Drink at Least 8 Glasses of Water a Day - Really?

An interesting conclusion by Dr. Valtin, but I'll still try and chug
down at least 64 oz of water daily.

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For Release: August 8, 2002
Contact: DMS Communications (603) 650-1492

"Drink at Least 8 Glasses of Water a Day" - Really?

Dartmouth Professor Finds No Scientific Evidence for '8 x 8'

Hanover, NH -- It has become accepted wisdom: "Drink at least eight
glasses of water a day!" Not necessarily, says DMS physician Heinz
Valtin, MD. The universal advice that has made guzzling water a
national pastime is more urban myth than medical dogma and appears to
lack scientific proof, he found.

In an invited review published online by the American Journal of
Physiology August 8, Valtin, the Vail and Hampers professor emeritus
of physiology at Dartmouth Medical School, reports no supporting
evidence to back this popular counsel, commonly known as "8 x 8" (for
eight, eight-ounce glasses). The review will also appear in a later
issue of the journal.

Valtin, a kidney specialist and author of two widely used textbooks on
the kidney and water balance, sought to find the origin of this dictum
and to examine the scientific evidence, if any, that might support it.
He observes that we see the exhortation everywhere: from health
writers, nutritionists, even physicians. Valtin doubts its validity.
Indeed, he finds it, "difficult to believe that evolution left us with
a chronic water deficit that needs to be compensated by forcing a high
fluid intake."

The 8 x 8 rule is slavishly followed. Everywhere, people carry bottles
of water, constantly sipping from them; it is acceptable to drink
water anywhere, anytime. A pamphlet distributed at one southern
California university even counsels its students to "carry a water
bottle with you. Drink often while sitting in class..."

How did the obsession start? Is there any scientific evidence that
supports the recommendation? Does the habit promote good health? Might
it be harmful?

Valtin thinks the notion may have started when the Food and Nutrition
Board of the National Research Council recommended approximately "1
milliliter of water for each calorie of food," which would amount to
roughly two to two-and-a-half quarts per day (64 to 80 ounces).
Although in its next sentence, the Board stated "most of this quantity
is contained in prepared foods," that last sentence may have been
missed, so that the recommendation was erroneously interpreted as how
much water one should drink each day.

He found no scientific studies in support of 8 x 8. Rather, surveys of
fluid intake on healthy adults of both genders, published as
peer-reviewed documents, strongly suggest that such large amounts are
not needed. His conclusion is supported by published studies showing
that caffeinated drinks, such as most coffee, tea and soft drinks, may
indeed be counted toward the daily total. He also points to the
quantity of published experiments that attest to the capability of the
human body for maintaining proper water balance.

Valtin emphasizes that his conclusion is limited to healthy adults in
a temperate climate leading a largely sedentary existence - precisely,
he points out, the population and conditions that the "at least" in 8
x 8 refers to. At the same time, he stresses that large intakes of
fluid, equal to and greater than 8 x 8, are advisable for the
treatment or prevention of some diseases, such as kidney stones, as
well as under special circumstances, such as strenuous physical
activity, long airplane flights or hot weather. But barring those
exceptions, he concludes that we are currently drinking enough and
possibly even more than enough.

Despite the dearth of compelling evidence, then, What's the harm? "The
fact is that, potentially, there is harm even in water," explains
Valtin. Even modest increases in fluid intake can result in "water
intoxication" if one's kidneys are unable to excrete enough water
(urine). Such instances are not unheard of, and they have led to
mental confusion and even death in athletes, in teenagers after
ingesting the recreational drug Ecstasy, and in ordinary patients.

And he lists other disadvantages of a high water intake: (a) possible
exposure to pollutants, especially if sustained over many years; (b)
frequent urination, which can be both inconvenient and embarrassing;
(c) expense, for those who satisfy the 8 x 8 requirements with bottled
water; and (d) feelings of guilt for not achieving 8 x 8.

Other claims discredited by scientific evidence that Valtin discusses
include:
* Thirst Is Too Late. It is often stated that by the time people are
thirsty, they are already dehydrated. On the contrary, thirst begins
when the concentration of blood (an accurate indicator of our state of
hydration) has risen by less than two percent, whereas most experts
would define dehydration as beginning when that concentration has
risen by at least five percent.
* Dark Urine Means Dehydration. At normal urinary volume and color,
the concentration of the blood is within the normal range and nowhere
near the values that are seen in meaningful dehydration. Therefore,
the warning that dark urine reflects dehydration is alarmist and false
in most instances.

Is there scientific documentation that we do not need to drink "8 x
8"? There is highly suggestive evidence, says Valtin. First is the
voluminous scientific literature on the efficacy of the osmoregulatory
system that maintains water balance through the antidiuretic hormone
and thirst. Second, published surveys document that the mean daily
fluid intake of thousands of presumably healthy humans is less than
the roughly two quarts prescribed by 8 x 8. Valtin argues that, in
view of this evidence, the burden of proof that everyone needs 8 x 8
should fall on those who persist in advocating the high fluid intake
without, apparently, citing any scientific support.

Finally, strong evidence now indicates that not all of the prescribed
fluid need be in the form of water. Careful peer-reviewed experiments
have shown that caffeinated drinks should indeed count toward the
daily fluid intake in the vast majority of persons. To a lesser
extent, the same probably can be said for dilute alcoholic beverages,
such as beer, if taken in moderation.

"Thus, I have found no scientific proof that absolutely every person
must 'drink at least eight glasses of water a day'," says Valtin.
While there is some evidence that the risk of certain diseases can be
lowered by high water intake, the quantities needed for this
beneficial effect may be less than 8 x 8, and the recommendation can
be limited to those particularly susceptible to the diseases in
question.