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Dehydration Science

Do We Really Need to Drink 8 Glasses of Water Per Day?

Here’s a health tip that we all have heard: “Adults should drink eight 8-ounce glasses of water per day for proper hydration.” But what does the research say? Do we need to follow the 8x8 rule religiously or risk dehydration?

The short answer is: Eight 8-ounce glasses of water per day is generally an adequate guideline for some adults, but in most cases that volume is not necessary.

What the Research Says about the 8x8 Rule

In 2002, a review of research – titled “Drink at least eight glasses of water a day. Really? Is there scientific evidence for “8 × 8”? – was published in the American Journal of Physiology. The article’s author Dr. Heinz Valtin poured over 100 studies, peer-reviewed surveys and research articles to determine the origins of the 8X8 rule and to establish if there was any scientific proof behind it.

Valtin’s conclusion: Healthy adults living in temperate climates, who are mildly active, don’t need to drink such a significant amount of water. Valtin also noted that in addition to the water that we drink, we also receive H2O from beverages other than water and foods, which should also count toward our daily hydration goal.

Of course, for more active people, who exercise regularly, the body’s fluid needs are certainly greater, especially in warm climates, and hydration is advised for the “treatment of some diseases,” Valtin wrote. But ultimately, the literature suggests the 8X8 rule is mostly a myth, he concluded.

How Much Do We Need to Drink Each Day

For healthy adults, the amount of water needed each day depends on a variety of factors, like activeness, body type and climate. And although the 8x8 rule serves as a safe guideline for hydration, our bodies also have a built in drinking clock – the thirst sensation.

According to a 2004 report from the Institute of Medicine, the majority of healthy adults drink enough water each day “by letting thirst be their guide.” In addition, the report provided some hydration standards for both men and women. Men, on average, should consume 125 ounces or 3.8 liters of total water each day, the authors wrote, while women should consume 91 ounces or 2.7 liters.

That makes it sound like the majority of us don’t drink enough each day, but that measure is total water. Therefore, beverages like coffee, tea, milk, juice, soda, and even beer, as well as some foods are included. In other words, our diets can be a significant contributor to our daily fluid requirements.

So ultimately, the 8x8 rule is a good goal for some adults to shoot for, but it isn’t always necessary. Most adults will drink enough by letting thirst guide them.

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