From The Optimist Magazine
Fall/Winter 2016
If you find yourself confused about whether to drink eight glasses of water a day or twenty, chances are you’re overthinking it. There’s a perfect system that tells you when you need to drink: It’s called thirst.
By KARIN KLEIN
Dehydration has become a bogeyman of modern society, a condition to be feared as though it lurks on every street where we’re not carrying a bottle of water.
But we have a better way of making sure we’re hydrated than taking a gulp every couple of minutes or listening to unsubstantiated maxims about needing eight glasses, or even as much as two or three liters or more. Lucky for us, there’s a finely honed mechanism for ensuring that we get enough water.
And our bodies come equipped with it.
It’s called thirst.
“You need a system that tells you that you need water. You need a system that tells you how much and a system to get rid of it when there’s too much,” says Dr. Stanley Goldfarb, a kidney specialist and professor of medicine at the University of Pennsylvania who has become one of the nation’s foremost debunkers of water myths. “These are incredibly sophisticated systems.”
For a variety of reasons—in large part, marketing by bottled-water companies that charge a dollar or more for a drink we can get for nothing from the tap—we’ve come to mistrust these marvelous physical cues that have kept us going as a species for so many thousands of years. We’ve been told, despite an utter lack of scientific backing, that we need eight glasses of pure water a day or our skin will shrivel and our bodies will harbor toxins. And we’re convinced by the adage that if we wait until we’re thirsty to drink, we’ve already allowed ourselves to get dehydrated.
Well, that last statement is slightly true, Goldfarb says, if rather meaningless. The whole point of thirst is for the body to say, “Yep, there’s less water in here than there was a couple of hours ago, so let’s bring in more.” This is in no way damaging to us. Quite the opposite: It’s a sign that our bodies are responding to normal cues and acting to keep us well watered. A thirst mechanism that told us to drink when our bodies had no use for it would be pointless.
“If you’re thirsty, you have less water in your system than before you were thirsty,” he says. “It has a trivial impact. Your body is telling you that you’ve deviated from your baseline and you should have some water.”
Though many people still don’t realize it, scientists have known for years that the advice to down eight glasses of water every single day is bogus. A 2002 study concluded this after reviewing a wide body of literature on the subject. And as with most legends, the origin of this one is not entirely clear.
Drs. Rachel C. Vreeman and Aaron Carroll, professors of pediatrics at Indiana University School of Medicine, who have co-written three books intended to bust health myths, theorize that it came from a 1945 recommendation by the Food and Nutrition Board of the National Research Council. That report actually recommended 2.5 liters of water—more like 10 glasses a day—but the part people seemed to miss was that the council went on to say that most people get this through their food and any beverages they drink, whether for enjoyment or quenching thirst.
Another possible source, Vreeman and Carroll wrote in The BMJ in 2007, may have been Frederick Stare, who founded Harvard University’s nutrition department and recommended, without citing sources, drinking six to eight glasses of liquid a day. But then, Stare, who died in 2002, also recommended Coca-Cola as a “healthy between-meal snack.”
Others say two quarts was just an easy guideline for people to remember.
A more recent recommendation, published by the Institute of Medicine in 2004, called for even more water—2.7 liters for women and 3.7 liters for men—though it also said it was impossible to determine how much water people need to drink, and that almost everyone would be fine just letting thirst guide the whole process. But if that was the case, where did those hydration numbers come from? Goldfarb says it’s based on the average that people actually drink, not on any determination of need.
Some websites these days say you need an ounce of water per pound of body weight—a whopping 20 glasses a day for a 160-pound individual—or, for inactive people in temperate climates, half that. But again, the advice is repeated without references to scientific evidence.
There’s no doubt that severe dehydration is a serious matter—the kind of dehydration that causes people to stop or nearly stop urinating, that speeds up breathing and heart rate and lowers blood pressure, that causes confusion, irritability and sleepiness. Water is elemental to our very makeup. It’s what we are—about 66 percent of us, to be precise. People can survive several weeks without food, but the average human would have a tough time making it a week without water.
But except for endurance athletes and people working or playing for an extended period in very hot places, this is unlikely in healthy adults. Truly dark urine, significantly darker than apple juice, is generally a sign to take in some water, but that doesn’t mean people have to drink up extra cups to avoid anything darker than lemonade.
Yet the warnings about having too little water are everywhere, as are the supposed benefits of chugging extra pints. The moisture is good for your skin, keeping you young-looking, we’re told. It helps you lose weight. Drinking after massage supposedly will flush toxins out of your body. And we’re told it has to be pure water—coffee, tea and other beverages won’t do.
But a 2010 paper in Clinics in Dermatology found there was no evidence to support the good-skin adage, and Goldfarb says it makes no sense that drinking a couple of extra glasses of water would do much for your skin. “As the water is distributed through the body, only a few drops get to the face, and they soon leave,” he says.
