Water makes up more than 60 percent of your body weight, and staying hydrated supports important functions such as maintaining body temperature, removing waste and lubricating your joints. When you become dehydrated, whether from illness or playing sports for long periods, you need to drink enough water to replenish your body's stores. But you want to avoid drinking too much water, which can have health consequences, too
Your body loses fluids through sweat, urine and other bodily excretions, such as vomit and diarrhea. It's easy to become dehydrated when you sweat a lot during physical activity, especially if you exercise for a long time in hot weather. If you've been sick and have been vomiting or experiencing diarrhea, you may also become dehydrated. Symptoms of dehydration include thirst; a dry, sticky mouth; decreased urine and urine that is dark in color; headache; and muscle cramps. Severe dehydration may cause confusion, irritability, rapid heartbeat and even loss of consciousness.
Too Much of a Good Thing
When rehydrating yourself, you want to be careful not to drink too much water. This can dilute the concentration of sodium in the blood, a condition called hyponatremia. When this happens, the balance of sodium in the fluids outside your body's cells is disrupted, fluid moves into the cells in an attempt to fix the imbalance and your cells swell. Brains cells are particularly prone to swelling. Symptoms of hyponatremia include confusion, convulsions, fatigue, loss of appetite, irritability and even death.
The Real Reason
It's rare for hyponatremia to result from drinking too much water alone, Joseph Verbalis, chairman of medicine at Georgetown University Medical Center, told "Scientific American." Rather, it results from excess fluid intake combined with increased secretion of a hormone called vasopressin. Secretion of this hormone rises during times of physical stress, such as endurance competitions, and causes the body to hold onto water. If you're also drinking lots of fluids, this may cause the dangerous effects associated with hyponatremia.
Water to the Rescue
Mild to moderate dehydration can be treated by simply drinking water -- but not too much. According to MedlinePlus, if you catch the signs of dehydration early and treat it, you can recover with no problems. After a long bout of exercise, if you feel very thirsty or notice any other mild to moderate symptoms, begin sipping water to rehydrate. Verbalis recommends replacing exactly the amount of fluid you lost and no more. Because most people will find it difficult to measure this amount, he suggests simply drinking to thirst. You'll know your water levels are back to normal when your urine is pale in color.