How to Hydrate: A Special Report that Answers the Question Why Should I Drink Water

By Rachael Moeller Gorman, "Glass Half Full?," July/August 2011

Why drink water? A report on the connection between water and health.

This is an extreme example, though. Had Jill been sitting at her desk while slightly dehydrated, she wouldn’t have collapsed, but she would have felt thirsty, probably tired, a bit irritable and less willing to work. Her brain would have suffered as well—at least until she drank something. Studies have found that slight dehydration worsens our ability to recall new information. Other studies show that our ability to pay attention and do math is also impaired. This mild, 2 percent dehydration, while fairly common, makes it difficult to be physically active. Several studies have reported that being dehydrated, especially when it’s hot, reduces the amount of aerobic exercise you can do: people who were just slightly dehydrated were typically only able to run, for example, about 75 percent as hard as usual.

When you skimp on fluids, it’s hard on your body, which makes sense because water is essential to just about every process in our body and, in fact, to the very existence of life on Earth. Life first emerged in the salty, primordial ocean; it stayed there until it was able to capture a bit of that water inside itself, the so-called “milieu intérieur” in which cells are bathed. Our inner ocean is a calm, salty broth providing cells with the raw materials they need to function, removing waste products, allowing them to communicate with each other and buffering them from the unpredictable world outside.

All told, this water within accounts for about 60 percent of our body—that’s about 11 gallons, or 92 pounds, inside a 155-pound person. Most of it lurks inside our cells (where all sorts of important substances are dissolved in water) and outside them (the milieu intérieur), but, importantly, we also use it to cool our body with sweat, to circulate oxygen and fuel to our organs, and to take away waste products via blood. The elderly, infants and sick kids are most prone to dehydration, but no one is risk-free. “If you’re really busy, it’s easy for all morning to go by and you don’t really drink much until you notice you are thirsty, at which point you’re already slightly dehydrated,” says Cheuvront. And when we exercise hard, such as playing soccer or football or running distances in the summer, and forget to hydrate, we can easily lose 4 to 5 percent of our body weight.

Next: More on the Importance of Hydration »

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