We don’t need to replace sodium during endurance efforts after all?

Is everything we know about hydration wrong? Two podcasts worth listening too. Synopsis below.

@Dr_Alex_Harrison interested to hear your thoughts.

Does replacing the sodium lost in sweat actually influence our thirst, our drinking and our hydration? If so, how much is enough? And do we need to measure our sweat sodium losses to give us the answers? In this episode Alan describes his recently published study where ultra-runners replaced 100% or 0% of their sodium losses during 5 hours of running in the heat, and what happened.

Published trial


I only half listened to the first podcast between work but I thought he was saying at a certain level of intensity requiring little rehydration sodium replacement isn’t needed but at a higher rate of intensity requiring more rehydration it was important still. Basically the more fluid you need to take the more important sodium replacement is. And there was a grey area between over and under hydration and its individualistic to make it more grey.

No that’s not what he’s saying. The gist is; assuming you’re not rehydrating at 100% or more of fluid loss (which is pretty damn hard) then adding sodium would be of no benefit. He proves it in runs up to five hours in duration in the second one.

There is a tipping point. And he explains it well. But it’s for ultra endurance events.

It’s super interesting and well worth listening too. He goes into the percentage of fluid loss over the course of a session in detail and how that impacts whether sodium. Is required.


I haven’t listened. However, my queston is: is it “you don’t have to” or “you shouldn’t”?

Yes if you are not rehydrating 100% but if you are rehydrating at 100 % you do need it, that tipping point, the area in between seems unclear and rider dependent, he does seem to explain it well. For me I would think its not needed (I would agree with him) as I don’t hydrate enough but for other people it probably is (I’d also agree with him there)

@HLaB I didn’t listen to the podcasts (yet) but I’m able to confirm that different intensities result in different fluid AND ELECTROLYTE loss. Baker did some work on this and you can learn a lot about hydration/electrolyte needs by reviewing Baker and similar literature on this topic.

“Exercise intensity effects on total sweat electrolyte losses and regional vs. whole-body sweat”

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Attempts to know the un-knowable.

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And does the research thing, “it needs further research” :joy:

Good question. I listened to them when they first came out a few months ago. From what I recall, if you’re not hydrating 100% and your adding sodium you’re effectively increasing the salt content in your system.

Results are in the second podcast. Summation is, he had a bunch of people running on a treadmill for five hours. No difference between those who added salt and those who didn’t.

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Will give this a listen but All I know is if I don’t replace some of the electrolytes during a long ride/run I get banging headaches later on in the evening.


Me too. And I add 1000mg an hour.

Is the point of ingesting sodium to ward off cramps, sustain intensity or something else? All I know is that fluid, carbs and salt seem to really work for me when I’m riding long and hard.

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I learned over many years of riding that if I don’t ingest a lot of sodium on really long rides (5+ hours) I have horrible cramping issues. Very repeatable. I also look like I’ve been rolled in pretzel salt after hard rides. I’m a very profuse and salty sweater.


If I dont add salt I feel like I just have to pee every 30 minutes.

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I’ve only briefly read the study, not listened to the podcast. But initial comments would be:

  1. Be careful with terminology. Casual usage of the word “dehydration” is different than the medical usage. Dehydration in the medical sense is water deficiency and is frankly very uncommon. It manifests as an elevated serum sodium. Hypovolemia is loss of circulating blood volume and can be due to water deficiency, sodium deficiency, bleeding to death, etc. When lay-people are talking about “dehydration,” they are usually talking about hypovolemia. The symptoms people typically associate with “dehydration” are mostly those of hypovolemia.

(EAH is a different beast than dehydration/hypovolemia. Its causes are different in different people. Many people with EAH have SIADH as the cause for example).

  1. The main thing sodium supplementation during exercise does is prevent hypovolemia (ie prevent a loss in blood volume) when your other physiological mechanisms to prevent this have failed.

  2. This study took athletes whose sodium losses during exercise were known, and compared what happened when running 5h in 30C heat with sodium replacement or not. They were allowed to drink as much water as they wanted. They found really no difference in anything with sodium supplementation or not.

  3. The fact that these athletes were losing lots of sodium in their sweat, but did not become hypovolemic without sodium supplementation tells you that their bodies are really good at conserving sodium. They were able to adequately mobilize sodium stores from their bones to replace what they lost, and their kidneys prevented excessive sodium loss in their urine…. Successfully enough that this mobilized sodium plus the water they drank allowed them to avoid hypovolemia.

  4. What’s the take away point? In experienced and well-trained athletes, 5 hours of exercise in warm weather is inadequate to overwhelm their body’s sodium homeostasis. They can go eat a bunch of salt for dinner the next few days and make up their mild total body sodium deficit from the stores they dipped into (ex: bone).

Would 5 hours of biking in the heat overwhelm your body’s ability to maintain euvolemia/homeostasis with only water consumption? Who knows. It depends on how adapted you are to those conditions. If you do it and you start to develop symptoms of hypovolemia, then the answer is yes, so eat some salt now. If you feel fine, then great, go eat some salt slowly over the next few days to make up what you lost. Do you want to not have to worry about this in the middle of a ride? Great, add sodium to your water from the get go, because it’s certainly not going to hurt you.


I don’t have access to the full article. Would love to read it and give you my take on it if someone would like to share a copy. alex at saturdaymorning dot fit

Reading between the lines, the abstract seems to indicate lack of statistical power (low subject number, wide inter-individual variability) is the reason certain results did not reach statistical significance.

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Maybe this one, I didn’t listen to the podcasts

I listened to both of the the podcasts. I don’t necessary agree and there are many caveats, but the podcasts can be summed up with the following. Their takeaway is if you are doing moderate exercise (z2) for less than 4 hours and temperature is moderate, one must not be concerned with replacing sodium 1 for 1. You could probably just salt to taste. Replacing sodium appears to not affect performance or immediate recovery. Furthermore, one has more too risk (upset stomach/diarrhea) overdoing sodium than underdoing sodium.

So I guess don’t over salt your endurance rides.


Haven’t listened. Just in case someone doesn’t take in the nuances of the conversation, I would like to point out that at the end of a hot marathon, there are often several unconscious patients admitted to the ITU with severe hyponatremia brought on by taking in too much water and too little salt. It seems to be the fit club runner who achieves this, rather than the elite or jogger. They get better, but it isn’t an experience to recommend.

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Is there an optimal part of my body I should be tasting?