Electrolytes 101: What They Are and What They Do

Electrolytes are minerals that carry an electrical charge when dissolved in water. The major players are:

• Sodium (Na+): Main regulator of fluid in the bloodstream and spaces outside cells; critical for nerve signals and absorption of water and glucose in the gut.
• Potassium (K+): Primary electrolyte inside cells; essential for heart rhythm and muscle contraction.
• Chloride (Cl−): Partners with sodium to maintain fluid balance and stomach acid production.
• Magnesium (Mg2+): Supports muscle relaxation, energy metabolism, and nerve function.
• Calcium (Ca2+): Key for muscle contraction and signaling.
• Phosphate and bicarbonate: Help buffer pH and support cellular energy systems.

Hydration is the balance of water across cell membranes. Your body manages this via osmolality (the concentration of dissolved particles), hormones (ADH/vasopressin and aldosterone), and the kidneys. Electrolytes are the levers the body pulls to move water where it’s needed.

Why Water Alone Isn’t Always Enough

• Sweat removes water and electrolytes, especially sodium. Losses vary widely: sodium can range from about 200–1,000+ mg per liter of sweat. Sweat rate can vary from ~0.3–2.0+ L per hour.
• Drinking only plain water during heavy sweating can dilute blood sodium, increasing the risk of hyponatremia (dangerously low sodium).
• Glucose and sodium co-transport in the intestine (SGLT1) speeds water absorption—this is why solutions with modest sugar and sodium rehydrate faster than water alone.

Symptoms of imbalance can include fatigue, headache, foggy thinking, dizziness, nausea, muscle cramps, or an unusually high heart rate for your effort level.

When Is Water Enough vs. When to Add Electrolytes

• Water is typically enough when:

  • Activity lasts under 60 minutes in a cool environment.
  • Sweat loss is light and you’re eating balanced meals with salt.

• Add electrolytes when:

  • Exercise or work exceeds 60–90 minutes, especially in heat or humidity.
  • You’re a “salty sweater” (visible salt on hat/shirt, burning eyes, salty taste).
  • At altitude, in hot or very cold environments, or during endurance events.
  • You’re on low-carb/keto diets (they increase sodium loss), or taking diuretics.
  • You have vomiting/diarrhea or fever (use oral rehydration solutions).

What Makes an Effective Hydration Drink

The best hydration drinks balance fluid with electrolytes and a modest amount of carbohydrate to enhance absorption and energy.

• Electrolytes:

  • Sodium: about 300–700 mg per liter (13–30 mmol/L) for most; up to 1,000 mg/L for very salty sweaters or extreme heat.
  • Potassium: about 200–250 mg per liter (~5–6 mmol/L).
  • Chloride roughly matches sodium; small amounts of magnesium and calcium can help but aren’t usually critical acutely.

• Carbohydrate:

  • 3–6% solution (30–60 g per liter) for most training; supports faster absorption and energy without slowing gastric emptying.
  • Higher sugar (>8–10%) can slow stomach emptying and may cause GI upset during exercise.

• Osmolality: Aim for roughly 200–300 mOsm/kg (isotonic to slightly hypotonic).

Tip: You can “salt to taste.” If a drink tastes pleasantly salty during/after sweat-heavy activity, you likely need it; if it tastes too salty, dilute.

Oral Rehydration Solutions (Illness and Severe Dehydration)

Medically validated formulas used worldwide for dehydration from diarrhea and vomiting rely on sodium-glucose co-transport for rapid rehydration.

• WHO standard (per liter): ~75 mmol sodium, ~75 mmol glucose, chloride ~65 mmol, potassium ~20 mmol, citrate ~10 mmol; osmolarity ~245 mOsm/L.
• Simple home recipe: Mix 1 liter clean water + 6 level teaspoons sugar + 1/2 level teaspoon salt. Add flavor and a source of potassium (e.g., a splash of orange juice) if desired.
• Seek medical care for infants, frail adults, signs of shock, blood in stool, or persistent vomiting.

Food First: Everyday Sources of Electrolytes

• Sodium: Table salt, broths, pickles, olives, salted nuts, cheese.
• Potassium: Potatoes, bananas, beans, yogurt, tomatoes, leafy greens, coconut water (note: low sodium).
• Magnesium: Nuts, seeds, legumes, whole grains, dark chocolate.
• Calcium: Dairy, fortified plant milks, tofu set with calcium, leafy greens.

