Electrolyte

What Is an Electrolyte?

An electrolyte is any substance that dissociates into ions when dissolved in water, producing a solution that conducts electricity. In nutrition and physiology, the term refers specifically to the mineral ions dissolved in body fluids that are essential for maintaining electrical gradients, fluid balance, and pH across compartments. The major electrolytes in the body are sodium (Na+), potassium (K+), chloride (Cl-), bicarbonate (HCO3-), calcium (Ca2+), magnesium (Mg2+), and phosphate (HPO4 2-).

Key Physiological Roles

• Fluid distribution: Electrolytes create osmotic pressure that determines how water is distributed between intracellular fluid, extracellular fluid, and the vascular space. Sodium is the dominant extracellular cation; potassium is dominant intracellularly.
• Action potentials: Nerve impulses and muscle contractions depend on rapid ion movements across cell membranes. Sodium flows in (depolarization); potassium flows out (repolarization). Calcium triggers muscle contraction.
• Acid-base balance: Bicarbonate, phosphate, and protein buffer systems maintain blood pH within the narrow physiological range of 7.35-7.45.
• Cardiac function: The precise balance of sodium, potassium, calcium, and magnesium is required for rhythmic heart contraction.

Electrolyte Loss and Replacement

Electrolytes are lost primarily through sweat, urine, and gastrointestinal secretions. During prolonged physical activity, sweat losses can exceed 1 liter per hour and contain approximately 900 mg sodium, 200 mg potassium, 15 mg calcium, and 13 mg magnesium per liter. Drinking plain water during prolonged endurance exercise without replacing sodium can dilute blood sodium, causing exercise-associated hyponatremia — a potentially fatal condition characterized by nausea, headache, confusion, and seizures.

Sports drinks typically contain 400-700 mg sodium and 100-200 mg potassium per liter. For most moderate exercise lasting less than 60-90 minutes, water alone is sufficient. Whole foods such as bananas, oranges, salted pretzels, and dairy products are effective post-exercise electrolyte sources for recreational athletes.

Clinical Imbalances

Electrolyte imbalances — whether from disease, medication, excessive sweating, vomiting, diarrhea, or kidney dysfunction — can be life-threatening. Hyponatremia, hyperkalemia, hypocalcemia, and severe hypomagnesemia all require prompt medical evaluation. Routine electrolyte panels in blood tests measure sodium, potassium, chloride, and bicarbonate to screen for imbalances.