Belonging in the same category as “Repeatedly Banging Your Head Against a Brick Wall Can Cause Headaches” is the report “Excess cola can cause super-sized muscle trouble“. Briefly, the article describes a paper soon to be published from Greece which reports two patients who developed hypokalemia associated with drinking huge amounts of cola soft drinks. Forsaking false modesty, let me start by stating that I know as much about hypokalemia as anybody in the world.

One of the effects of hypokalemia (the word just means low blood potassium) is muscle weakness or muscle injury. Both the patients described by the Greek doctors imbibed prodigious amounts of cola – three to nine liters a day. Nine liters is about 2 gallons. They apparently did this for long periods.

Cola contains, among other things, sugar and caffeine. Sugar (glucose and fructose) stimulates insulin release which drives potassium into cells. Caffeine is a weak beta agonist which also drives potassium into cells. Colas are mainly water which is excreted by the kidney. High rates of flow of tubular urine along the distal nephron will increase urinary potassium excretion. And if you’re drinking so much cola you’re likely on a diet low in potassium. Combine all these effects for a long time and hypokalemia severe enough to be symptomatic may result. But you’d have to drink a lot more cola than most sane people would do for a very long time to be at risk for hypokalemia.

The potential difference across a muscle cell is a function of the ratio of extracellular to intracellular potassium. As most of the potassium in the body is inside the cell small changes in extracellular potassium can have a marked effect on this ratio and hence on muscle PD. This is why a sudden shift of potassium into the cell can cause weakness or even paralysis. Hypokalemic periodic paralysis is a classic example of this phenomenon. Hyperthyroidism is the commonest cause of this uncommon syndrome.

Cola consumption is almost certain to be a less common cause of hypokalemia than licorice ingestion which in turn is less common than hypokalemic periodic paralysis. You probably didn’t know about licorice. You’re on your own with this one. If you just can’t contain your curiosity ask me and I’ll tell you about licorice and hypokalemia.

One of the two patients was said to be vomiting. Vomiting itself is a well known cause of hypokalemia. So I can’t be sure that this patient’s hypokalemia was related alone or in part to the consumption of cola.

If you do anything to excess, bad things often happen. Drinking too much water may cause hyponatremia (low blood sodium) also known as water intoxication. I’d worry more about the calories from soda than I would about the remote chance of hypokalemia. There are about 3600 calories in nine liters of cola. Drink diet cola if you like the taste. Excess of diet cola would likely cause water intoxication before hypokalemia.

Don’t worry yourself breathless about rare manifestations of bizarre behavior, there’s enough common stuff that’s sufficiently scary without focusing on the semi-imaginary.

There’s a good review on hypokalemia in the 5 May 2009 issue of the Annals of Internal Medicine: Narrative Review: Evolving Concepts in Potassium Homeostasis and Hypokalemia.

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