Who says you need to drink eight glasses of water a day?

Answers to your questions about the news.
April 4 2008 4:23 PM

Who Says You Need Eight Glasses a Day?

The history of a debunked theory.

A glass of water
A glass of water

A recent editorial (PDF) in the Journal of the American Society for Nephrology is getting wide press coverage for debunking the so-called "8x8" theory—the popularly held belief that drinking eight 8-ounce glasses of water daily helps remove toxins, improve skin tone, and increase satiety, among other health benefits. The authors chalk up the belief to folklore, and newspaper reports claim ignorance as to its provenance. Just how long has this idea been around?

Two-hundred years, at least. The most commonly cited source for the 8x8 myth—highlighted in this 2002 review paper by a Dartmouth professor—is the U.S. government-sponsored Food and Nutrition Board. * The board's "Recommended Dietary Allowances" from 1945 include the following advice:

A suitable allowance of water for adults is 2.5 liters daily in most instances. An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods.

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According to this theory, people ignored the last part of the statement, which points out that you can get most of that water just by eating. If you actually had to drink all 2.5 liters, you'd need around 10 8-ounce glasses per day. By 1959, the concept was so entrenched that Groucho Marx could joke about self-righteous centenarians who claim that they eat "raw turkey liver" for breakfast and drink "thirty-two glasses of water a day" instead of "eight glasses a day like the rest of us."

However, the Explainer has uncovered evidence of the 8x8 myth going all the way back to 1796, in a German text by Dr. Christoph Wilhelm Hufeland called Makrobiotik. The book includes an anecdote about the surgeon general to the king of Prussia, a vibrant 80-year-old man who had "contracted the habit of drinking daily from seven to eight glasses" of cold water and thus "enjoyed much better health than in his youth." (An English translation is available in this book from 1843.)

The hydrotherapy craze that swept through Europe and then America in the late 19th century encouraged the notion that people needed to be drinking more water. By 1900, the New York Evangelist reported that a women's association on the Lower East Side was being instructed by a Dr. Vinton that one needed to ingest "at least eight glasses of water a day" and take "four times as much water as food." (Incidentally, the girls were also told that it was dangerous to get one's feet wet, that it wasn't good to "wear many skirts," and that their brains were "soft like jelly.") By the 1910s and 1920s, the popular press was full of exhortations to consume six to eight glasses on a daily basis. Charles Atlas, the bodybuilder whose famous comic-strip ads were highly popular from the '20s through the '70s, was fond of recommending the same amount.

In more recent decades, there have been plenty of proponents of the 8x8 theory. In 1967, Dr. Irwin Stillman, one of the earliest advocates of a high-protein, low-carbohydrate diet, insisted that his followers drink eight glasses of water a day in order to wash away ketones, or "ashes left in the furnace." The controversial 1992 bestseller Your Body's Many Cries for Water, which calls for a minimum of eight to 10 glasses of pure water a day (not coffee, not soda), probably played a role in spreading the myth, as has the bottled-water industry, which has exploded since the 1980s.

Got a question about today's news? Ask the Explainer.

Explainer thanks Katharine Donahue of UCLA; Elizabeth Royte, author of Bottlemania; and James Wharton of the University of Washington.

Correction, April 7, 2008: The original story incorrectly referred to the Food and Nutrition Board as a U.S. government agency. The Food and Nutrition Board is a private nonprofit organization. (Return  to the corrected sentence.)

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