Overview
- Health authorities are urging people to drink more during the heat but to avoid drinking very large volumes quickly because the kidneys have a practical limit of about 0.8–1.0 liters per hour.
- A peer‑reviewed trial published in the American Journal of Clinical Nutrition found that whole milk, skimmed milk and a commercial oral rehydration solution produced less urine than still water over four hours in 72 healthy men, indicating greater short‑term fluid retention.
- The trial’s findings are limited by its narrow sample (young, healthy men) and short observation window, so milk and ORS are contextual alternatives rather than replacements for water for most people.
- Early signs of water intoxication—dizziness, pounding headache, nausea or vomiting—can mimic heat illness, and continued overdrinking can raise brain pressure and lead to seizures, breathing problems or loss of consciousness; vulnerable people include endurance athletes, very young children, older adults and those with medical conditions affecting fluid balance.
- Practical advice for hot days is to sip small amounts regularly, replace lost salts with electrolyte drinks or salty snacks after heavy sweating, use water as the everyday first choice, and remember milk brings calories and lactose/allergy concerns while sugary soft drinks and pure fruit juices are poor rehydration options.