What causes low potassium levels?

If your blood work shows low potassium levels, your doctor will probably want to act. Depending on the situation, they might prescribe oral or IV potassium supplements to get those levels up.

The next step is to determine what’s causing the low potassium levels. According to the medical literature, hypokalemia (low serum potassium) is most commonly caused by gut or renal potassium losses.

These losses are carried out through urine, feces, and vomit. And if the losses are heavy enough, potassium levels can fall below normal ranges.

Kidney issues are a primary driver of potassium losses, but diuretics, laxatives, and various gut problems can also contribute. There are other causes too—like refeeding syndrome, genetic disorders, and PICA (a condition in which the patient will eat inedible things like clay)—but those are the main ones.

You’ll notice I didn’t mention dietary potassium. And you might be wondering: is Robb losing his fastball? Did he miss his morning coffee? Did he accidentally run into a glass door and bang his head? No, no, and maybe—but that’s a story for another time.

I’m not saying dietary potassium is unimportant. Getting enough potassium is crucial for heart health, bone health, and kidney stone prevention. The data is overwhelming on this point. Yet low potassium intakes RARELY cause hypokalemia. The human kidney is simply too good at maintaining potassium levels to let that happen.

Other undesirable things may result... Blood pressure may rise, bones can decompose, kidney stones may form. But blood potassium will be maintained. Serum potassium is your body’s priority. Let me explain why.

The Importance of Potassium

Without potassium, your body wouldn’t be able to use energy. It wouldn’t be able to use ATP (adenosine triphosphate) to power living cells.

We make ATP because ATP powers the sodium-potassium pump. The sodium-potassium pump—which pumps sodium and potassium ions through cell membranes—is the real star. Why? Because pumping these ions allows the cell to stay charged up (like a battery) and conduct nerve impulses. That’s how cells communicate.

I’m glad my cells communicate. It prevents me from devolving into a blob of unorganized biomass. Sometimes I feel like a blob of unorganized biomass after a poor night’s sleep, but even my sleep-deprived cells still work miracles. They still communicate at rates I can’t comprehend.

And they need potassium and sodium to do that. They need the sodium-potassium pump.

The sodium-potassium pump also:

  • Maintains fluid balance inside and outside cells to keep your blood flowing, your eyes moist, and your brain floating in cerebrospinal fluid.
  • Helps transport glucose and amino acids into cells.
  • Regulates brain activity.
  • And much more

That’s why your body works tirelessly to maintain serum potassium levels. Because when potassium levels fall, the engines in all your cells start sputtering. Undesirable symptoms may follow.

Symptoms of Low Potassium Levels

People with mild hypokalemia can be asymptomatic. Alternatively, they might think they’re asymptotic but actually have minor disruptions.

Mild hypokalemia often manifests as low energy, muscle cramps, slight muscle weakness, constipation, fatigue, and malaise. These symptoms look similar to many other conditions—low sodium, low magnesium, Lyme disease, dehydration, etc.—so they can be tricky to spot.

Moderate to severe hypokalemia is easier to spot. The symptoms include:

  • Slower heart rate
  • Muscle paralysis
  • Severe muscle weakness
  • Cardiac arrhythmias
  • Brain damage
  • Glucose intolerance
  • Rhabdomyolysis (kidney-damaging muscle breakdown)
  • Problems with kidney function
  • Polyuria (excessive urine)

In severe cases, hypokalemia can be fatal. That’s why hospitals take it so seriously.

They also take it seriously because it’s so common. About 21% of hospitalized patients have low potassium levels.

It makes sense. Hospitalized patients are more likely to have kidney issues. They’re more likely to take diuretics. And they’re more likely to have loose stools. Let’s talk more about these hypokalemia causes now.

What Causes Low Potassium Levels?

If you have low potassium levels, you’ll want to determine what’s causing them. Here are the main suspects.

#1: Urinary losses

If your kidneys don’t work properly, you won’t retain potassium properly. That’s why renal failure is a leading cause of hypokalemia.

Diuretic drugs also increase urinary potassium losses. These medications largely explain the ubiquity of hypokalemia in hospitals.

