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Sodium vs. Potassium

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10/18/02 

I received an email from a fellow forumite asking a couple of questions re the value of sodium and potassium in avoiding cramps during a marathon....and the importance of "pre-loading" either or both before the marathon. Her questions were prompted by a discussion that occurred on this forum in May while I was traveling home from our winter cruise, so I missed it. I used the forum search engine to find the original thread. It seems that Daffy Duck challenged suggestions that I made in a couple of "old" posts.....namely, "Marathon Cramps" and "Pre-race Comments for Marathoners" (both which can be found on my Running Page)....concerning potassium loading before a marathon. Daffy called my suggestion "crap". It looks like StephenK did a good job of "defending" me during my absence. :-) However, since it was my earlier posts that were challenged by Daffy, I would like to add my own comments on the subject here on the forum. If you have no interest in this subject, I strongly suggest that you move on. Otherwise, settle back and get comfortable because this is going to be really long. ;-) BTW, all of the bold emphasis in quotes in this post are mine, not the original authors'.

For two years I have listened to Daffy promote his sodium theme (he calls it salt, but "salts" actually include sodium, potassium, calcium, magnesium and phosphate) every time the subject of cramps comes up and I mention potassium. I have disagreed with what he has been saying. However, I have refrained from challenging him simply because his recommendations were doing no harm. However, it looks like the time has come to speak up.

First, let me say that Daffy has made some valid points, both in the discussion with Stephen and in his prior posts, concerning the value of sodium in a diet. However, most of his points have little relevance to a marathoner.....or anyone else but the chronically ill. A couple of them are simply wrong. And, most of the references he uses to support his comments come from internet sources that are designed for guidance to the "average" person and/or the medically infirm, not marathoners.

(1) Daffy said, "There are no RDA values established for potassium. There is too much potassium in a regular diet."

The first part of this is true....but it's misleading. As Stephen said, the U.S. Government has replaced RDA with DRV and established a recommend DRV for potassium (3500mg/day) and sodium (2400mg/day), based on a diet of 2000 calories/day. That implies that the human body uses or loses more potassium than sodium and requires more on a daily basis to maintain adequate stores. However, marathoners probably require even more than the DRV because of the work their training involves. Maybe, 10-25% more than the DRV would be more realistic. Applying these guidelines, marathoners should be looking to consume "adjusted DRV's" of 3850-4400mg/day of potassium and 2650-3000mg/day of sodium.

The second part of Daffy's statement is ridiculous. What is a "regular diet"? Who eats it? And who measures it? One of Daffy's own references says, "The intake of potassium in the U.S. is usually between 0.8 and 1.5 grams per 1000 calories consumed." That's 1600-3000mg/day for a 2000 calorie/day diet, which is less than the U.S. Government DRV. On that basis, a marathoner would have to eat 3000-5000 calories/day just to ingest the adjusted DRV level of potassium. Of course, most serious marathoners eat a better diet than the average American. Thus, they are probably getting more potassium/1000 calories than the average American, so the picture isn't really that bad, but it hardly means that there is "too much potassium in a regular diet". Actually, it's sodium, not potassium, that is overabundant in most people's diet.

(2) Daffy said, "Too much potassium can be fatal."

That's true. However, according to one of Daffy's own references, "Dietary intake of potassium in excess of 18,000 milligrams can cause high concentrations of the element in the blood, disturbances in heart and kidney function, and alterations in fluid balance." Yep, that would certainly be harmful, maybe even fatal. However, according to (1) above, 18,000 mg of intake would require eating 12,000-22,000 calories!!!!!! Further, according to one of Daffy's references, fatalities due to excess potassium (hyperkalemia) result not from ingesting too much potassium, but from kidney failure, the use of drugs that block the kidneys' excretion of potassium, Addison's disease, severe tissue damage (crush injuries), burn injuries, and crack cocaine overdoses.....none of which rank high on a marathoners risk list. A greater risk for marathoners than hyperkalemia is hypokalemia....low potassium levels, which Daffy's referenced site says, "can cause muscle weakness, twitches, and even paralysis"....or cramps????

As Stephen pointed out, it is also possible to OD on sodium. However, the probability is about as great as OD'ing on potassium. In other words, it's nothing for marathoners to worry about.

