Drink to thirst — don't overhydrate

What to Do

Drink when you're thirsty, not on a rigid schedule. For runs under 60 minutes, pre-run hydration (8-16 oz in the 1-2 hours before) is usually sufficient. For longer runs, carry water and sip as needed.

Why It Works

A landmark New England Journal of Medicine study of Boston Marathon runners found the strongest predictor of dangerous hyponatremia (low blood sodium) was excessive fluid intake. There are at least a dozen recorded deaths from overhydration in endurance events, but zero confirmed deaths from dehydration as a direct cause in marathon runners. Thirst is a reliable guide for most runners.

Tips

• Electrolytes become important for runs over 60-90 minutes, especially in heat
• For hot weather runs, drink 1 cup every 15-20 minutes during moderate activity
• Check urine color: pale yellow is ideal; clear may indicate overhydration
• Sports drinks are unnecessary for runs under 60 minutes — water is sufficient