Potassium

Potassium (K+) is the principal intracellular cation and the fourth most abundant mineral in the human body. Adult body potassium totals approximately 140-150 g, with over 98% located inside cells. The steep concentration gradient between intracellular (~140 mEq/L) and extracellular (~4 mEq/L) compartments, maintained by the Na+/K+-ATPase, is the fundamental basis for membrane potential, action potential generation, and numerous downstream excitability phenomena.

Biological functions

Potassium's physiological roles include: (1) resting membrane potential — cellular selective permeability to K+ establishes the negative resting voltage of excitable cells; (2) action potential repolarization — voltage-gated potassium channels repolarize depolarized membranes in neurons and cardiac myocytes; (3) cardiac excitability — both hypo- and hyperkalemia produce characteristic ECG changes and arrhythmia risk; (4) acid-base regulation — potassium shifts between intra- and extracellular compartments in exchange with hydrogen ions; (5) insulin secretion — beta-cell ATP-sensitive potassium channels couple glucose sensing to insulin release; (6) blood pressure regulation — potassium modulates vascular smooth muscle tone and renal sodium handling.

Requirements

The 2019 NAM DRI set Adequate Intake for potassium at 3400 mg/day for adult men and 2600 mg/day for adult women, a reduction from the 2005 AI of 4700 mg/day. No Tolerable Upper Intake Level was established because excess potassium is rapidly excreted in individuals with normal renal function. NHANES data indicate median US intake of approximately 2800 mg/day for men and 2200 mg/day for women, meaning approximately 97% of US adults consume below the 2005 AI and ~50-70% below the 2019 AI.

Blood pressure and cardiovascular outcomes

Higher dietary potassium lowers blood pressure, particularly in sodium-sensitive individuals. The DASH trial (Appel et al., NEJM 1997) documented substantial blood pressure reductions with a fruit- and vegetable-rich diet providing approximately 4700 mg potassium/day. Meta-analyses (Aburto et al., BMJ 2013) associate higher potassium intake with reduced stroke (approximately 24% relative reduction) and cardiovascular event risk. The Salt Substitution and Stroke Study (SSaSS, NEJM 2021) showed that replacing sodium chloride with a 75/25 salt-potassium chloride blend reduced stroke by 14% and major cardiovascular events by 13% in a large Chinese trial.

Dietary sources

Per USDA FoodData Central (mg K per serving): baked potato with skin 900, sweet potato 540, white beans (1 cup cooked) 1000, kidney beans (1 cup) 715, lentils (1 cup) 730, banana 420, orange 240, orange juice (8 oz) 450, avocado (1/2 medium) 490, spinach (cooked, 1 cup) 840, beet greens (1 cup) 1300, tomato sauce (1 cup) 810, salmon (3 oz) 370, yogurt (6 oz) 380, milk (8 oz) 370, cantaloupe (1 cup) 430.

Potassium-to-sodium ratio

The ratio of potassium-to-sodium intake may matter more than either in isolation for cardiovascular outcomes. Contemporary US diets average a potassium:sodium molar ratio of approximately 0.5:1, inverted from traditional diets (estimated 4:1 or higher). Increasing potassium-rich foods while reducing sodium-rich processed foods shifts this ratio favorably and produces larger blood pressure effects than either intervention alone.

Disordered potassium states

Hypokalemia (serum K <3.5 mEq/L) typically results from gastrointestinal losses (vomiting, diarrhea, laxative abuse), renal losses (diuretics, hyperaldosteronism, Cushing syndrome), or intracellular shift (insulin administration, beta-agonists, alkalosis). Clinical manifestations include muscle weakness, fatigue, constipation, arrhythmia, and ECG changes. Hyperkalemia (serum K >5.0-5.5 mEq/L) occurs with renal failure, potassium-sparing diuretics, ACE inhibitors, or massive tissue breakdown; severe hyperkalemia is cardiac-arrest risk.

Renal considerations

Patients with chronic kidney disease may require potassium restriction as excretory capacity declines; these patients should not adopt high-potassium dietary patterns without clinical guidance. For healthy individuals, no upper limit on dietary potassium is established, and benefits of higher intake are robust across intervention evidence.