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Benefits of Drinking Water
No, You Do Not Have to Drink 8 Glasses of Water a Day
Benefits of Drinking Water Oversold?
But there is nothing magical about those eight glasses, at least when it comes to proven health benefits, according to a new report. "There is no clear evidence of benefit from drinking increased amounts of water," writes Stanley Goldfarb, MD, professor of medicine at the University of Pennsylvania, Philadelphia, and the senior author of an editorial on the topic in the Journal of the AmericanSociety of Nephrology.
On the other hand, he adds, "There is also no clear evidence of lack of benefit." There's a general lack of evidence either way.
Those doctors and others who have been recommending drinking eight glasses of water aren't basing it on anything scientific, according to Goldfarb. He concludes that most healthy people don't have to worry about drinking eight glasses every day.
He emphasizes he is talking about healthy people with kidneys that function well. And he points out that people who live in hot, dry climates do need to drink more water to avoid dehydration, as do those who engage in vigorous exercise.
(How much water do you drink each day? What other liquids?
Health Benefits of Drinking Water: Search for Evidence
Goldfarb was curious about where the longstanding recommendation about eight daily glasses of water originated. "In my mind it wasn't that drinking this extra water would hurt you, but that you might not have to."
So he combed through medical literature dating back to the early 1970s, trying to find the science to back up the advice.
Turns out, there is no single study and no single outcome that led to the recommendation becoming popular, he says. Somehow, it took on a life of its own.
Goldfarb and his University of Pennsylvania colleague, Dan Negoianu, MD, next examined some popular claims about the health benefits of drinking water, trying in each case to find scientific evidence.
"We looked at the evidence of some of the so-called urban myths that have grown up about drinking water," Goldfarb says.
Claim No. 1: Drinking Water Helps Excrete Toxins. Drinking lots of water is widely thought to help improve kidney function and boost the clearance of toxins. One way it could do this, Goldfarb says, is by a mechanism called glomerular filtration, a measure of the kidney's ability to filter and remove waste products.
But in one study the researchers looked at, increased water intake by 12 young and healthy people actually decreased their glomerular filtration rate. And in another study, the rate did not change over time during a six-month period in which older men drank more water to try to improve bladder function.
In other research, increased water intake was found to affect the clearance of many substances by the kidneys, including sodium. But the studies don't prove any sort of clinical benefit, Goldfarb says.
"What almost certainly happens is, any toxins the kidney is responsible for excreting simply get diluted when the person is drinking a lot of water," Goldfarb says.
Claim No. 2: Drinking Water Helps Your Organs Work Better. Water is retained in various organs, so the thinking goes, and they work better with more water in them.
But Goldfarb and Negoianu say how much water is retained varies with the speed with which the water is taken in. If it's sipped, it's more likely to stay in the body than when gulped.
Even so, they could find no studies documenting that increased water intake helped the organs.
Claim No. 3: Drinking Water Reduces Food Intake and Helps You Lose Weight. Drinking more water is widely encouraged to help weight loss, the theory being that the more water you drink, the fuller you will feel and the less you will eat. "The [medical] literature on this is quite conflicted," Goldfarb says.
"Drinking before a meal might decrease intake [according to one study], but another study found [it did] not."
Even so, Goldfarb calls this claim one of the most promising for further study.
Claim No. 4: Drinking Water Improves Skin Tone. "From a quantitative sense, this doesn't make sense," Goldfarb says. The water you drink will be distributed throughout the body. "Such a tiny part of it would end up in the skin," he says.
"It turns out one small study showed there might be an increase in blood flow in those who drink [a lot of] water, but no one has ever looked scientifically [to see if it improves skin tone]."
Claim No. 5: Drinking Water Wards Off Headaches. Headache sufferers often blame water deprivation. But Goldfarb could only find one study that looked at this. The study participants who boosted their water intake had fewer headaches than those who did not, but the results were not statistically significant, meaning they could have been chance findings.
Second Opinion: Health Benefits of Drinking Water
The report provides interesting -- and sometimes surprising -- information, says David Baron, MD, a family physician and chief of staff at Santa Monica-UCLA Medical Center & Orthopaedic Hospital, Calif., who reviewed it for WebMD.
The most surprising finding, he says, was the lack of a scientific link found between drinking a lot of water in order to eat less. "I thought [the suggestion that] filling up your stomach with water might help lose weight makes sense," he says.
The report isn't dismissing the need to drink a healthy amount of fluids, he says. It simply showed no scientific basis to the recommendation to drink eight glasses of water daily.
"There is a lot of individual variation" in exactly how much water or fluid people need," he says.
Most of us, he says, are OK "by trusting our instincts" about how much to drink. "If you have a normal heart, normal kidneys, and normal thirst mechanism, it's not likely you will get dehydrated if there is a sufficient supply of fluids available," he says, and drink when thirsty.
Drinking Water: A Placebo Effect?
Might drinking a lot of water make us think we feel better, look better, and function better? Could there be a placebo effect to those eight daily glasses?
"I'm certain there is," Goldfarb says. "The placebo effect is very strong."
And if you're still convinced lots of water does your body good?
No problem. "People say they feel stronger and healthier if they
drink more water," he says. "That's fine. If they enjoy that benefit,
so be it. [But] those who don't feel that way shouldn't feel
obligated to drink the eight glasses."
No, You Do Not Have to Drink 8 Glasses of Water
Its just not true. There is no science behind it.
And yet every summer we are inundated with news media reports warning that dehydration is dangerous and also ubiquitous.
