The Eight-glasses Rule – How Much Water Should We Really Drink Daily?

Confused over the latest attempt to debunk a popular health myth about the need to drink eight glasses of water a day?

Dr. Aaron Carroll, a professor of Pediatrics at Indiana State University School of Medicine, is back in the spotlight about the need to drink water.

Back in 2007, he was co-author of a paper on medical myths, the first being that people should drink at least eight 8-ounce glasses of water a day. “It’s just not true,” he said, citing the fact there is no scientific evidence for the recommendation.

More recently, in an article written for the New York Times titled “No, You Do Not Have to Drink Eight Glasses of Water a Day,” the doctor once again is hoping to change people’s perceptions of that so-called rule.

“This paper got more media attention than pretty much any other research I’ve 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,” he wrote in the New York Times.

It is believed that the eight-glass rule originated from a Food and Nutrition Board recommendation back in the 1940s. For some reason, however, no one seemed to pay attention to the additional line noting that “most of this quantity is contained in prepared foods,” and the emphasis remained on filling up eight glasses and drinking them each day.

A Kidney Connection?

The pediatrician’s key concern now is over a study published in June by the American Journal of Public Health that found 54.5{06cf2b9696b159f874511d23dbc893eb1ac83014175ed30550cfff22781411e5} of children ages 6 to 19 were inadequately hydrated, at least by standards set in the study, which he states is causing undue concern for parents. The study set dehydration as a ‘urine osmolality’ of 800 mOsm/kg or higher. Carroll says that number is not concerning to most pediatricians he has spoken with, and he and others have never used urine osmolality to decide if a child is dehydrated.

“You don’t need to be a kidney specialist to know whether your child is dehydrated or when a parent needs to worry that their child is at risk for dehydration,” said Dr. John O’Reilly, a pediatrician at Baystate Children’s Hospital.

“There are some specific fluid replacement guidelines that we use in pediatrics, and they are generally based on a child’s weight and kidney function,” he added. “Even among scientists, there are still debates about how much fluid we should use and how much sodium we should give to children. Luckily, our kidneys and our body’s thirst mechanisms are pretty efficient regulators of how much fluids we should be taking in.”

Because infants, younger children, and children with developmental or communicative delays may not be able to tell someone that they are thirsty, parents should carefully monitor their intake of fluids and the frequency of their urination. If parents notice that their child is peeing less frequently than usual, or that their urine remains concentrated, dark, and smelly despite their drinking fluids, this may be a sign of dehydration, noted the Baystate pediatrician.

“Children have a higher proportional surface area than adults, and this means that they are at greater risk of losing fluids through sweating during hot summer days,” said O’Reilly, who stressed that parents should be talking to their pediatricians about how they should best protect their children from dehydration.

“The balance between water and salt is more delicate and complex in pediatric patients than in adults, so a simple saying such as ‘drink eight glasses of water a day’ should not be applied to all children and infants. The amount of water that is healthy for your child will vary by age and size, but I think water is almost always going to be a better choice for your child than juice or soda. Talk to your child’s pediatrician about healthy choices for what they should be eating and drinking to meet their nutritional and fluid needs,” he added.

Why Water?

So, why is water good for us — which should be part of the message — and how much water should we be drinking?

“Our cells are the building blocks of life and need water in order to function properly,” said Nancy Anderson, a pediatric dietitian from Baystate’s Food and Nutrition Services.

The Centers for Disease Control and Prevention (CDC) explains that water keeps body temperature normal, lubricates and cushions joints, protects the spinal cord and other sensitive tissues, and gets rid of wastes through urination, perspiration, and bowel movements. The body needs more water when someone is in a hot climate, more physically active than average, running a fever, or experiencing diarrhea or vomiting.

However, according to Anderson, there is no universally agreed upon figure as to how much water one needs daily. “The number varies whether adult or child and depends on various factors, such as your age, size, overall health, environment, and activity level.”

The Institute of Medicine notes that adequate fluid intake for adult men is about 3 liters of total beverages daily, while for women it is slightly less, at 2.2 liters. Again, this is a general guide, as is the slogan ‘drink eight 8-ounce glasses of water daily,’ which is equal to about 2 liters.

“Thirst is not a good indicator of hydration levels, especially the older we get, so it’s a good idea for adults to monitor their own urine frequency and color as they would for their children,” said Anderson. Other signs of dehydration in adults include dry mouth, weakness, dizziness, palpitations, confusion, and sluggishness.

While much of our fluid needs are met simply from water and other beverages consumed daily, Anderson said our bodies also get fluid from foods that we eat, such as most fruits and vegetables, which are high in water content.

To ensure that a child is getting enough water while in school, or even for an adult at work, Anderson suggests filling a freezer-safe water bottle (BPA-free) halfway overnight, then topping it off with water in the morning.

While some kids and adults don’t like the taste of tap water, Anderson suggests purchasing a Brita filtered pitcher for better taste, which can be filled from the sink and left in the fridge for all to pour a glass from. “It makes water taste so much better. It’s also a cheaper alternative and more environmentally sound than purchasing cases of water in plastic bottles, which can leach potentially harmful chemicals.”

How Much Is Too Much?

The American Council on Science and Health offers its own warning, noting that too much water consumption can actually be harmful or, if taken to the extreme, even deadly. The problem? Drinking too much, too quickly, can result in a dilution of the blood and a condition known as hyponatremia — a too-low concentration of sodium in the blood which in turn can be fatal.

Still, “hyponatremia is very rare. The kidneys generally do a great job at preventing this problem,” O’Reilly said.

The bottom line, Anderson said, is that, when kids or adults are thirsty, the best alternative is water over soda and other sugary drinks. Carroll agrees. And those who don’t read any further than the recent ‘eight-glasses-of-water-myth’ headlines are missing an important part of the message. v