

4) “The risk of hyponatremia is low if exercise is <4–6 hr (Hew-Butler et al., 2008; Coyle, 2004), even if pure water is ingested” (Barr et al., 1991).

So, although it is fair to say that an Ironman competitor will likely  benefit from supplemental sodium over the duration of a 6+ hour event… the vast majority of athletes will not require supplemental sodium during exercise because: 1) they eat food and 2) have kidneys, whose job is to maintain normal intracellular salt levels during exercise

For the long-distance athletes described above, we would make an argument that it would be reasonable based on the evidence, to consider an ½ strength apple juice hydration drink since we have RCT data to show that it decreases the risk of dehydration and is comparable to Pedialyte from a hydration standpoint. That type of quality data from a non-industry funded study is extremely rare among similar products in this field.

Look at all of those sodium (Na) channels! The body is complex… and it has a system for dealing with sodium loss through sweat. Just because you are losing salt through sweat, doesn’t mean that your intracellular sodium levels are low. You get enough salt through your diet, skip the added/unnecessary salt in your hydration drink!