(3) Daffy said, "Banana? Banana's don't count as a high potassium food!"

Thanks, Daffy. That's a revelation! Maybe someone should notify Glover, Daniels, Noakes and all the other running gurus, plus all the medical experts and nutritionists, who list bananas at or near the top of the list when talking about good sources of potassium. ;-) Heck, even Daffy's own "expert" references included bananas near the top of their recommended lists.

It is true that there are food sources that are higher in potassium than bananas. Daffy listed a few. But, who wants to eat a couple of avocados each day....especially with their high fat content? Potatoes with skins? I thought marathoners ate them regularly, anyway, and that we were talking about "extras". Feel like pulling out a baked potato for a between meal snack while sitting at your desk or walking down the street? And, extra servings of beans for potassium loading?? Come on. Most marathoners already get enough "boost" from their normal diet. :-)

Actually, Daffy did mention another excellent potassium source that is a convenient and tasty "nibble" food....raisins. And, his referenced link (http://www.krispin.com/potassm.html) listed a few other very tasty dried fruit sources....dates, peaches and prunes.

However, the bottom line is that bananas will remain a favorite among marathoners because they aren't far behind the very top rankers in potassium; are convenient for most people to eat a couple/day; and they are very tasty to most people.

(4) Concerning my comments re using a potassium supplement for 5-6 days before a marathon, Daffy said, "Sorry, I don't agree with the above...at one time I did and went out in search of potassium supplements...when all I could find was a measly 100mg." and "I had gotten sucked into the same fairytale a couple of years ago (from reading this forum!)...I went to a Safeway, Giant Foods and a CVS looking for high potassium supplements...boy did I feel silly."

Daffy seems to have gotten the impression that I was promoting supplements as the primary way to "potassium load" and went looking for a supplement for that purpose.....it's no wonder he felt "silly". That isn't the case. In my "Pre-Race Comments for Marathoners" post, I emphasized potassium loading through diet and mentioned the supplements as an after thought. Because the supplements are limited by law to low dosage, they are simply extra insurance....the icing on the cake....topping off the tank. They certainly are not the main source of potassium when preparing for a marathon. They probably aren't even necessary, if one's diet includes a lot of potassium during the week before the marathon. But, because of their low dosage, they don't hurt....and just might help a little after mile 21 in the race.

I could go on, but enough of this "defensive" BS. So far, none of the rhetoric expounded by Daffy, Stephen and me address the real issue.....do potassium and/or sodium play a role in helping to avoid marathon cramps? If so, what is it? Does pre-race potassium and/or sodium loading benefit a marathoner? If so, how? Well, I certainly don't claim to conclusively know the answers to these questions. From what I have read, none of us one do. If we did, we wouldn't be having this discussion.

The running experts (Glover, Noakes, et al.), as well as the medical and nutritional sources referenced by Daffy, Stephen and me, are all careful to say that there have been no conclusive studies that demonstrate that either potassium or sodium plays a significant role in avoiding cramps. Of course, the corollary to that is that there have been no conclusive studies that demonstrate that potassium and/or sodium don't play a helpful role in cramp avoidance. In the absence of conclusive scientific studies, I prefer to rely on logic and anecdotal evidence.

Most running, medical and nutritional "experts" that I have read all say that a shortage of either sodium or potassium results in muscle fatigue. And, most running "experts" say that muscle fatigue is a primary cause of marathon leg cramps. I think the combination of these two points indicates that a shortage of sodium or potassium during a marathon can indirectly result in muscle cramps. An analogy, albeit a poor one, is the classic argument about whether guns or people kill....people certainly pull the trigger, but the gun is still called the "murder weapon." In my simple mind, "gun"=electrolytes and "people"=muscle cramps.

Anecdotally, I found that my problems with marathon cramps stopped after my first 4 marathons when I started "potassium loading" during my taper. Of course, I also had a stronger base and was training harder at that point. So, how significant was the addition of potassium loading vs. the other factors? I don't know for certain, but I wasn't about to stop potassium loading to find out. :-) I had found a cramp avoidance "recipe" that worked for me and wasn't about to alter it. As further anecdotal evidence, several forumites have told me that their problem with marathon cramps stopped when they followed my suggestion of potassium loading.