Eating balanced meals with salt to taste covers most day-to-day needs. Electrolyte drinks are tools for specific situations, not replacements for a good diet.

How Much to Drink: Practical Targets

• Day-to-day:

  • Let thirst guide, aiming for pale-straw urine most of the day.
  • Most adults land around 2–3 liters of fluid daily from beverages and food, but needs vary widely.

• During exercise:

  • General starting point: 0.4–0.8 L per hour, adjusted to conditions and your sweat rate.
  • Electrolytes: About 300–800 mg sodium per hour for heavy sweaters/heat; adjust to taste and signs.
  • Carbs: 30–60 g per hour for sessions over ~90 minutes; up to 90 g/h in long endurance if tolerated.

• After exercise:

  • Replace about 125–150% of the fluid you lost over the next 2–4 hours, including electrolytes.
  • Estimate sweat loss: Body mass change (kg) ≈ liters lost. Example: 1.0 kg lost ≈ ~1.0 L sweat.

Dialing It In: Measure Your Sweat Rate

1. Weigh yourself nude or in dry minimal clothing before and after a workout.
2. Track fluids you drank and urine you produced during the session.
3. Sweat rate (L/hour) ≈ [pre-weight − post-weight (kg)] + fluids consumed (L) − urine (L), all divided by hours.

Use this to personalize how much you drink per hour in similar conditions.

Muscle Cramps: Not Just Electrolytes

Cramps have multiple causes: neuromuscular fatigue, pacing, heat, and sometimes electrolyte deficits. For some “salty sweaters,” sodium intake helps. Strategies include adequate training, pacing, conditioning in heat, and trialing sodium and carbohydrate plans in training.

Special Considerations

• Older adults: Thirst may be blunted; schedule fluids and include some sodium if appetite is low.
• Pregnancy and breastfeeding: Higher fluid needs; include potassium-rich foods and salt to taste.
• High-altitude or cold exposure: Increase fluid and electrolyte awareness; respiration and dry air increase water loss.
• Low-carb/keto: Increased sodium and water loss; consider 1,500–2,300 mg additional sodium spread through the day, unless medically contraindicated.
• Medical conditions: If you have kidney disease, heart failure, hypertension, are on diuretics, ACE inhibitors/ARBs, or potassium-sparing meds, discuss electrolyte strategies with your clinician.

Safety: Too Little vs. Too Much

• Hyponatremia: Often from overconsuming plain water during prolonged exercise; symptoms include headache, confusion, swelling of hands/feet, nausea. Prevent by matching intake to sweat and including sodium.
• Hypernatremia: From severe dehydration; prioritize rehydration and electrolytes.
• Potassium: Excess supplements can be dangerous, especially with certain medications or kidney issues. Get most from food.
• Magnesium: Supplemental forms can cause GI upset; the tolerable upper intake for supplemental magnesium is ~350 mg/day for many adults.
• Caffeine and alcohol: Caffeine’s diuretic effect is mild in habituated users; alcohol increases urine output—rehydrate with electrolytes if consuming.

Quick Plans You Can Use

• Desk day:

  • Drink to thirst; include salty and potassium-rich foods with meals.

• Workout under 60 minutes (temperate):

  • Water is usually enough; eat a normal meal with salt afterward.

• Hot/endurance session over 60–90 minutes:

  • Start with 0.4–0.8 L per hour of a drink containing 300–700 mg sodium/L and 3–6% carbohydrate; adjust to taste and sweat rate.

• After GI illness:

  • Use oral rehydration solution until urine is pale and you feel better; seek care for severe or persistent symptoms.

Key Takeaways

• Hydration = water + electrolytes in the right balance for your conditions.
• Sodium is the primary lever for fluid balance during sweat-heavy activities.
• Modest sugar plus sodium speeds absorption; extremely sugary drinks can slow it.
• Personalize by measuring sweat rate, monitoring urine color, and learning your “salty sweater” cues.
• Use electrolyte drinks strategically; rely on food for most daily electrolyte needs.