from journal Medicine and Science in Sports & Exercise
People who exercise outdoors in hot weather are cautioned to drink adequate liquids to keep hydrated. Scientific studies show dehydration affects ability to regulate body temperature, muscle endurance and even kidney function. Dehydration may also affect your mind. Georgia Tech researchers compared data from more than thirty studies. They confirmed that cognitive functions—attention, coordination and complex problem solving—were affected as the body lost water--not just people involved in vigorous outdoor activity in hot weather, since older people and people with high body fat can become dehydrated more easily. Authors also caution in the journal Medicine and Science in Sports & Exercise that hydration is important, but too much water can be harmful.