What is the best way of restoring the body’s fluid balance - by constantly sipping from a bottle of water or taking an occasional big drink?
Seventy per cent of an adult’s body is water. Two and a half litres are lost every day in urine and water that evaporates from the skin. This loss must be offset by a daily intake of the same amount: 1.5 litres by drinking fluids and the rest via solid food.
"We have a sensation of thirst when the body’s water loss reaches 0.5 per cent," said Susann-Catherine Ruprecht, spokeswoman for the German Institute of Human Nutrition. Drinking a glass of water is the simplest solution.
Antje Gahl, spokeswoman for the German Nutrition Society, recommends ingesting fluids evenly throughout the day. It is not possible to build fluid reserves because the body can only process small amounts, excreting the rest.
This is where the problem lies. When people ignore thirst and take too long before drinking, the depleted water stores make themselves felt. "At a fluid loss of about three per cent, physical and mental aptitude becomes impaired," Ruprecht said. Symptoms may include a headache, fatigue and difficulty concentrating.
Normally this is not serious. At temperate latitudes, a danger of dehydration arises only in extreme situations. People with enough to eat and drink supply their bodies with sufficient fluids, argues Uwe Knop, author of a book on hunger and appetite.
"Drinking is such an essential mechanism that you don’t need any rules for it," Knop said, referring to guidelines on the amount of water that should be drunk daily. "A healthy person doesn’t need anything like a ’drink alarm’. You can simply drink when you feel like it."
Whether one drinks in accordance with guidelines or heeds the sensation of thirst, it is important to bear in mind that the necessary amount of fluids varies. The body requires more during strenuous activity such as exercise, when many people tend to ignore thirst.
"Not drinking enough during athletic activities is a known problem," noted Daniel Koenig, director of the Institute for Sport and Sport Science at Freiburg University in Germany. He does not favour rigid recommendations on fluid intake, however. And said that jogging for 20 minutes was not strenuous; after an hour of physical exertion, however, one should pay attention to fluid intake.
Experts agree that there is no danger of drinking too much - neither during everyday activities nor during heavy exercise. "The body can handle 10 litres a day with no problem," Gahl said.
Koenig said the only known cases of overhydration-related fatalities occurred during extreme sporting events such as double marathons. "Overdrinking causes the body to lose too much sodium, among other things," he said. According to the DGE, only excessive drinking of sweet beverages is harmful in the long term.
So if you are not running a marathon, you’re on the safe side by drinking when you’re thirsty. But you should not wait too long. "You can’t quickly offset heavy fluid loss," Ruprecht said. Restoring the body’s fluid balance can take up to 24 hours.