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Claim: The average person needs to drink eight glasses of water per
day to avoid being "chronically dehydrated."
Status: False.
Example: [Collected via e-mail, 2001]
75% of Americans are chronically dehydrated.
In 37% of Americans, the thirst mechanism is so weak that it is often
mistaken for hunger.
Even mild dehydration will slow down one's metabolism as much as 3%.
One glass of water shut down midnight hunger pangs for almost 100% of
the dieters studied in a U-Washington study.
Lack of water is the number one trigger of daytime fatigue.
Preliminary research indicates that 8-10 glasses of water a day could
significantly ease back and joint pain for up to 80% of sufferers.
A mere 2% drop in body water can trigger fuzzy short-term memory,
trouble with basic math, and difficulty focusing on the computer screen
or on a printed page.
Drinking 5 glasses of water daily decreases the risk of colon cancer by
45%, plus it can slash the risk of breast cancer by 79%, and one is 50%
less likely to develop bladder cancer.
Are you drinking a healthy amount of water each day?
Origins: "You need to drink eight to ten glasses of water per day to be
healthy" is one of our more widely-known basic health tips. But do we
really need to drink that much water on a daily basis?
In general, to remain healthy we need to take in enough water to replace
the amount we lose daily through excretion, perspiration, and other
bodily functions, but that amount can vary widely from person to person,
based upon a variety of factors such as age, physical condition,
activity level, and climate. The "8-10 glasses of water per day" is a
rule of thumb, not an absolute minimum, and not of all of our water
intake need come in the form of drinking water.
The origins of the 8-10 glasses per day figure remain elusive. As a Los
Angeles Times article on the subject reported:
Consider that first commandment of good health: Drink at least eight
8-ounce glasses of water a day. This unquestioned rule is itself a
question mark. Most nutritionists have no idea where it comes from. "I
can't even tell you that," says Barbara Rolls, a nutrition researcher at
Pennsylvania State University, "and I've written a book on water."
Some say the number was derived from fluid intake measurements taken
decades ago among hospital patients on IVs; others say it's less a
measure of what people need than a convenient reference point,
especially for those who are prone to dehydration, such as many elderly
people.
The consensus seems to be that the average person loses ten cups (where
one cup = eight ounces) of fluid per day but also takes in four cups of
water from food, leaving a need to drink only six glasses to make up the
difference, a bit short of the recommended eight to ten glasses per day.
But according to the above-cited article, medical experts don't agree
that even that much water is necessary:
Kidney specialists do agree on one thing, however: that the 8-by-8
rule is a gross overestimate of any required minimum. To replace daily
losses of water, an average-sized adult with healthy kidneys sitting in
a temperate climate needs no more than one liter of fluid, according to
Jurgen Schnermann, a kidney physiologist at the National Institutes of
Health.
One liter is the equivalent of about four 8-ounce glasses. According to
most estimates, that's roughly the amount of water most Americans get in
solid food. In short, though doctors don't recommend it, many of us
could cover our bare-minimum daily water needs without drinking anything
during the day.
Certainly there are beneficial health effects attendant with being
adequately hydrated, and some studies have seemingly demonstrated
correlations between such variables as increased water intake and a
decreased risk of colon cancer. But are 75% of Americans really
"chronically dehydrated," as claimed in the anonymous e-mail quoted in
our example? Many of the notions (and dubious "facts") presented in that
e-mail seem to have been taken from the book Your Body's Many Cries for
Water, by Fereydoon Batmanghelidj. Dr. Batmanghelidj, an Iranian-born
physician who now lives in the U.S., maintains that people "need to
learn they're not sick, only thirsty,'' and that simply drinking more
water "cures many diseases like arthritis, angina, migraines,
hypertension and asthma." However, he arrived at his conclusions through
reading, not research, and he claims that his ideas represent a
"paradigm shift" that required him to self-publish his book lest his
findings "be suppressed.''
Other doctors certainly take issue with his figures:
[S]ome nutritionists insist that half the country is walking around
dehydrated. We drink too much coffee, tea and sodas containing caffeine,
which prompts the body to lose water, they say; and when we are
dehydrated, we don't know enough to drink.
Can it be so? Should healthy adults really be stalking the water cooler
to protect themselves from creeping dehydration?
Not at all, doctors say. "The notion that there is widespread
dehydration has no basis in medical fact," says Dr. Robert Alpern, dean
of the medical school at the University of Texas Southwestern Medical
Center in Dallas.
Doctors from a wide range of specialties agree: By all evidence, we are
a well-hydrated nation. Furthermore, they say, the current infatuation
with water as an all-purpose health potion — tonic for the skin, key to
weight loss — is a blend of fashion and fiction and very little science.
Additionally, the idea that one must specifically drink water because
the diuretic effects of caffeinated drinks such as coffee, tea, and soda
actually produce a net loss of fluid appears to be erroneous. The
average person retains about half to two-thirds the amount of fluid
taken in by consuming these types of beverages, and those who regularly
consume caffeinated drinks retain even more.
Regular coffee and tea drinkers become accustomed to caffeine and
lose little, if any, fluid. In a study published in the October issue of
the Journal of the American College of Nutrition, researchers at the
Center for Human Nutrition in Omaha measured how different combinations
of water, coffee and caffeinated sodas affected the hydration status of
18 healthy adults who drink caffeinated beverages routinely.
"We found no significant differences at all," says nutritionist Ann
Grandjean, the study's lead author. "The purpose of the study was to
find out if caffeine is dehydrating in healthy people who are drinking
normal amounts of it. It is not."
The same goes for tea, juice, milk and caffeinated sodas: One glass
provides about the same amount of hydrating fluid as a glass of water.
The only common drinks that produce a net loss of fluids are those
containing alcohol — and usually it takes more than one of those to
cause noticeable dehydration, doctors say.
The best general advice (keeping in mind that there are always
exceptions) is to rely upon your normal senses. If you feel thirsty,
drink; if you don't feel thirsty, don't drink unless you want to. The
exhortation that we all need to satisfy an arbitrarily rigid rule about
how much water we must drink every day was aptly skewered in a letter by
a Los Angeles Times reader:
Although not trained in medicine or nutrition, I intuitively
knew that the advice to drink eight glasses of water per day was
nonsense. The advice fully meets three important criteria for being
an American health urban legend: excess, public virtue, and the
search for a cheap "magic bullet."
Last updated: 31 December 2005
The URL for this page is
http://www.snopes.com/medical/myths/8glasses.asp
Urban Legends Reference Pages © 1995-2006
by Barbara and David P. Mikkelson
This material may not be reproduced without permission.
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Sources:
Batmanghelidj, Fereydoon. Your Body's Many Cries for Water.
Global Health Solutions, 1995. ISBN 0-962-99423-5.
Carey, Benedict. "Hard to Swallow."
Los Angeles Times. 20 November 2001 (Health; p. 1).
Foreman, Judy. "The Water Fad Has People Soaking It Up."
The Boston Globe. 11 May 1998 (p. C1).
Hoolihan, Charlie. "Body Needs Plenty of Water to Work."
The [New Orleans] Times-Picayune. 31 May 1998.
CNN.com. "Americans Need to Shake Salt Habit."
11 February 2004.
Los Angeles Times. "All That Water Advice Just Doesn't Wash."
15 January 2001 (Health; p. 7).
Los Angeles Times. "Readers Take Issue with Article About Water
Consumption."
25 January 2000 (Health; p. 5).
The Toronto Star. "Distilling Water Facts from Water Fiction."
21 March 1999.
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