Potassium
Synonym: potassium

Characteristics: It is the most abundant intracellular (intracellular) cation, which occurs naturally in many foods and is also available as a dietary supplement. Potassium is present in all body tissues and is essential for normal cell function as it plays a role in maintaining intracellular fluid volume and transmembrane electrochemical gradients. Potassium has a strong relationship with sodium, the main regulator of extracellular (extracellular) fluid volume, including plasma volume. The intracellular concentration of potassium is about 30 times higher than the extracellular concentration, and this difference is made up of a transmembrane electrochemical gradient that is maintained via the sodium-potassium (Na+/K+) ATPase transporter. In addition to maintaining cellular tonicity (tension), this gradient is essential for proper nerve transmission, muscle contraction, and kidney function.

Absorption: Potassium is absorbed by passive diffusion mainly in the small intestine. About 90% of ingested potassium is absorbed and used to maintain its normal intracellular and extracellular concentrations. Potassium is mainly excreted in the urine, some in the stool, and a very small amount is lost in sweat. The kidneys control potassium excretion in response to dietary changes, and potassium excretion rises rapidly in healthy people after potassium consumption unless body stores are depleted. At least 195 mg of potassium is excreted daily in the urine. This, combined with other obligatory losses, suggests that potassium balance cannot be achieved with intakes below 400–800 mg/day.

Dietary supplements: In dietary supplements, potassium is often present as potassium chloride, but many other forms are also used – including potassium citrate, phosphate, aspartate, bicarbonate, and gluconate. Humans absorb about 94% of potassium gluconate, and this absorption rate is similar to potassium from potatoes. Some dietary supplements contain potassium iodide in microgram amounts, but this compound serves as a source of iodine, not potassium. Dietary supplements usually provide around 80 mg of potassium. Many manufacturers of dietary supplements limit the amount of potassium in their products to 99 mg due to concerns that intake of higher amounts may be associated with the development of lesions of the small intestine.

Natural sources: Potassium is found in a wide range of plant and animal foods and in beverages (coffee, tea). It is estimated that the body absorbs about 85-90% of potassium from food. Fruits and vegetables (potatoes) are excellent sources, as are some legumes (e.g. soybeans). Forms of potassium in fruits and vegetables include potassium phosphate, sulfate, citrate, and others, but not potassium chloride (the form used in salt substitutes and some dietary supplements). Potassium is also found in meat, poultry, fish, milk, yogurt, and nuts. Among starchy foods, whole wheat flour and brown rice are much higher in potassium than their refined counterparts, white wheat flour and white rice.
Effect: According to an extensive body of literature, low potassium intake increases the risk of hypertension, especially when combined with high sodium intake. Higher potassium intake, on the other hand, can help lower blood pressure, in part by increasing vasodilation (widening of blood vessels) and urinary sodium excretion. Some research suggests that potassium citrate supplementation reduces the risk of kidney stone formation and growth. Observational studies suggest that increased consumption of potassium from fruits and vegetables is associated with increased bone mineral density, thus may improve bone health. Numerous observational studies of adults have found associations between lower potassium intake and increased fasting glucose, insulin resistance, and diabetes.

Deficiency: Inadequate potassium intake can increase blood pressure, risk of kidney stones, and urinary calcium excretion. Severe potassium deficiency can cause hypokalemia. Mild hypokalemia is characterized by constipation, fatigue, muscle weakness, and malaise. Moderate to severe hypokalemia can cause polyuria (a large volume of dilute urine), encephalopathy in patients with kidney disease, glucose intolerance, muscle paralysis, poor breathing, and cardiac arrhythmias. Severe hypokalemia can be life-threatening because it affects muscle contraction and thus cardiac function. Hypokalemia is rarely caused by low dietary potassium, but may result from diarrhea, laxative abuse, and vomiting. Magnesium depletion may contribute to hypokalemia by increasing urinary potassium losses. Potassium is excreted in the colon and this process is normally balanced by absorption. However, in inflammatory bowel disease (including Crohn's disease and ulcerative colitis), potassium secretion increases, which can lead to potassium deficiency. Inflammatory bowel disease is also characterized by chronic diarrhea, which can further increase potassium excretion. Some diuretics (e.g. thiazide diuretics) commonly used to treat high blood pressure increase urinary potassium excretion and may cause hypokalemia. Large doses of laxatives and repeated enema use can also cause hypokalemia because they increase potassium loss in the stool.

Recommended daily dose: adult: 3400 mg for men, 2600 mg for women (2900 mg during pregnancy, 2800 mg during breastfeeding).

Adverse effects: In healthy people with normal kidney function, high dietary potassium does not pose a health risk (mild gastrointestinal symptoms may occur) because the kidneys excrete excess potassium in the urine. The use of potassium salts in some medications has been associated with lesions of the small intestine that cause obstruction (blockage), bleeding, and perforation (rupture).

Interactions: ACE inhibitors and sartans, which are used to treat hypertension and heart failure, reduce urinary potassium excretion, which can lead to hyperkalemia. Potassium-sparing diuretics such as amiloride and spironolactone reduce urinary potassium excretion and may cause hyperkalemia. Treatment with loop diuretics such as furosemide and thiazide diuretics such as chlorothiazide increases urinary potassium excretion and may lead to hypokalemia. Experts recommend monitoring the potassium status of people taking these medications.

Pregnancy: safe at usual doses.

Breastfeeding: safe at usual doses.

Toxicity: In people with impaired urinary potassium excretion due to chronic kidney disease or the use of certain medications, even dietary potassium intake can cause hyperkalemia. Hyperkalemia can also occur in people with type 1 diabetes, congestive heart failure, adrenal insufficiency, or liver disease. Although hyperkalemia can be asymptomatic, severe cases can cause muscle weakness, paralysis, palpitations, paresthesia (a burning or tingling sensation in the extremities), and cardiac arrhythmias, which can be life-threatening.