There also are no studies to back up the idea that massage releases toxic substances that must be flushed away, or that drinking extra water will somehow cleanse our organs.
“If you have normal kidney function, you will get rid of the toxins your body produces each day, and you will excrete them,” he says.
When it comes to weight loss, the picture is more mixed. A 2015 study published in the journal Obesity found that obese people who were instructed to drink two glasses of water a half hour before mealtimes lost more weight over 12 weeks—two and a half pounds—than those who just tried to imagine that they were full. But this was a short-term study, and the authors cautioned that the results were preliminary and that the test group was limited to a particular demographic group. They also noted that previous studies hadn’t yet found much evidence for water as a diet aid.
“Daily water consumption is widely advocated as a useful tool to aid weight loss and is often included within weight-loss programs, yet there is little evidence to support this practice,” the authors wrote, echoing many other studies on hydration and weight loss.
The science couldn’t be clearer when it comes to another saying about hydration—that only pure water counts, and that coffee and tea are in fact dehydrating.
A 2014 study in the journal PLOS ONE found no difference in hydration between men who drank coffee and those who drank water, as long as the men were habitual coffee drinkers. And all fluids count: soda (though it’s not the healthiest choice), milk—even beer is mostly water. That’s not to mention the liquids in the food people eat, especially in diets rich in fruits and vegetables.
Meanwhile, studies that supposedly found that children are commonly dehydrated didn’t look at whether they showed clinical signs of dehydration, Goldfarb points out. Rather, researchers measured how concentrated their urine is, setting a level that strikes Goldfarb and other doctors as arbitrary—it’s never been accepted by clinicians as a dehydration marker.
It’s also worth keeping in mind, Goldfarb says, that some of the studies extolling the necessity of full hydration at every moment have been funded by the bottled-water industry.
With all this in mind, why do “eight glasses a day” and other water myths persist?
For one thing, Goldfarb says, much of the emphasis in health these days is centered around the belief that people have total control over their health and longevity, an idea that the public relishes. And the more they control, the healthier they believe they’ll be.
“The idea that your fluid intake doesn’t have any influence on your health is upsetting,” he says. “We like to think people get sick because of what they do to themselves. That’s the essence of the idea behind the flushing-toxins belief: you’re thinking you’re going to control the poisons in your body.”
Doctors don’t fight the misinformation because, unlike many other medical myths, this one is mostly benign.
But not entirely. It is possible to pour too much water into our bodies, with dangerous results. If hydration reaches the point where the kidneys no longer can effectively excrete the water, the blood vessels become oversaturated, throwing off the proportion of water to salt and other soluble substances. This potentially fatal condition is called hyponatremia.
This can become life-threatening when excess water starts entering other cells, which swell to accommodate it. In the brain, where cells are tightly encapsulated by the skull, that flexibility isn’t available. The resulting brain edema can lead to seizures, coma and death. Worsening matters, the symptoms of overhydration include fatigue, irritability and headache—some of the same symptoms that accompany dehydration. Misreading those cues can have dangerous consequences.
Though this is a rare occurrence, doctors are concerned that it might be becoming more common as long-distance runners and other athletes are urged to drink copious amounts of water to stay at peak performance. About one in eight marathon runners develop some level of potentially problematic overhydration, according to a 2005 paper in the New England Journal of Medicine. In 2007, a young California woman died after drinking six liters of water in three hours for a radio contest. Most people wrongly believe that water is one thing they can’t possibly overdo.
Still, just as most people aren’t in danger from lack of water, few are force-feeding gallons of extra water into their bodies every few hours. An extra couple of glasses isn’t going to hurt anyone. And some people do need to think consciously about taking in more water. The thirst cue appears to be somewhat depressed in elderly people, and extra water is known to help avoid the formation of kidney stones in people who are more prone to form them.
Perhaps the beliefs persist because people want hard-and-fast truths about medical science. Should they follow the Mediterranean diet? Do more cardio or lift more weights? Just how much water should they drink?
In this case, though, it all depends—on factors like the person’s physique, age, tendency to sweat, and consumption of water-laden foods. Climate plays a role, too. The best thing, government agencies and doctors concur, is to pay attention to your body.
If people are thirsty, or just enjoy drinking two to three quarts of water a day, by all means they should go ahead, Goldfarb and other doctors say. It’s another matter if they feel obligated to drag a bottle of water into every classroom and every meeting and down every sidewalk, and obsess about their urine being nearly clear.
“People schlepping around bottles of water is absurd,” Goldfarb says. “If they like it, that’s fine. But they should be aware: there’s a huge enterprise out there getting people to drink water. They make a lot of money selling bottled water.”
Modern society’s water craze is unnecessary and, when it involves buying bottled water, bad for our wallets and for the environment. Taken to an extreme, our hydration obsession can even be dangerous to our health.
