Washington "Drink at least eight glasses of water a day" is an adage some obsessively follow, judging by the people sucking on water bottles at every street corner. But the need for so much water may be a myth.
So says a scientist who undertook an exhaustive hunt for evidence backing all this water advice and came up mostly, well, dry. Now the group that sets the nation's nutrition standards is studying the issue, too, to see if it's time to declare a daily fluid level needed for good health and how much leaves you waterlogged.
Until then, "obey your thirst" is good advice, says Dr. Heinz Valtin, professor emeritus at Dartmouth Medical School, whose review of the eight-glass theory appears in this month's American Journal of Physiology.
It's about time for all the attention, says Pennsylvania State University nutritionist Barbara Rolls, a well-known expert on thirst. "There's so much confusion out there."
Much of it centers on where you should get your daily water.
"There's this conception it can only come out of a bottle," and that's wrong, notes Paula Trumbo of the Institute of Medicine's Food and Nutrition Board, which hopes to decide by March whether to issue the first official water-intake recommendation.
In fact, people absorb much water from the food they eat. Fruits and vegetables are 80 to 95 percent water; meats contain a fair amount; even dry bread and cheese are about 35 percent water, Rolls says. That's in addition to juices, milk and other beverages.
And many of us drink when we don't really need to, spurred by marketing, salty foods and dry environments, Rolls says.
"For most of us, that's not going to matter you're just going to need to go to the bathroom more," she says.
While working on his review, Valtin couldn't find any research proving the average person needs to drink a full 64 ounces of water daily.
So how much do we need?
Until the Institute of Medicine sets a level, "if people obey their thirst and they are producing urine of a normal yellow color, that's a safe sign," Valtin concludes.