to Swallow: Do You Really Need Eight Glasses of Water Every Day?
years we've been admonished to chug eight glasses of water a day--for our skin,
for our weight, for general good health. But--surprise!--experts say that advice
might not hold water.
about a drinking problem.
the one hand, it seems that more people than ever are drinking heavily: College
students bring bottles into classrooms; office workers nip from jugs all day long.
Many of us are like Gerri Johnson, a 56-year-old kindergarten teacher living in
Manhattan Beach, who says, "I carry a bottle of water throughout the day, and
I'm always drinking. It flushes out my body, and it's good for my skin."
At the same time,
some 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
it be so? Should healthy adults really be stalking the water cooler to protect
themselves from creeping dehydration?
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.
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.
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
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.
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.
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.
I go to the airport I see all these people carrying around bottles of water, and
I wonder, 'What's behind this?' " says Schnermann. "Certainly not science."
The way it's almost always stated, in books, magazines and newspapers, the 8-by-8
rule specifically discounts caffeinated beverages, such as coffee. This is flat
wrong. Caffeine does cause a loss of water, but only a fraction of what you're
adding by drinking the beverage. In people who don't regularly consume caffeine,
for example, researchers say that a cup of java actually adds about two-thirds
the amount of hydrating fluid that's in a cup of water.
is to say, one cup of coffee equals about two-thirds a cup of water--if you're
not a regular caffeine drinker.
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.
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."
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.
Do the Math: We're Drinking Plenty
take a close look at a survey released this May by the International Bottled Water
Assn. Based on interviews with 2,818 adults in 14 U.S. cities, the association
concluded that "although an overwhelming majority of Americans know that drinking
water enhances health, most don't drink as much per day as they should."
to the association's own numbers, Americans say they drink an average of 6.1 glasses
of water, 3.7 servings of soda or sports drinks, 3.2 of coffee and tea, 1.9 of
juice, 1.7 of milk, and one alcoholic drink each day.
told, after subtracting the alcoholic drink, that's a sopping 15 glasses of hydrating
fluids, well above the already exaggerated "minimum." And it doesn't even include
the three or four glasses contained in solid food.
do we do with all this excess water? Ask any water junkie who's tried to sit through
a movie lately: We run to the bathroom.
some people, drinking plenty of water is a very good idea. As we age, for example,
many of us grow less sensitive to losses of body water and don't drink when we
should. Developing a water habit is a good precaution against dehydration. In
addition, researchers have good evidence that people who develop kidney stones
can lower their risk of further problems by drinking more fluids. "Those are the
only patients we would tell to drink more water," says Alpern.
there are also people for whom guzzling water is dangerous. According to Dr. Gary
Robertson, who studies water metabolism at Northwestern University Medical School
in Chicago, these are patients whose bodies have trouble eliminating fluids--for
example, those with diabetes who are taking anti-diuretic hormone, or ADH, which
prevents the body from losing water. "The excess water cannot be excreted," he
says, "and the result is water intoxication, which produces symptoms ranging from
mild headache to confusion, coma, seizures and occasionally even death."
Robertson, doctors are prescribing ADH for conditions such as nocturia, a persistent
need to urinate at night, which ruins sleep in many elderly people; and bed-wetting,
in both older adults and children. He's aware of one case already in which a diabetic
woman taking ADH died of water intoxication after following the advice of an article
discussing the health benefits of water.
course, if you're healthy, and you're laboring over the stair machine, playing
basketball, or even gardening in a hot, dry climate, you're going to need a lot
more than a liter to keep you hydrated. But you hardly need a nutritionist or
a doctor to tell you that.
dying of thirst," says Alpern. "The thirst mechanism is one of the most powerful
and sensitive of all the body's regulatory processes."
Thirst Is Your
says that this mechanism almost always kicks in when we've lost between 1% and
2% of body water. "There's no evidence that this 1 to 2% decrease is harmful in
any way," he says. "Thus, there is really no need to 'prevent' this slight decrease
in body water by drinking a specified amount in the absence of thirst."
What if you're
sweating and for some reason don't or can't drink? That's when the body will begin
to squeeze water from its own tissues, including the brain and the skin. And that's
why you may get a headache when dehydrated, and why your skin can look ragged
and dry. A tall, cool glass of water or soda or iced tea will soothe your head
and revive your skin, in most cases, doctors say--but only if you're dehydrated
to start with.
you're a normally hydrated person, like you or me," says Dr. David Rish, a dermatologist
in Beverly Hills, "then drinking extra water is not going to do anything for your
skin. If your skin is dry, and you're hydrated, the best thing to do is apply
Using Water as a Diet Aid
most cruelly of all, there's no good evidence that drinking water significantly
curbs appetite. "I think that's mostly an invention of the diet industry," says
Carolyn Katzin, a nutritionist in Brentwood who runs the American Cancer Society's
nutrition program in California. "A better way to get water is in fruits and vegetables."
of liters of drinking water certainly fill the stomach, researchers say. But you're
just as hungry shortly thereafter; and once all that water flows under the bridge,
you tend to eat as many calories as you would have without guzzling.
Rolls, the Pennsylvania State researcher, says water can help you eat fewer calories--as
long as it's cooked into food. In a 1999 study, Rolls tallied how many calories
24 healthy adult women ate when served a lunch of chicken and rice. When the chicken
and rice were prepared as a casserole and served with a glass of water, the women
consumed an average of 392 calories each. When the rice, chicken and water were
cooked together into a soup, the women ate an average of only 289 calories each.
"And they did not make up for those calories by eating more at dinner," says Rolls.
really the way the body is engineered to get water--in food, in soup, in fruits
and vegetables, which are almost all water," says UCLA psychologist William McCarthy,
who's also director of science at the Pritikin Longevity Center in Santa Monica.
"When we get water in this food matrix, it stays with us for a while. Whereas
when we drink liquid water, it goes right through the body. I see all these people
carrying around their water bottles like talismans to protect them from disease
and weight gain. Well, lots of that water is going into the stomach--and right
that it's doing any mischief in healthy adults along the way. "You know, I get
patients in my office all the time, saying, 'I've been real good, doc, I'm drinking
seven glasses of water a day,' " says Alpern. "And I leave them alone. It's certainly
not doing them any harm, and it's a lot better than other habits they could have."
doctors say. Forget the diet books. And listen to your own body. Says Ann Grandjean:
"Look, if you're running to the bathroom so much it seems like you can't get any
work done, you're drinking too much. And if you're going less than four times
a day, you're probably drinking too little."
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