Sodium – Do we need it?

You may have already seen this article on Mile27 from Andy DuBois, but he’s also very kindly allowed us to report here in Ultra168 too. I jokingly called this the ‘Great Big Salt Con’ when discussing this article with Andy a few weeks back, but he of course can offer up a far more eloquent dialogue that I. Thanks to Andy for allowing us to repost…

The ability to measure our sodium losses in sweat during exercise has led some to thinking that we need to replace at least some of what we lose in sweat to ensure our blood sodium levels don’t fall to levels that affect performance or health.

The thinking goes that somewhere between 230-1700mg of sodium can be lost per hour during exercise in hot conditions and we have a typical daily intake of 4g. As a consequence it can take only 2-3 hours before we deplete our sodium stores levels that affect performance. But measuring sweat sodium levels is only part of the picture – our body doesn’t particularly care what our sweat sodium concentration is (and in fact it reduces sweat sodium concentration as it acclimatises to exercising in the heat). What the body very tightly controls is our blood sodium levels and has several mechanisms to keep it within 135-145 mmol/litre range that is required for normal human function.

One thing to understand is that it’s not the actual amount of sodium in our body that is the critical factor, it’s the concentration of sodium in our blood. If there is less blood then we need less sodium to keep the concentration in normal range.

Deciding we need sodium supplementation based solely on what we sweat out is like basing fat consumption based purely on how much fat we burn during exercise or basing our hydration strategy purely on how much weight we lose or our carb intake on how much energy we burn when we run. What we burn or sweat out doesn’t matter – it’s what’s left in the body that we need to be concerned about. So when we look at fat burnt during exercise we know that we have ample supplies of fat so there is no need to take on additional fat, we know that our carb supplies will eventually run out so we need to take in additional carbs in a race but we know we don’t have to replace the whole amount we burn, we also know that the body can handle a certain level of dehydration with no adverse effects provided we drink to thirst. As far as sodium goes what we should be looking at is what happens to our blood sodium levels during exercise NOT how much sodium we lose in sweat.

Do we need to replace all of our sodium sweat losses, some of them or none of them?

How does exercise affect our blood sodium levels?

If we look at effect of endurance exercise on blood sodium levels we find something very interesting. Tim Noakes in his book Waterlogged has a table (pg 129-130) listing 30 studies over a 45 year period that measured blood sodium levels pre and post a number of different endurance events. In only one study were there any subjects that had a lower blood sodium level then when they started. In every other study EVERY participant had a higher plasma sodium level post race compared to pre-race.

Think about that for a second – over a period of 45 years researchers consistently found that post exercise blood sodium levels ROSE regardless of what they drank (in most of the studies the participants only drank water). The only logical conclusion to this is that blood sodium concentrations always rise during exercise.

How can blood sodium levels rise when we know we lose sodium in sweat and urine?

Remember it is the concentration of sodium in blood that is tightly regulated not the actual amount of sodium. So if sodium is lost and blood volume is reduced (through dehydration) in an equal amount then concentration stays the same. So as we sweat we lose both fluid and sodium but since our sweat is less concentrated than blood our blood sodium concentration increases.

What about salty sweaters – surely they need more sodium?

In fact, the opposite has been shown.

A study on Indian soldiers in 1960 (1) measured sodium loss in urine and sweat for soldiers exercising 2 hours a day in 35-degree heat. The soldiers were split into different groups, each group on a strictly controlled sodium diet. Researchers found the more sodium in their diet the more sodium in their sweat and urine.

Another study of U.S Soldiers in the desert by Adolph 1947 (2) found that those that ate a higher salt diet had more salt in their sweat and urine

How much sodium can we lose before we begin to suffer any effects?

In a study by Armstrong, Hubbard et al 1983 (3) subjects on a 4g a day sodium diet ( average Australian intake is around 6g per day) exercised for 30 minutes each hour for 8 hours per day in 41-degree heat. (Not a study many of you would be keen on signing up for that’s for sure!) After 17 days of the experiment there were no cases of heat exhaustion, heat cramps, heat stroke and blood sodium levels remained in the normal range for the duration. Consider the subjects lost 60 litres of sweat over the period and drank nothing but water. It seems obvious that we can survive a long time with very little sodium, well beyond the length of any endurance event. Even multi-day events don’t pose a problem since at the end of each day you consume a normal meal containing salt.

What about people who found that they can now complete races without cramping through the use of sodium supplementation?

Since we know that blood sodium levels aren’t low in crampers one possible explanation is that sodium triggers a reflex in the back of the throat which then triggers a neural reflex that relaxes the cramp. I’ve discussed this before here

So if you cramp often then first of all look at training and tapering and if you feel a cramp coming use a salty solution as a mouthwash – no need to ingest it.

Is there a danger of taking in too much sodium?

