A new study out of Washington concludes that the long-held belief that people should drink eight glasses of water each and every day is, well, all wet.
Researchers with the Institute of Medicine of the National Academies hope their findings will dispel that water myth. Most healthy people will quench their body's thirst by drinking only when they're thirsty, they conclude.
The study measured total water intake, including clear water and beverages (which account for 80 per cent of intake) and foods, which account for the remaining 20 per cent. Lawrence Appel, chair of the Panel on Dietary Reference Intakes for Electrolytes and Water, says in a statement, "Our hydration needs can be met through a variety of sources in addition to drinking water." While water is a frequent choice for hydration, Appel notes, "people also get water from juice, milk, coffee, tea, soda, fruits, vegetables, and other foods and beverages."
Panel members have made general recommendations for water intake based on national data: women appear to be adequately hydrated by an average of 2.7 litres daily; men by 3.7 litres daily.
Dr. David Yeung, who is with the Department of Nutritional Sciences at the University of Toronto and is director of Corporate Nutrition for H.J. Heinz, agrees it is not wise to force -- or limit -- yourself to drinking eight glasses of water daily.
All of the body's organs require water to function, Dr. Yeung says, and without it, organs will shut down. A dehydrated body suffers an electrolyte imbalance and will feel dry, he says. Starting with thirst, symptoms to follow include a dry mouth and tight skin. As the dehydration progresses, he says, the result can be headache and a lack of concentration. "You'll feel tired and won't have that get-up-and-go," says Dr. Yeung. A person may feel a tingling sensation and experience hallucinations. Eventually, the blood will thicken, which can cause a stroke. "You can die," he cautions.
But Dr. Yeung warns that too much water is also unhealthy. "It flushes out the important vitamins and nutrients that you ingest that your body also needs to function, and it can actually thin the blood out to the point that the body cannot carry on its processes."
The eight-glasses-a-day rule is too general to apply to all, Dr. Yeung says. The body's required water intake depends on that person's ability to retain water, he explains. So those who urinate frequently or sweat a lot may need to replenish fluids more frequently than others.
"While one body's need for water differs from another, and those who physically work harder will probably need more water than those with sedentary jobs, a computer programmer still needs to drink throughout the day, just like a construction worker," Dr. Yeung says.
Steve Wallace, safety director for the Heavy Construction Safety Association of Saskatchewan, says the study's recommended water intake sounds a little much. But waiting until you're thirsty may not be the best idea because, by that time, "you're already dehydrated," Wallace says. "For optimum performance, you don't necessarily have to be chugging water, but you do want to continually take it in on a regular basis in small amounts."
No matter what the job is, he says, being dehydrated can be downright dangerous. "You're not alert, and you're putting yourself at risk, whether it's getting caught in a machine at the factory, or falling down the stairs at the office," Wallace adds.
Lydia Dumyn is a writer in Toronto.