A new hydration index has produced some interesting results. It turns out that beer and coffee are not as bad as they are made out to be. And milk hydrates the body even better than water.
How much water a person should drink each day to stay healthy and perform well is a question that concerns many people. Experts give many different answers. Some say 1 litre, others advise 2 or even 3 litres a day, and more in summer. There is also another approach.
A new “beverage hydration index” now provides the first empirical data. On this basis, recommendations have been developed on which drinks hydrate the body most effectively. The index was developed by specialists at Loughborough University in the UK and answered the question of how long 13 well-known drinks remain in the body after you drink them. It is the first study to look at hydration in people who are not exercising. The results were published in the American Journal of Clinical Nutrition.
The study participants were 72 men aged 20 to 30. Each drank a litre of water plus one to three other popular drinks within 30 minutes.
The amount of water not excreted after 4 hours was given a value of 1.0. The volume of each of the other drinks remaining in the body was expressed in proportion to this. A value above 1.0 indicates that more fluid stays in the body; a lower value indicates a faster rate of excretion than water.
The result was striking: 3 drinks had a significantly higher hydration index than water. These were whole milk, skimmed milk and special oral rehydration solutions such as Pedialyte. All of them reached values of 1.5. Orange juice also scored 1.1 — better than water. All the other drinks, such as iced tea, cola, hot tea, coffee, beer and sparkling water, performed equally, slightly below water.
Maughan RJ, Watson P, Cordery PA, Walsh NP, Oliver SJ, Dolci A, Rodriguez-Sanchez N, Galloway SD: “A randomized trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index” — published in the American Journal of Clinical Nutrition, March 2016.
The study’s lead author, Ronald J. Maughan, explained in a New York Times blog: “Normally the kidneys respond to water in the usual way and, to get rid of the excess water, they produce more urine. However, if a drink — as in the case of milk — contains minerals such as sodium and potassium, which act as electrolytes, the stomach empties more slowly. The kidneys work more gently, and the fluid stays in the body longer.”
Contrary to popular belief, caffeine, alcohol and sugary drinks can be enjoyed in moderation. The dehydrating effect of coffee and beer is an unproven myth. Even soft drinks hydrate the body just as well as water, although they contain sugar and nutrition experts advise against them.
The study’s results suggest the following recommendations. On a long journey without access to fluids, milk is a good choice. The same is true for older people, whose sense of thirst is reduced, and for young children who are dehydrated, especially in summer. It is important to remember, however, that milk contains far more calories than water.
