I have a huge interest in the science behind endurance racing . I am a gastroenterology Nurse Practitioner, that has been in practice for 10 years , I also have a bachelors degree in exercise science and minor in nutrition . I started realizing I was getting advice from other athletes that prompted a lot if question for myself as person of science and for one whom practices medicine and needs to give sound advise to my patients and as I take on this extreme sport of Ironman. I will not claim to be an expert but I promise to pull together the most recent data I can on the subject of sodium balance with exercise.
This question interested me because so many athletes were advising the use of sodium tablets during endurance racing to my husband and I in order to decrease muscle cramping and aid hydration.
Here is what I found from my research and know from pure physiology. My references are medical journals and Up to Date , which is a data base we use in our clinic to keep us up with the latest data in medical practice.
One point to make is , what is muscle cramping??? Is it due to lack of oxygen or due to sodium depletion. This may be another subject all together. But the point is there is a very common condition and even a medical acronym already defined for a "stitch in your side". It is called ETAP, or Exercise-related Transient Abdominal Pain. It is caused by shunting of blood away from the arteries feeding diaphragmatic muscles , causing a diaphragmatic ischemia ( or lack of oxygen). It presents as pain all across / or tranversing the top of the abdomen, from under the right ribs to the left ribs , or some variation. It appears it is more prevalent in female athletes and sometimes worse with menstruation. It goes away with rest and rehydration and there doesn't appear to be any permanent damage. It is not from low sodium , but key point , is dehydration. Dehydration is different from sodium or electrolyte in-balance.
So what is hyponatremia in the medical sense . Simply low sodium. Why is it bad? Appropriate sodium levels are necessary for acid base balance, water balance, nerve transmission and muscle contraction. When it is low, it is a lower concentration in the blood, due to dehydration ( from excess exercise), or vomiting, and diarrhea. It can be caused by OVERHYDRATION as well. It is rare in healthy individuals with normal kidney function all together.
Next point, Hypernatremia , or excess sodium in the blood in also bad. It can cause permanent neurological damage. Higher then normal sodium can be from too infrequent urination, profuse sweating, or diarrhea or other medical disorders.
Signs and Symptoms of low sodium can be change in mentation or confusion , lethargy, nausea, cramping, twitching, and worse case seizures or coma. The most noticeable symptom for me in practice has been the change in mentation and lethargy. Patients will literally be closing there eyes to sleep while you are trying to talk with them. Pretty extreme. And most of these patients are elderly with poor kidney function , and more than likely on heart medications and diuretics.
Another key point in this discussion about salted verses unsalted. The American College of Sports Medicine tried to put together a task force to come up with a guideline for sodium intake in endurance events and couldn't. Why , because most of us doing these sports, 1. have adequate kidney function to keep this from happening. 2. get enough sodium from our diets alone to keep this from happening, and 3. It cant happen until you become dehydrated. So, there's the answer stay hydrated and it probably wont happen.
Another myth. Most sports drinks with their limited electrolyte's are hypotonic and therefore aren't enough to actually balance an extreme case of hyponatremia. You can drink them. They are good and tasty, and may help in small increments.
Hydration:
DO NOT over hydrate. American College of Sports Medicine, task force on the subject showed that OVER hydration was the number one reason for hyponatremia. They studied Boston Marathon runners, some had a theory to drink as much water as possible during the event , others drank modestly during the event. The ones whom tried to hydrate as much as possible were more apt to be the hyponatremic ones. When one overhydrates and the kidneys are failing to excrete, then the retained fluid may lead to lower sodium levels. Athletes that weighed more across the finish line, were more apt to have low sodium. A sign to look for is darkening urine.
ACSM is saying that hydration of 500 to 1500 liters of water per hour of exercise with a normal diet with normal sodium levels should keep the majority of athletes healthy.
If you are one that seems to get a lot of symptoms with extreme exercise then I would advise a physical with your Doctor.
In the practice of medicine I was taught the horse before the zebra. Meaning most things have the simplest explanation, BUT you cannot forget the zebra exists.
My take home message for myself after all this is :
Eat some potato chips, drink modest amounts of fluids, and as long as I continue to pee every couple hours , its all good. :)
I found an article the link is that talks more on this issue.
http://www.medscape.com/viewarticle/718774
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