Is water the best hydration drink?

Which is most hydrating: water, milk, soda, coffee, or beer? Amby Burfoot gives us the surprising results in the New York Times.

The British study determined the hydration index of 13 common beverages by having the participants, 72 males in their mid-20s, drink a liter of water as the standard beverage. The amount of water still remaining in subjects’ bodies two hours later — that is, not voided in urine — was assigned a score of 1.0. All other beverages were evaluated in a similar manner, and then scored in comparison to water. A score higher than 1.0 indicated that more of the beverage remained in the body as compared to water, while a score lower than 1.0 indicated a higher excretion rate than water.

The results showed that four beverages — oral rehydration solution, like Pedialyte; fat-free milk; whole milk and orange juice — had a significantly higher hydration index than water. The first three had hydration index scores around 1.5, with orange juice doing slightly better than water at 1.1. Oral rehydration solutions are specifically formulated to combat serious dehydration such as that resulting from chronic diarrhea.

...Why is milk so efficient at rehydration? “Normally when you drink, it signals the kidneys to get rid of the extra water by producing more urine,” Dr. Maughan said. “However, when beverages contain nutrients and electrolytes like sodium and potassium, as milk does, the stomach empties more slowly with a less dramatic effect on the kidneys.”

Perhaps surprisingly, drinks containing moderate amounts of caffeine and alcohol or high levels of sugar had hydration indexes no different from water. In other words, coffee and beer are not dehydrating, despite common beliefs to the contrary. The study also showed that regular soda can hydrate you just as well as water, although soda contains sugar and most sports and nutrition experts do not recommend it for hydration.

The hydration index could prove useful when making decisions about what beverages to consume and when. For example, if you’re going on a long drive and won’t have access to fluids (or to bathrooms), you’d be smarter to drink milk with its high hydration index rather than water or iced coffee. But don’t forget that milk has many more calories than water, so don’t overdo it, either.

Read more here.