StephenK referenced an excellent technical article by Dr. Bill Misner on a website called "Integrated Sports Solutions" that comes the closest I have seen to authoritatively associating electrolytes, including sodium and potassium, to cramps during an endurance sport effort. In it he says the following:

'Some have assumed that exertional cramping may be the result of fluid electrolyte improprieties. Modern research science is divided on the importance of sweat losses of sodium, chloride, potassium, and magnesium and regards them as trivial, therefore not evidential as a primary cause of the "Rigor Complex". (Maughn 1986, Miles & Clarkson 1994) Chaudry(1982), however, added an interesting footnote from his unpublished observations," There is some preliminary evidence which indicates that ATP translocation is associated with sodium, potassium, -ATP-ase."'

'The Cations and Anions of fluid electrolyte composition are never static, but are proportionately balanced within the compensatory rates of metabolic activity both intracellularly and extracellularly. Pivotal losses of calcium and magnesium from muscle exhaustion, fluid dehydration from sweat loss, depletion of extracellular cation stores of sodium or intracellular cation stores of potassium are significant factors staged for muscle failure, I.E., a cramp event. While the previously mentioned case study of a nationally-ranked tennis player whose severe exertional muscle cramps were solved by dietary sodium supplementation, modern science considers one solution insignificant in terms of scientific methodology for settling on conclusive evidence. Muscle cramps have been associated with a hypokalemic tissue environment, and were readily relieved by potassium supplements.(Portier 1973) Glatzel(1980) was successful treating nocturnal cramps with dietary sodium chloride. Strong evidence exists for the role of electrolyte depletion associated with muscle spasms, cramps, and seizures, but inconclusive from present research literature. In fact, depletion of muscle glycogen, fluid overhydration, and the lack of vitamin substrates with enzymatic influence on fuel selection are also presently considered suspects.'

and:

'CONCLUSIONS: WHAT MAY CAUSE MOST EXERTIONAL MUSCLE CRAMPS!

'Depletion of the immediate and most easily converted fuels for ATP conversion(Carbohydrate stores:muscle glycogen & blood glucose) may prompt a temporary deficiency which results in muscle failure or "Rigor Complex". Similar deficiencies in calcium spent during extreme exercise may further trigger imbalances in its ideal ratio of 2:1 to magnesium associated with muscle spasms and cramping. Too much or too little tissue fluid volume affect the working ratios of intracellular potassium to extracellular sodium, which also affects substrate anion stores in both. For example, exertional dehydration and electrolyte sweat loss per hour are as follows: (Electrolyte per volume of fluid)Sodium=2grams/liter, Chloride=1gram/liter, Potassium=0.2gram/liter, Magnesium=0.1gram/liter. While these electrolyte losses are trivial, depletion levels after 3 hours are significant, resulting in inefficient muscle contraction, spasms, or cramps in athletes who have not conditioned themselves to endure such deficiencies.'

Dr. Milner's comments indicate that sodium is lost through sweat during an endurance effort at a rate that is 10 times the rate of potassium loss. That would tend to support Daffy's assertion that the marathoner's focus should be on loading sodium, not potassium, right? Well, no, just the opposite is the case. Why is that? To answer that question, I'll refer to "The Lore of Running", by Dr. Timothy Noakes, physician, physiologist and accomplished runner with 70 marathons and ultras to his credit. Rather than paraphrase what Dr. Noakes said about sodium and potassium, I'll offer some quotes directly from his book.

Sodium -

'...the average daily salt intake of the average runner exceeds his or her daily requirement by about 8g and is therefore more than enough to cover the salt requirements of running as much as a marathon per day.....For this reason, one might argue that extra salt is not required when one exercises. However, we now know that the issue is somewhat more complex.

'Calculations suggest that during prolonged exercise the body is forced to deplete its fluid stores as a consequence of the sodium chloride losses in sweat. If this did not occur and if the body fluid stores were allowed to remain normal, then a dilutional hyponatremia with potential catastrophic effects would develop in all runners competing in races lasting more than 4 hours.

'It follows that the only way in which dehydration can be prevented during exercise is to replace both the sodium and water lost through sweat as these losses develop. Runners are not at risk of developing deficiencies of either magnesium or potassium during exercise, thus neither need to be replaced.'

