Micronutrients, Hydration, and Electrolytes
Micronutrients, Hydration, and Electrolytes
This domain examines vitamins and minerals that affect performance, plus fluid and sodium balance. Questions often test iron, calcium, vitamin D, B vitamins, sweat rate calculation, sodium losses, and hyponatremia risk.
Core rules
- Iron: heme iron from animal foods is better absorbed; plant iron absorption improves with vitamin C and is inhibited by phytates and polyphenols. Do not supplement without lab evidence of deficiency.
- Calcium and vitamin D: adequate intake supports bone; vitamin D status should be assessed before high-dose supplementation.
- B vitamins are coenzymes in energy metabolism; deficiency impairs performance, but excess does not enhance it.
- Pre-exercise fluid: about 5–10 mL/kg body mass 2–4 hours before exercise.
- During exercise: 400–800 mL/hour is a common starting range; adjust to sweat rate and conditions.
- Sodium: heavy salty sweaters may need 300–600 mg sodium/hour or more; sodium-containing drinks help replace losses and reduce hyponatremia risk.
Worked example
An 80 kg athlete has a sweat rate of 1.2 L/hour and sweats about 800 mg sodium/L. For a 2-hour match: fluid loss ≈ 2.4 L; sodium loss ≈ 1,900 mg. Prehydrate with 400–800 mL in the 2–4 hours before. During the match, drink to limit loss to under 2% body mass, using a 6–8% carbohydrate-electrolyte drink if fuel is also needed. Reasoning: replace a substantial portion of losses without overdrinking; sodium matters when sweat is salty and exercise is prolonged.
Traps
Overhydrating with plain water and causing hyponatremia; taking salt tablets without fluid; assuming all athletes need iron; and using caffeine or glycerol as a substitute for adequate baseline hydration.