These reports work up a fear that otherwise healthy adults and children are walking around dehydrated, even that dehydration has reached epidemic proportions.
Lets put these claims under scrutiny.
I was a co-author of a paper back in 2007 in the BMJ on medical myths. The first myth was that people should drink at least eight 8-ounce glasses of water a day. This paper got more media attention (even in The Times) than pretty much any other research Ive ever done.
It made no difference. When, two years later, we published a book on medical myths that once again debunked the idea that we need eight glasses of water a day, I thought it would persuade people to stop worrying. I was wrong again.
Many people believe that the source of this myth was a 1945 Food and Nutrition Board recommendation that said people need about 2.5 liters of water a day. But they ignored the sentence that followed closely behind. It read, Most of this quantity is contained in prepared foods.
Water is present in fruits and vegetables. Its in juice, its in beer, its even in tea and coffee. Before anyone writes me to tell me that coffee is going to dehydrate you, research shows thats not true either.
Although I recommended water as the best beverage to consume, its certainly not your only source of hydration. You dont have to consume all the water you need through drinks. You also dont need to worry so much about never feeling thirsty. The human body is finely tuned to signal you to drink long before you are actually dehydrated.
Contrary to many stories you may hear, theres no real scientific proof that, for otherwise healthy people, drinking extra water has any health benefits. For instance, reviews have failed to find that theres any evidence that drinking more water keeps skin hydrated and makes it look healthier or wrinkle free. It is true that some retrospective cohort studies have found increased water to be associated with better outcomes, but these are subject to the usual epidemiologic problems, such as an inability to prove causation. Moreover, they defined high water consumption at far fewer than eight glasses.
Prospective studies fail to find benefits in kidney function or all-cause mortality when healthy people increase their fluid intake. Randomized controlled trials fail to find benefits as well, with the exception of specific cases for example, preventing the recurrence of some kinds of kidney stones. Real dehydration, when your body has lost a significant amount of water because of illness, excessive exercise or sweating, or an inability to drink, is a serious issue. But people with clinical dehydration almost always have symptoms of some sort.
A significant number of advertisers and news media reports are trying to convince you otherwise. The number of people who carry around water each day seems to be larger every year. Bottled water sales continue to increase.
This summers rash of stories was inspired by a recent study in the American Journal of Public Health. Researchers used data from the National Health and Nutrition Examination Survey from 2009 to 2012 to examine 4,134 children ages 6 to 19. Specifically, they calculated their mean urine osmolality, which is a measure of urine concentration. The higher the value, the more concentrated the urine.
They found that more than half of children had a urine osmolality of 800 mOsm/kg or higher. They also found that children who drank eight ounces or more of water a day had, on average, a urine osmolality about 8 mOsm less than those who didnt.
So if you define dehydration as a urine osmolality of 800 mOsm/kg or higher, the findings of this study are really concerning. This article did. The problem is that most clinicians dont.
Im a pediatrician, and I can tell you that I have rarely, if ever, used urine osmolality as the means by which I decide if a child is dehydrated. When I asked colleagues, none thought 800 mOsm/kg was the value at which theyd be concerned. And in a web search, most sources I found thought values up to 1,200 mOsm/kg were still in the physiologically normal range and that children varied more than adults. None declared that 800 mOsm/kg was where wed consider children to be dehydrated.
In other words, theres very little reason to believe that children who have a spot urine measurement of 800 mOsm/kg should be worried. In fact, back in 2002, a study was published in the Journal of Pediatrics, one that was more exploratory in nature than a look for dehydration, and it found that boys in Germany had an average urine osmolality of 844 mOsm/kg. The third-to-last paragraph in the paper recounted a huge number of studies from all over the world finding average urine mOsm/kg in children ranging from 392 mOsm/kg in Kenya to 964 in Sweden.
That hasnt stopped more recent studies from continuing to use the 800 mOsm/kg standard to declare huge numbers of children to be dehydrated. A 2012 study in the Annals of Nutrition and Metabolism used it to declare that almost two-thirds of French children werent getting enough water. Another in the journal Public Health Nutrition used it to declare that almost two-thirds of children in Los Angeles and New York City werent getting enough water. The first study was funded by Nestlé Waters; the second by Nestec, a Nestlé subsidiary.
Its possible that there are children who need to be better hydrated. But at some point, we are at risk of calling an ordinary healthy condition a disease. When two-thirds of healthy children, year after year, are found to have a laboratory value that you are labeling abnormal, it may be the definition, and not their health, that is off.
None of this has slowed the tidal push for more water. It has even been part of Michelle Obamas Drink Up campaign. In 2013, Sam Kass, then a White House nutritional policy adviser, declared 40 percent of Americans drink less than half of the recommended amount of water daily.
There is no formal recommendation for a daily amount of water
people need. That amount obviously differs by what people eat, where
they live, how big they are and what they are doing. But as people in
this country live longer than ever before, and have arguably freer
access to beverages than at almost any time in human history,
its just not true that were all dehydrated.
Note to the author on 8/25/15. "I read your report "No, You Do Not Have to Drink 8 Glasses of Water a Day". I found a lot of examples on unnecessary levels of water consumption. Did I miss, in your 1,200 words, your opinion of what consumption level would generally be acceptable? Granted, people need to know what companies like Nestle are doing. However, just to complain about something without giving an alternative I find equally unethical. So, what is your recommendation?"
Water, water, everyone.../Nor any drop to drink. - Samuel Taylor Cloeridge
(Editor's noter:Whaat with industrial and agricultural pollution, his words are more of a prediction than he ever imagined.)