Nutrition Basics: Powerful Potassium


Potassium is the 3rd most abundant mineral in the body behind calcium and phosphorus, which makes it really important. (Not that the other micronutrients aren’t also important. I’m not showing any favorites here!)

There is a lot of information here and it can be kind of confusing because some of the symptoms for too much potassium are the same as for too little potassium. So I want to highlight what I consider to be the most widely relevant points about potassium:

  1. Processed food has been stripped of most of the potassium that was in it. So if you aren’t eating lots of vegetables, fruits, legumes, nuts and seeds, you might be deficient.
  2. Too little potassium can cause high blood pressure, muscle weakness and general fatigue, in addition to muscle cramps.
  3. Bananas are not the best source of potassium. (Surprise!)

Now, if you are so inclined, read on for the full story…

Functions in the body

Almost all (95 – 98%)  of the potassium in the body is found inside cells, making it the major cation in the intracellular fluid. Just for clarity, “cation” is a scientific term meaning that the atom carries a positive charge when it is in water.

Perhaps its most important role is as the counterbalance to sodium, which is the major cation in the extracellular fluid. Just like sodium helps control the fluid in the blood vessels (i.e., outside the cell), potassium helps control the fluid level inside the cells by drawing water and nutrients into the cells. This means the interaction between sodium and potassium helps to maintain osmotic pressure which is the balance of fluid inside and outside the cells.

Also, because it has a positive charge (like most of the minerals), it:

  • Is a major player in maintaining pH balance within the cells,
  • Influences the excitability of nerves, which means it helps with the conduction of messages throughout the nervous system, and
  • Affects the contraction of:
    • Smooth muscles (found in organs like the intestines, bladder and uterus),
    • Skeletal muscles (what you normally think of when you think of muscles like your biceps and quads), and
    • Cardiac muscle.

Causes of deficiency

Although deficiency is not considered common because potassium is so abundant in real, whole foods, many people are deficient because of how much processed food we tend to eat. As well, deficiency occurs with an unbalanced diet that doesn’t include enough fruits, vegetables, nuts, seeds and legumes. (How many people do you know who get the recommended 6 – 11 servings of produce every day?)

The ingestion of clay (bentonite) or chronic laxative use can result in potassium not being absorbed, even if sufficient amounts are ingested in food. As well, kidney conditions that increase the excretion of potassium can result in insufficient levels.

Anything that causes dehydration can result in too little potassium in the blood. These situations include chronic vomiting, chronic diarrhea and/or use of diuretics that do not spare potassium.

Finally, anything that causes a massive shift of potassium out of the blood and into the cells can result in too little potassium being in the blood. These situations can include a large dose of insulin, refeeding syndrome (typically occurs when enteral or parenteral nutrition is administered at a high rate following an extended period of starvation or malnutrition), too much stimulation of the sympathetic nervous system (a side effect of some medications) and familial periodic paralysis.

Symptoms of deficiency

Symptoms of deficiency don’t often show up with mild deficiency. As well, symptoms are non-specific, meaning they aren’t just related to potassium levels, and can’t be confirmed to be caused by low potassium without a blood test. That being said, knowing what the symptoms are can help identify low potassium as a possible problem. Symptoms include (with the most common in bold):

  • Muscle weakness, cramps or pain
  • Fatigue
  • Hypertension (sometimes the problem is not excess sodium so much as it is insufficient potassium… remember it’s the balance that’s important.)
  • Hypotension (yes, that’s confusing; remember it’s about the balance with sodium and magnesium)
  • Impaired glucose tolerance or worsening diabetes control (which may be characterized by more frequent urination)
  • Calcium loss from bone and/or increased calcium in the urine
  • Edema or swelling of the extremities (again, it’s about the balance with the extracellular minerals)
  • Kidney stones
  • Confusion, irritability or depression
  • Respiratory failure or low respiratory rate
  • Paralysis
  • Death

Causes of toxicity

The most common cause of hyperkalemia is kidney dysfunction, such as that seen in chronic kidney disease, because this prevents potassium from being excreted in the urine. Other causes include:

  • Insulin dependent diabetes mellitus or insulin resistance (because insulin helps move potassium out of the blood and into the cells)
  • Low adrenal function, adrenal fatigue or Addison’s disease
  • Massive tissue destruction as may be seen with excessive alcohol use, severe injury or burns (the potassium is released out of the cells and into the bloodstream)
  • Cancer
  • Chronic diarrhea or other causes of metabolic acidosis
  • Use of certain medications including potassium sparing diuretics (so the potassium is not sufficiently excreted), ACE inhibitors, NSAIDs (like ibuprofen and aspirin), anticoagulants, angiotensin receptor blockers (ARBs), beta-blockers, cox-2 inhibitors, cyclosporine, anti-fungal medicines
  • Very low sodium diets (because of the way sodium balances potassium and keeps it inside the cells)

Symptoms of toxicity

Even though toxicity is not common because potassium can be excreted in the urine, the outcomes can be dire! The body works hard to maintain the serum potassium level in a very tight range (ideally 3.5 – 4.5 mEq/L), and when it gets out of that range the heart is impacted. In its mildest form hyperkalemia (i.e., abnormally high serum potassium concentration) can cause heart arrhythmia, nausea, muscle weakness and fatigue, but at its worst it can cause a heart attack or simply stop the heart.

Measuring levels

The most common way of measuring potassium is in the blood because of how important it is in maintaining a normal heart beat. However, this isn’t a great assessment of the potassium inside cells because, as mentioned with magnesium, the body maintains blood mineral levels to the detriment of minerals inside cells.

Measuring the potassium inside red blood cells is a good indicator of intracellular levels, which is where most of it is kept as mentioned above.

Using a “whole blood” measurement gives a picture of potassium status  throughout the body because it measures what’s in the serum along with what’s inside the red blood cells. This is the most complete picture of potassium status.

Sources of Potassium

Although we almost always think of bananas when someone mentions potassium, it occurs naturally in lots of foods including numerous vegetables, fruits, legumes, nuts and seeds.

As well, bananas are not the most abundant source. For example, one medium banana has 422 mg of potassium while one cup of Swiss chard has 961 mg.

These are the foods that are great sources (i.e., they have at least 10% of the Daily Value) and can be consumed to ensure you’re getting enough potassium:

  • Greens, especially beet greens, spinach, bok choy, Swiss chard, kale, turnip greens and Romaine lettuce
  • Legumes, especially Lima beans, soybeans, pinto beans, lentils and kidney beans
  • Potatoes (all kinds)
  • Avocado
  • Tuna
  • Beets
  • Papaya
  • Brussels sprouts
  • Squash (both winter and summer)
  • Salmon
  • Broccoli
  • Cantaloupe
  • Tomatoes
  • Banana (of course)
  • Asparagus
  • Cabbage
  • Carrots
  • Green peas
  • Fennel
  • Scallops
  • Onions


— Allen S. Assessing Traditional Labs from a Functional Medicine Perspective Part 2: CMC and other Important Analytes. Lecture slides.
— Gropper SS, Smith JL. Advanced Nutrition and Human Metabolism. 6th ed. Belmont, CA: Wadsworth Cengage Learning; 2013.
— Lewis JL. Hypokalemia. In Eletrolyte Disorders. Accessed on April 21, 2015.
— Lord RS, Bralley JA. Laboratory evaluations for integrative and functional medicine. Metametrix Institute; 2008.
— The World’s Healthiest Foods. Potassium. Accessed on April 20, 2015.

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