Don’t panic if you’re not drinking multiple glasses
Most of us have heard the folk wisdom that to stay healthy we need to drink eight 8-ounce glasses of water a day. By now, many of us know that the so-called 8X8 rule is a myth. Yet, in spite of wide debunking by scientists and health professionals, claims persist that downing litres of water daily is necessary to keep us properly hydrated.
The origin of the myth may date back almost a century to 1921 when a scientist measured all the fluids he lost in a day to sweating, breathing and urinating––about eight cups or 1.9 litres. The more commonly cited source is the 1945 American study by the Food and Nutrition Board, National Academy of Sciences that put our daily intake at about 2.5 litres.
Canada’s Food Guide simply does not provide any specifics when it comes to healthy water intake. The Health Canada website explains why. “A review of data on water needs was conducted as part of the Dietary Reference Intake process. It was found that a wide range of intakes are compatible with normal hydration, and thus a specific requirement could not be set.”
Here’s the thing. That American study at the root of the myth went on to say of the need for water, “Most of the quantity is contained in prepared foods.” Health Canada’s website says, “Many foods and beverages are sources of water and no one source is essential for normal physiological function and health. Plain drinking water is promoted in the Food Guide as a calorie-free way to respond to thirst.” In other words, our bodies may or may not need 8X8 glasses of water every day, but we don’t have to drink that much pure water or, any water at all, to get it.
The researcher who uncovered the origins of the myth in 2001, Dr. Heinz Valtin, went on to say that he could find no scientific evidence to support the popular claim that we need to drink so much pure water to stay healthy. While drinking water is a great way to get the daily requirement of fluids, there is nothing wrong with most alternative sources. Fruits and vegetables, juices, milk, soup, and even meats can provide all the water we need.
Nutritionist Ann Grandjean of the Center for Human Nutrition in Omaha has conducted several studies that tackle some of water’s most enduring myths. In “The Effect on Hydration of Two Diets, One with and One without Plain Water” from 2002, she and her co-authors determined that drinking other liquids keeps us just as hydrated as water. “Inclusion of plain drinking water compared to exclusion of plain drinking water in the diet did not affect the markers of hydration used in this study,” conclude the authors.
There’s a part two to this myth, that because of their effect on the body, caffeinated drinks like tea and coffee may work to dehydrate us even though they are mostly water. That’s because the diuretic effect of caffeine results in a net loss of fluids from the body, according to this part of the myth.
Angela Dufour is a registered dietitian and sports dietitian at Nutrition in Action, Halifax. She says that large amounts of caffeine, for example from excessive coffee consumption (more than three cups a day) or energy drinks, which she says to avoid because they are often full of sugar and have no benefits at all, can result in a net loss of water.
As for alcohol, drinks like beer can count as healthy fluid intake. Still, many of us have had the experience of waking up thirsty after one too many. Research does demonstrate that too much alcohol dehydrates our bodies. Grandjean writes that alcohol is the only common drink that can produce a net loss of water in the body, but it usually takes more than one serving of alcohol to produce noticeable dehydration.
So, if the 8X8 rule is a myth and water from other sources when taken in moderation keeps us sufficiently hydrated, how much water do we need in our diet? How do we know when we need it, and how do we know when we are getting enough?
Dufour works with athletes. She says that fluid intake requirements depend on a large number of factors and vary widely from person to person, including activity and perspiration levels (especially for athletes), climate and daily temperature, illness and fever, season and altitude, gender, age, weight and personal metabolism levels.
“There are so many factors involved, it’s never a constant,” says Dufour of our fluid needs. “There is no specific rule per individual.” She suggests that even relying on our own thirst mechanism is problematic because when we feel thirsty, we might already be slightly dehydrated. This is especially true for seniors, children and athletes. As a sports nutritionist, Dufour says knowing when and how much to drink, “becomes a real science.”
For ordinary people, she says that dehydration causes recognizable symptoms. “If you’re feeling weak or dizzy with muscle cramps, low blood pressure, constant confusion and lack of concentration,” you could be clinically dehydrated. She sees these symptoms with some of her clients and works with them to predict the amount of fluids they’ll need, given variables like activity level and temperature.
For the rest of us, Dufour says, “It’s good to get in tune with your own body and know your own hydration variables and how much that can differ from day to day.” She says one of the easiest general indicators of healthy fluid intake is urine colour. “A nice, pale lemon juice colour is the perfect level of hydration.”
While we need water to survive, except in a few special circumstances like the treatment of kidney stones, research demonstrates that drinking extra water provides few, if any additional health benefits. At the same time, water is a great beverage. Drinking water instead of sugary beverages is likely to reduce the risk of dental decay and obesity. Tap water as a replacement for pop and other sweet drinks is also easy on the wallet.