Clinicians often order a 24-hour urine collection to test for potassium losses. Hauling around a jug of warm pee isn’t how most of us enjoy spending our Tuesday, but sometimes we just have to deal.

#2: Gut losses

You lose potassium from feces and vomit. This means that any condition that causes diarrhea or vomiting will increase hypokalemia risk.

The list of these conditions includes:

  • Crohn’s disease
  • Ulcerative colitis
  • Irritable bowel syndrome
  • Cholera
  • Gastroenteritis due to bacterial or viral infection
  • Food intolerance or sensitivity
  • And many others

Vomiting can also increase potassium losses indirectly. That’s because losing stomach acid increases your body’s alkalinity, and your body responds by excreting alkaline stuff. (Potassium is an alkaline mineral.)

#3: Increased cellular uptake

Potassium doesn’t just hang out in the serum. It also performs intracellular functions.

But if these transcellular shifts happen too quickly, potassium levels can fall. Here are some factors that suck potassium into cells:

  • High levels of insulin
  • High levels of aldosterone, a hormone released on low sodium diets
  • Alkalemia (high PH)
  • Consuming caffeine
  • Activation of the “fight or flight” sympathetic nervous system

Refeeding after prolonged starvation also pulls potassium into cells to repair malnourished tissues. Unfortunately, this condition (called refeeding syndrome) can cause severe hypokalemia and other electrolyte imbalances.

#4: Poor potassium absorption

Any condition that inhibits potassium absorption is bad news for potassium status. The main culprits are gut disorders like IBD and IBS, but I also want to mention a psychological disorder called PICA.

A patient with PICA will swallow anything in sight: napkins, bricks, dirt, clay, lawn clippings, staples, and other office supplies. Kids usually outgrow PICA, but not always. Anyway, some of these objects may bind to potassium and thereby interfere with its absorption.

#5: Low potassium intakes

A low-potassium diet isn’t a primary cause of hypokalemia, but it’s still worth mentioning. The less potassium you consume, the less of a buffer you’ll have against low potassium levels.

Low Potassium Levels vs. Potassium Deficiency

If your serum potassium looks normal, congrats: you don’t have hypokalemia or hyperkalemia. But you may yet be potassium deficient.

Potassium deficiency doesn’t typically show up in the blood. Why? Because your body is a master at maintaining serum levels.

One way it does so is by shutting down urinary potassium excretion. Another is by pulling potassium from bone to stabilize blood levels. Should we be surprised that low potassium intakes are linked to osteoporosis?

Low potassium intakes are also linked to high blood pressure. Potassium not only dilates blood vessels, but also balances the effects of sodium on bp.

The conventional wisdom is to limit sodium, but that strategy doesn’t work. The science is clear on this. In fact, low sodium diets elevate blood pressure by increasing a sodium-retention hormone called aldosterone.

The trick is to eat adequate potassium AND adequate sodium. Then everything runs as seamlessly as a Swiss bobsled team.

Getting back to the point, don’t look for these deficiencies in the blood. You need to assess your electrolyte status by other means.

How to Get Enough Potassium

A blood test is just one piece of the potassium puzzle. When it looks good, it means your potassium retention system is working properly. The other piece of the puzzle is potassium intake. You want to optimize potassium intake regardless of symptoms or bloodwork. This will reduce the risk of hypertension, osteoporosis, and kidney stones. It will probably also make you feel better.

Aim for the Institute of Medicine’s evidence-based target of 4.7 grams per day. 97% of Americans fall short of this target, so don’t expect to hit it on the first pass. To get enough potassium, start with your diet. Tally up your intake using a food logger like Cronometer, see where you stand, and adjust as needed.

Assuming you are short, begin by eating more potassium-rich foods like spinach, salmon, avocados, and tomatoes. You should easily clear 3 grams this way, and maybe even 4.

To make up the extra gram or two, turn to potassium supplements. To mimic how potassium is normally absorbed, I recommend taking these supplements with food.

You can also consume fluid potassium by adding electrolytes to your water. Do I know any good electrolyte drink mixes with a nice hit of potassium and zero sugar? I do indeed.

Anyways, there’s no downside to getting enough potassium. For a small effort, you get big benefits.