Hydration is critical for athletic performance, with general guidelines recommending at least 3–4 liters of water per day for active individuals, adjusted so that urine remains pale yellow. During exercise, athletes should aim for 400–800 mL per hour depending on sweat rate and environmental conditions. Even a 2% loss of body weight from fluid can impair performance by 10–20%. Signs of dehydration include dark yellow urine, thirst, dry mouth, headache, dizziness, fatigue, decreased performance, elevated heart rate, and reduced sweat rate.
Electrolytes — minerals that carry an electrical charge, including sodium, potassium, chloride, calcium, and magnesium — regulate fluid balance, nerve function, and muscle contraction. Athletes lose substantial electrolytes through sweat, particularly sodium at 500–1500 mg per liter of sweat. Sodium is the primary electrolyte lost in sweat and is essential for regulating fluid balance, nerve impulses, and muscle contractions. Hyponatremia — dangerously low blood sodium levels below 135 mmol/L — is often caused by drinking excessive water without adequate sodium replacement during prolonged exercise, and can cause nausea, confusion, seizures, and even death. Sports drinks containing water, 6–8% carbohydrates, and electrolytes are beneficial during exercise lasting longer than 60 minutes or in hot conditions; for shorter sessions, water is usually sufficient. Drinks can be classified as isotonic (matching blood osmolality, ideal for balanced replacement), hypotonic (faster fluid absorption with less energy), or hypertonic (more energy but slower absorption). Potassium works alongside sodium to regulate fluid balance and muscle contractions, with athletes needing 3500–4700 mg per day from foods like bananas, potatoes, and spinach.
Micronutrients — vitamins and minerals required in small amounts — do not provide energy but are critical for metabolism, immune function, bone health, and hundreds of enzymatic reactions. Iron is essential for hemoglobin and myoglobin, and deficiency impairs endurance performance and causes fatigue; the RDA is 8 mg for males and 18 mg for females, with female and endurance athletes at higher risk. Sports anemia (pseudoanemia) is a dilutional decrease in hemoglobin caused by expanded plasma volume in endurance athletes and is a normal adaptation rather than true anemia. Calcium supports bone health, muscle contraction, nerve signaling, and blood clotting, with athletes needing 1000–1300 mg per day. Vitamin D supports calcium absorption, bone health, immune function, and muscle function, with many athletes deficient, especially those training indoors; supplementation of 1000–2000 IU per day is often recommended. B vitamins serve as coenzymes in energy metabolism, magnesium is involved in over 300 enzymatic reactions including energy production and muscle contraction (with athletes potentially needing 400–600 mg per day), and zinc supports immune function, protein synthesis, and testosterone production. Antioxidants from whole foods neutralize free radicals produced during exercise, though excessive supplementation may blunt training adaptations because some oxidative stress is needed to signal adaptation.