Electrolytes — Sodium, Potassium, and Fluid Balance

Electrolytes are minerals that carry an electrical charge in body fluids — chiefly sodium, potassium, chloride, calcium, and magnesium. They govern fluid distribution between compartments, nerve impulse transmission, and muscle contraction. During exercise, electrolytes (predominantly sodium) are lost in sweat; large or repeated losses can impair performance and, combined with overdrinking plain water, raise the risk of hyponatremia (see Exercise-Associated Hyponatremia).

Sodium is the principal extracellular electrolyte. The Dietary Guidelines for Americans (2025–2030) set the everyday limit at less than 2,300 mg/day for ages 14 and up (lower limits for younger children) and tell people to avoid highly processed foods high in sodium; the same document notes that highly active individuals may benefit from increased sodium intake to offset sweat losses. The same 2,300 mg figure is the National Academies' 2019 Chronic Disease Risk Reduction Intake for sodium (reduce intake if above it, ages 14+); their Adequate Intake for adults is 1,500 mg/day. This everyday ceiling is distinct from acute replacement during prolonged exercise. The 1996 ACSM fluid-replacement stand recommended 0.5–0.7 g of sodium per liter of drink for exercise over an hour; its 2007 replacement cites sports-drink guidance of roughly 20–30 mEq/L sodium (≈0.46–0.69 g/L), 2–5 mEq/L potassium and 5–10% carbohydrate, adjusted to the event and the weather, to replace sweat electrolytes and help drive thirst and fluid retention. The 2016 AND/DC/ACSM joint position adds that sodium should be taken during exercise when sweat sodium losses are large: sweat rates above 1.2 L/h, salty sweat, or exercise longer than 2 hours. Sweat sodium averages roughly 35–50 mmol/L but varies widely between people.

Potassium is the principal intracellular electrolyte and counterbalances sodium's effect on blood pressure. The 2019 Dietary Reference Intakes set its Adequate Intake at 3,400 mg/day for men and 2,600 mg/day for women (no upper limit and no chronic-disease intake could be set); potassium-rich diets (fruits, vegetables, legumes, dairy) are encouraged, and the DASH pattern (see The DASH Diet) leverages high potassium, calcium, and magnesium to lower blood pressure. For everyday activity, food and water cover electrolyte needs; dedicated electrolyte products earn their place mainly in prolonged, hot, or heavy-sweat exercise (see Hydration Strategy During Exercise).

• Charged minerals: sodium, potassium, chloride, calcium, magnesium.
• Regulate fluid balance, nerve transmission, muscle contraction.
• Sweat loss is mostly sodium; dietary sodium limit <2,300 mg/day (DGA 2025–2030), with more for highly active people losing sweat.
• Sodium DRIs (2019): AI 1,500 mg/day; reduce if above 2,300 mg/day (CDRR). Potassium AI 3,400 mg/day men, 2,600 mg/day women.
• In long sessions: ACSM 2007 cites ~20–30 mEq/L sodium (≈0.46–0.69 g/L) in sports drinks (the 1996 stand said 0.5–0.7 g/L); take sodium when sweat losses are large (>1.2 L/h, salty sweat, >2 h; 2016 joint position).
• Potassium counters sodium's BP effect; DASH emphasizes K, Ca, Mg.