by Bob Albright, D.O.

No, this will not be a baseball article or a non-paleo diet breakfast product endorsement. I will try to put potassium’s (K’s) role in muscular function and general health into perspective, and help us with relating its role in our health and athletic performance. Most of us have heard of potassium, equating it with bananas and orange juice and-- for murder mystery buffs -- the perfect crime.

Potassium is the major ion which resides inside our cells. It is the intracellular equivalent of sodium, and we know what havoc changes in sodium can lead to when it’s deranged. Potassium has relatively diminutive concentrations in our bloodstreams, generally accepted levels are between 3.4-5.0 mEq/L. Its role generally is to assist in maintenance of membrane electrical potential -- critical for cellular enzyme, membrane channel, pump and organelle (cellular machinery) function. Additionally, potassium concentration is directly related to acid base and glucose balance. When potassium values are abnormal it suggests a serious issue with abnormal metabolism or poor kidney function (yup, it always comes back to the kidneys with me).

Both low and high potassium levels have been associated with muscle weakness and cramping. Can potassium levels explain the cramping phenomenon many endurance athletes experience? Short answer, probably not.

Several studies have evaluated healthy marathon runners, ironman distance triathletes, sprinters and well-trained cyclists and found no relationship with serum potassium concentrations and the cramping phenomenon. However, among patients whose medications may lead to changes in potassium pre-exertion, cramping and weakness (particularly for low potassium levels --hypokalemia) has been widely reported.

Medications which may lead to potassium levels being lowered include commonly prescribed diuretics and rarely asthma medications (generally a brief phenomenon). Rare kidney diseases which lead to excretion of abnormally high amounts of potassium in the urine can lead to hypokalemia as well. Finally, a rare genetic predisposition to develop hypokalemia following intake of large amounts of carbohydrates has been reported among those of Asian descent. In addition to weakness and cramping, heart rhythm disturbances increase under the influence of hypokalemia (low K). These are potentially serious concerns for endurance athletes.

Fortunately, disorders leading to dangerously elevated levels of potassium are relatively much less common. Kidney dysfunction (particularly in association with diabetes mellitus) is generally a prerequisite for abnormally high potassium levels (hyperkalemia). It is well recognized that exercise itself leads to slight increases in potassium concentrations. This is due to shifting of potassium into the serum as acids are buffered by cells (hydrogen into cells = potassium out). Some physiologists relate higher potassium levels as a trigger for increase in minute ventilation (more oxygen and CO2 exchange by the lungs).

When potassium levels rise quickly to dangerous levels (>~ 6.5 mEq/L), cardiac standstill can result. Life-threatening hyperkalemia among endurance athletes is nearly universally associated with either traumatic or heat-associated muscle tissue breakdown (rhabdomyolysis). Muscle inflammation (and rarely even rhabdomyolysis) associated with statin drug use (for cholesterol lowering) has been reported among endurance athletes as well. Certain antihypertensive drugs, when administered to those with poor kidney function, may lead to high potassium as well. These drugs: ACE inhibitors, angiotensin inhibitor agents, perhaps betablockers and certainly potassium sparing diuretics are all well known to cause increased potassium levels.

Non-steroidal anti-inflammatory drugs (NSAIDS, such as ibuprophen) impair the kidney’s ability to excrete the potassium load -- in addition to fostering low sodium levels (hyponatremia), so, yet another reason to avoid them.

A healthy endurance athlete is unlikely to ever have issues with their potassium. Unexplained muscular cramping is rarely explained by potassium disorders (but might be best checked once), but if you are being treated for hypertension, hyperlipidemia (cholesterol too high), kidney dysfunction or heavily use NSAIDS, it is wise to let your physician know of your endurance athletic pursuits, so he or she can test your potassium. Keep your coaches informed on your medication history as well; they can often spot danger signs that you may overlook.

Got it?

O-K.