And more on sodium:

'....The total body content of sodium is about 80 g.'

'The daily food intake of persons living on the typical Westernized diet has a sodium chloride content of 5 to 20 g. Of this, 3 g occurs naturally in the food, 3 to 5 g are added during processing, and the rest is added by the consumer.'

'Current evidence shows that the body's daily salt requirement is about 0.2 to 0.5 g, about one tenth of what we actually consume. The excess that is ingested is lost in the urine. Even vigorous and prolonged daily exercise increases salt requirements only very slightly, because sweat has a low-salt content that decreases as one becomes more fit and acclimatized....'

'Interestingly, most of the scientific literature on muscle cramps during exercise in the heat (heat cramps) was written in the 1930s and early 1940s (Dill, 1936; Talbott, 1935; Taylor, 1943); little work has been done subsequently.

'The overriding conclusion (of Dill and Taylor) was that when salt deficiency was induced by very prolonged exercise in the heat in subjects eating severely salt-restricted diets, the predominant symptoms the subjects developed were heat exhaustion with cardiovascular collapse. Muscle cramps were a minor and uncommon feature. Thus, both Dill and Taylor concluded that salt deficiency is only one of many factors explaining heat cramps, whereas Sohar and Adar (1964) concluded that the evidence linking salt deficiency to muscle cramps is tenuous at best. In fact, it seems that most cases of "heat cramps" described in these reports occurred in persons who also drank copious amounts of fluids while exercising in the heat. The cramps may really have been caused by hyponatremia resulting from fluid overload rather than from salt deficiency.'

So, Dr. Noakes says that we get much more salt in our diet than we can possibly use, even during a marathon; the body gets rid of all that we consume in excess of the 80g that we can store, therefore attempts to "sodium load" are futile; and we are not at risk of potassium and magnesium deficiencies in a marathon because their losses are minor. In fact, the only significant problem resulting from electrolyte loss that he talks about is dehydration, nor cramps, resulting from sodium lost in sweat. So, what does all this have to do with potassium loading? Well, read on to see what Dr. Noakes has to say about potassium:

Potassium -

'Potassium is stored in the body mainly inside cells and is found in citrus fruits, bananas, and tomatoes. The daily potassium requirement is about 2 to 4 g, which is about 4 to 8 times more than the daily salt requirement. The total body potassium store is also about 90 g.

'During exercise, potassium is lost in urine and sweat, but these losses are trivial. Thus, the sweat potassium content is only 0.1 to 0.2 g/l; even when eating a low-potassium diet (2 g/day), subjects exercising at 50% VO2max for 2 hours a day in the heat showed no evidence of developing potassium deficiency.

'The major factor for runners is that potassium is stored with glycogen in the body; hence, potassium requirements are increased during carbohydrate loading. The ingestion of fruit during carbohydrate loading will adequately cover the additional potassium needs.

'The potassium stored with glycogen is released into the bloodstream as exercise progresses and as intramuscular glycogen stores are utilized. The extra potassium is then lost in sweat and urine in place of sodium chloride; thus, potassium excretion during exercise helps to conserve sodium.'

So, there you have it. According to Noakes, the benefit of potassium loading is to stock up on extra stores in the muscles so they can play a sacrificial role to conserve sodium, the loss of which drains water form the body and contributes to dehydration. Unlike Dr. Milner, Dr. Noakes doesn't suggest that sodium or potassium depletion during a marathon directly causes muscle cramps. However, both acknowledge that the balance of water and electrolytes is important in avoiding cramps. Noakes emphasizes excess water consumption, as opposed to sodium depletion, as the primary cause of cramps that result from hyponatremia. However, his statements were carefully related to the results of specific studies that he could identify. I would think that the two factors go hand in hand, as Milner suggests.

Bottom line to all of this is that, as I said in the beginning, there are no absolutely conclusive answers. Not enough controlled scientific research has been done to arrive at any. Meanwhile, Daffy will continue to believe that my suggestion to "potassium load" during the taper is "crap"; and I will continue to believe that his beating the sodium drum is....well....daffy. ;-) Each marathoner has to read and listen to all the info s/he can find on the subject and decide what makes sense to him/her.

If you made all the way through this tome and are still awake, congratulations and get a life!! :-)

Jim2