“Drink at least eight glasses of water a day.” Really? Is there scientific evidence for “8 × 8”?

Abstract

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 sedentaryexistence, 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 recommendation—the author invites communications from readers who are aware of pertinent publications.

Do Patients Drink Enough Water? Actual Pure Water Intake Compared to the Theoretical Daily Rules of Drinking Eight 8-Ounce Glasses and Drinking Half Your Body Weight in Ounces

“…glasses a day. Even if the old adage of drinking 8 glasses of water a day were scientifically verified, which it is not [25], most of our patients would be well deficient. When we assessed how much water our patients should be drinking based on the theoretical rule of drinking half your body weight in ounces, we determined that most patients were again deficient, but even more so then going by the 8 glasses a day rule.…”

“…As we suggested earlier, we believe the guideline of drinking half body weight in ounces would be more hydrating than the 8 glasses a day rule. Just as the 8 × 8 rule has unknown precise origins [25], the half body weight rule also has unknown origins, let alone being scientifically validated (we were unable to locate any documentation). There may be concerns, however, for the 1/2BW rule when it comes to larger massed individuals.…”

“…Critics of drinking extra water, beyond that from being thirsty often suggest that people will drink as much as they need, as the perception of thirst will guide their intake [25] [28]. However, physiologically, there are body indicators suggesting dehydrating effects have occurred before the feeling of thirst is perceived.…”

“…The old adage, "drink eight glasses of water a day" ("8 × 8") has no scientific merit [25]. How can a 100 lb female and a 250 lb male have the same water requirements?…”

Diabetes insipidus: the basic and clinical review

“…ADI is mainly caused due to the disturbance of thirst center 44 while the psychiatric disorders and psychiatric medications are important in PDI. 46,48,49 The side effects of psychiatric medications play an important role in PDI because these medications cause the dryness of mouth leading to high fluid intake. PP can also be due to some behavioral causes.…”