What is the role of potassium in the body?

The Role of Potassium in the Body

Potassium is absolutely essential for life as it is the principal intracellular cation involved in critical physiological processes including nerve impulse transmission, muscle contraction (especially cardiac muscle), and maintenance of normal renal function. 1, 2

Distribution and Homeostasis

• 98% of the body's potassium is contained within cells (intracellular), while only 2% is in the extracellular compartment, making even small shifts potentially dangerous 3, 4
• The normal intracellular concentration is approximately 150-160 mEq/L, while normal plasma concentration is 3.5-5 mEq/L 1
• This gradient is maintained by an active ion transport system across the plasma membrane 1
• Potassium moves rapidly between intracellular and extracellular compartments to maintain normal serum levels 3

Critical Functions of Potassium

• Maintenance of intracellular tonicity and fluid balance 1
• Transmission of nerve impulses throughout the body 1, 2
• Contraction of cardiac, skeletal, and smooth muscle 1, 2
• Participation in carbohydrate utilization and protein synthesis 2
• Regulation of acid-base balance in conjunction with other electrolytes 2
• Maintenance of normal renal function 1

Potassium Balance

• Under normal conditions, potassium intake (typically 50-100 mEq per day) equals the amount excreted in urine 1
• Renal excretion accounts for approximately 90% of potassium elimination, while 10% is excreted in stool 3, 5
• Renal potassium excretion is maintained until GFR decreases to less than 10-15 mL/min/1.73 m² 3, 4
• Factors regulating potassium secretion include:
  • Prior potassium intake
  • Intracellular potassium levels
  • Delivery of sodium chloride to the distal nephron
  • Urine flow rate
  • Hormones such as aldosterone and beta-catecholamines 5

Potassium and Blood Pressure Regulation

• Dietary potassium is inversely related to blood pressure in multiple studies 3
• Potassium interventions have been effective in lowering blood pressure, especially in those consuming excess sodium and in Black individuals 3
• The typical BP-lowering effect of potassium supplementation is about 2 mmHg in normotensive adults and 4-5 mmHg in hypertensive adults 3
• The sodium/potassium ratio may be more important for blood pressure control than either electrolyte alone 3

Consequences of Potassium Imbalance

Hypokalemia (Low Potassium)

• Can result from inadequate intake, increased gastrointestinal or renal losses, or redistribution into cells 6
• Clinical manifestations include:
  • Weakness and fatigue
  • Cardiac arrhythmias with prominent U-waves on ECG
  • In advanced cases, flaccid paralysis and impaired urine concentration 1
  • Postural hypotension, glucose intolerance, and metabolic alkalosis 7

Hyperkalemia (High Potassium)

• Common in patients with chronic kidney disease stage 5 3
• Can cause alterations in muscle function and cardiac arrhythmias 3
• When severe, can rapidly lead to death from cardiac arrest or paralysis of respiratory muscles 3
• Risk factors include renal failure, acidosis, rhabdomyolysis, and certain medications 3

Dietary Recommendations

• The 2015 Dietary Guidelines for Americans identify the adequate intake level for adults as 4700 mg/day 3
• The World Health Organization recommends potassium intake of at least 3510 mg per day from food 3
• Good dietary sources include:
  • Fruits and vegetables
  • Low-fat dairy products
  • Selected fish and meats
  • Nuts and soy products 3
• Four to five servings of fruits and vegetables typically provide 1500 to >3000 mg of potassium 3

Special Considerations

• In patients with CKD stages 2-5 and 5D who have or are at risk of hyperkalemia, potassium intake should be limited 3
• Potassium-rich diets are generally preferred over supplements for potassium repletion in most patients 3
• The balance between sodium and potassium is critical, as imbalances in the potassium/sodium ratio are associated with increased risk for hypertension and cardiovascular disease 3

Common Pitfalls in Management

• Assuming normal serum potassium levels rule out the risk of significant total body potassium depletion 5
• Failing to consider medications that can affect potassium balance (diuretics, ACE inhibitors, ARBs) 3, 4
• Not recognizing that acidosis can cause shifts of potassium from intracellular to extracellular space 8
• Overlooking that salt substitutes often contain potassium and may cause hyperkalemia in susceptible individuals 3