According to Dr Marty Hoffman ( Director of Research at the Western States Endurance Race) in the 2014 Practise Guidelines for Wilderness Emergency Care “Adverse effects associated with abnormal water retention from excessive sodium intake have been reported” and he has also shown data from the 2011 Western States Endurance Run where some runners finished the race hyper-hydrated (i.e. carrying more weight than when they started) and had sodium levels that were above the normal range. These runners consumed between 25 and 60 S! Caps each. Now that may seem like a lot by for 24-hour runners that’s only 1-2 per hour which is well within recommendations given by the manufacturers.

This conclusion by Earhart et all (4) sums it up

“High-dose sodium supplementation does not appear to impact thermoregulation, cardiovascular drift, or physical performance in trained, endurance athletes. However, in light of the possibility that high sodium intakes might have other adverse effects, such as hypertension, it is our recommendation that athletes interpret professional recommendations for sodium needs during exercise with caution.”

What about the arguments for sodium supplementation

Despite the above there are some people who still claim to have evidence to support sodium supplementation. But if low sodium levels are truly the cause of cramp or poor performance then we must see a correlation between low blood sodium levels and cramp or poor performance and that’s not the case at all in numerous studies. They all confirm there is no difference in incidences of cramp or a correlation to performance if you take sodium or not.

There are claims that people who cramp have higher sweat sodium losses which makes sense when you think about it. The more acclimatised you are the lower your sodium loss in sweat. If you take two people with the same fitness, but one is more acclimatised than the other then the more acclimatised athlete will be able to perform at a higher level of intensity in warmer conditions compared to the unacclimatised person. We all know what happens if you go out too hard in hot conditions – cramp. The central governor is telling the unacclimatised person that they are going out too hard and one way to slow them down is cramp, nothing to do with low sodium levels.

The pro salt side may tell you that there is a greater risk of hyponatremia when consuming water alone rather than a liquid containing sodium. Given that the sodium concentration we are able to digest is far lower than the concentration of sodium levels in the blood, whether you take water or a sports drink containing sodium you are still diluting your blood sodium levels. If you drink too much water it doesn’t matter if it contains electrolytes or not you’ll end up with hyponatremia.

If not consuming salt was a risk factor in hyponatremia then we would expect to see athletes that only drank water during endurance exercise in hot conditions to have a greater chance of dangerously low sodium levels. As we discussed earlier Noakes listed over 30 studies showing that blood sodium levels remained in normal ranges during endurance events when drinking only water .

The biggest risk factor for hyponatremia is a body weight gain during exercise which comes from drinking too much water. Whether that water contains sodium or not makes no difference. This was confirmed in study in 1991 by Barr et al that found that blood sodium levels dropped in subjects that drank 1.15 litres of water per hour by equal amounts whether they drank a saline solution or plain water. The volume consumed was calculated to be the volume needed to prevent any weight loss during exercise.

If you only take one point from this article let it be this one from the study by Barr:
In subjects that drank sufficient fluid to suffer no weight loss at all during exercise, blood sodium levels dropped whether they consumed plain water or sodium

Another excellent argument NOT to weigh yourself before and after exercise and use that as your basis for how much fluid you should consume during exercise. Drink to thirst and don’t bother taking sodium – it makes no difference.

So assuming you consume salt in your diet there is absolutely no need to take it during training or racing. If you often cramp then look at your training, tapering and pacing in races and take a small solution of pickle juice to hold the cramps at bay if they occur.


1. Malhoutra MS Salt and water requirement of acclimatised people working outdoors in severe heatInd J Med Res 1960

2. Adolph EF Urinary excretion of water and solutes. Physiology of man in the desert 1947

3. Armstrong LE Hubbard RW, Askew EW et al – Responses to moderate and low sodium diets during exercise-heat acclimation. Int J Sport Nut 1993

4. Elizabeth L. Earhart, Edward P. Weiss, Rabia Rahman, Patrick V. Kelly
Effects of Oral Sodium Supplementation on Indices of Thermoregulation in Trained, Endurance Athletes. J Sports Science Medicine (2015) 14,

5. Barr SI, Costill DL, Fink WJ, Fluid replacement effects of water, saline or no fluid. Med. Sci. Sports Exerc. 1991

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5 thoughts on “Sodium – Do we need it?

  1. Is it possible that sodium is pulled from muscle cells to keep the blood sodium level constant while running. If too much is pulled from working muscles, then those muscles cramp. By slowing down, the need for feeding sodium to the blood decreases and the cramp subsides, much as it would by adding sodium to the blood via ingestion.

    I always cramp during races between 3 and 4.5 hours into them if I do not start supplementing with salt from the start. I also naturally slow down after 5 hours also. I am 65 and have been running for 22 years. I have completed 139 26.2 mile marathons and another 136 longer races including 45 100-mile races out of 80 attempts.

    1. Thanks for your comments Allan – that is one theory that has been mentioned before – it is my understanding that Sodium ions are at a greater concentration outside the muscle cell than in. When the muscle cell is innervated then sodium rushes from the blood into the muscle cell creating an electrical potential which sets of the trigger of chemical events that causes muscular contraction . Then the sodium potassium pump operates to pump the sodium back out of the muscle cell restoring the cells resting potential .

