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Department of Physiology, Dartmouth Medical School, Lebanon, New Hampshire 03756
Despite the seemingly
ubiquitous admonition to "drink at least eight 8-oz glasses of water
a day" (with an accompanying reminder that beverages containing
caffeine and alcohol do not count), rigorous proof for this counsel
appears to be lacking. This review sought to find the origin of this
advice (called "8 × 8" for short) and to examine the
scientific evidence, if any, that might support it. The search included
not only electronic modes but also a cursory examination of the older
literature that is not covered in electronic databases and, most
importantly and fruitfully, extensive consultation with several
nutritionists who specialize in the field of thirst and drinking
fluids. No scientific studies were found in support of 8 × 8. Rather, surveys of food and fluid intake on thousands of adults of both
genders, analyses of which have been published in peer-reviewed
journals, strongly suggest that such large amounts are not needed
because the surveyed persons were presumably healthy and certainly not
overtly ill. This conclusion is supported by published studies showing
that caffeinated drinks (and, to a lesser extent, mild alcoholic
beverages like beer in moderation) may indeed be counted toward the
daily total, as well as by the large body of published experiments that
attest to the precision and effectiveness of the osmoregulatory system
for maintaining water balance. It is to be emphasized that the
conclusion is limited to healthy adults in a
temperate climate leading a largely sedentary existence, precisely the population and conditions that the "at least" in 8 × 8 refers to. Equally to be emphasized, lest the message of this review be misconstrued, is the fact (based on published
evidence) that large intakes of fluid, equal to and greater than 8 × 8, are advisable for the treatment or prevention of some diseases
and certainly are called for under special circumstances, such as
vigorous work and exercise, especially in hot climates. Since it
is difficult or impossible to prove a negative
in this instance, the
absence of scientific literature supporting the 8 × 8 recommendationthe author invites communications from readers who are
aware of pertinent publications.
fluid intake; optimal fluid intake; daily water intake; water balance
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