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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. DMS news is on the web at http://www.dartmouth.edu/dms/news. ScienceDaily.com
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