      The theory of muscles topping up blood sodium levels would require blood cells to detect low blood sodium levels and have a store of sodium they can release but at rest muscles have more sodium outside than in so I dont think that theory stacks up .

      But I’ll admit my understanding of the chemical workings at that level certainly could be better , I’ll see if I can get an answer from someone with far greater understanding and get back to you

    2. Hi,
      This ‘con’ as U168 says, has been spoken about on forums etc, and prior to that since I started running (and studied Biochem at Uni) as far as I can remember, and that is a continuous 39yrs now of marathon running, and is something that I have followed and ‘studied’ for decades…….couple of specifics:
      1) This was summarised quite well by Ross Tucker of Sports Scientists (science of sport previously).

      2) No evidence to support Sodium(or Magnesium) loss with cramps and people who sniff a particular sodium product, or ingest a tablet and suddenly get relief do not understand that it is impossible for sodium to get to affected area that quick if it was the bad actor…and do not understand placebo, nor the fact that their stop to take the tablet and stretch is more of a relief than anything else.
      ps…I have a very low salt diet and have never ever cramped, so it is a personal muscle reaction to continuous and repetitive action, exacerbated by incorrect training and running form.

      3)Excessive sodium consumers simply strain their ADH system, blood pressure issues as it compensates with volume, and simply sweat more. You can just see the caked white faces and armpits of the people with high salt diets…nothing new here. an aside, when running in Cape Town’s ‘Cape Flats’ in 80’s, anecdotally you found that poorer guys from townships were very much caked with salt after races and I often spoke to them about their diets…it was a combination of education, and an imbalanced diet (they simply ate what was on the table right?).

      4) As indicated by Tucker’s summary and in article, you cannot replace the concentration in your sweat with electrolytes, nor should you even try to. The best liquids ‘on the run’ are isotonic.

      5) Hyponatraemia is caused by excessive drinking rather than lack of sodium. …which is why it is almost exclusively prevalent in long ultras where there is too much time for drinking and too slow a pace to match what is being consumed. Dehydration is almost impossible in these events, and in fact dehydration due to its performance limiting factors is very rare at any performance range.

      etc etc..

  2. Great article as always Andy, just curious on your thoughts / knowledge / experience with assessing ones hydration via the frequency of urinating during an ultra? Is urination purely a way of expelling excess fluids / waste? Is it ideal to be able to maintain a level of “hydration” that requires occasional urination during a race? Does urination enable the body to expel ‘toxic” waste that is detrimental to athletic performance? I have experienced firsthand the effects of hydrating too much during the GNW100 in 2008 when a lack of knowledge led me to consuming 1ltr – 1.2ltr per hour, every hour wether I needed it or not. At the finish I felt like the Michelin man! I was lucky I was only competing in the 100km event as I am certain hyponatremia would have bitten me hard if I had continued. After a 5 year “sabbatical” away from the sport (enjoying food & beer way to much) I have just recently completed the Hume & Hovel 50, where it got quite warm and humid in the midday sun and considering I’m still carrying 8-10kg more than I would like to be I really felt the difference by reducing my fluids to a “as need” level, which on average probably worked out at 500-600ml per hour. I felt consistent throughout the race and dehydration effects were not experienced and I even had the ability to urinate about 3 times during the race. This leads me to seriously consider your views on cramping and where as in the past I would suffer a lot from hamstring and groin cramps (no matter the amount of sodium I would take). I can look back with the joys of hindsight and draw the conclusion that the cramps may in fact have been more associated with poor muscle conditioning and associated poor training. During my “comeback” phase this year I have paid particular attention to training smarter and doing a very regular “Active Isolated Stretching” regime coupled with a low sodium diet, solid hill / tempo work and regular LSD’s and this approach has served me well with cramping being a thing of the past (so far) Is there now a market for just a glucose based sports drink without all the sodium?

    1. Thanks for your comments Dave – Urination is a little more complex than simply a function of hydration – the kidneys, blood sodium levels and the arginie vasopression/anti diuretic hormone all have a big role to play. But if you are frequently urinating then its likely something is going wrong . From a simplistic point of view – sitting at your desk all day and keeping normal hydration levels you might urinate once every few hours , so if you are exercising in hot conditions and sweating loss and urinating more than usual then I would suggest something is not quite right. In my first ultra the last 15 miles or so I must have urinated every 10 times – something clearly not working well, in hind sight probably too much water and an excess of sodium. Hyponatremia is often caused in people who have a syndrome of inappropriate ADH secretion – which is why some people can overdrink and get away with it others cant. In all cases drinking to thirst and not overdrinking will stop the problem from happening

      There are some sports drinks out there with no electrolytes – Hammer Perpetuem is one I know of .

      Cramp can almost always be solved by specific training, tapering properly for a race and pacing the first half of the race well , if you stuff it up then a swill of very salty drink in the mouth should sort any cramps out should they occur

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