The warmer weather and longer days have inspired reminders to “stay hydrated” and drink eight glasses of water – or about two liters – a day.
Not to burst anyone’s water bottle, but healthy people can actually die from drinking too much water. I am an exercise physiologist, and my research focuses on overhydration and how drinking too much water affects the body. Since water – and sodium – balance is essential to life, it is extremely rare for people to die from drinking too much – or too little – fluid. In most cases, your body’s finely tuned molecular processes are unconsciously taking care of you.
Water out, water in
As spring unfolds, hydration challenges take root across schools, sports, and workplaces. These heavily marketed hydration challenges serve to cultivate both camaraderie and friendly competition to ensure that we drink compulsory amounts of water throughout the day.
Hydration and “Gallon Challenges” support the widely held belief that water consumption beyond physiological need – or thirst – is healthy.
But this is not so. Individual body water needs – intake – are primarily based upon how much water people lose. How much water each person needs to drink mainly depends on three factors:
- Body weight. Bigger people need more water.
- Environmental temperature. When it’s hotter, people sweat and lose water.
- Physical activity levels. Increased exercise intensity increases sweat water losses.
Therefore, a “one size fits all” fluid replacement strategy, such as drinking eight glasses of eight ounces of water per day, is inappropriate for everyone.
It remains unclear where the “8 x 8” water intake recommendation comes from. Perhaps, this two-liter intake threshold is derived from a misinterpretation of original recommendations offered by the U.S. Food and Nutrition Board in 1945 as well as the 2017 European Food Safety Authority, which states the daily recommended amount of water includes all beverages plus the moisture contained in foods.
This means that the moisture contained in foods, especially fresh fruits, sodas, juices, soups, milk, coffee and, yes, even beer, contributes to this daily recommended water requirement. These guidelines go on to suggest that most of the recommended water content can be accomplished without drinking additional cups of plain water.
And, it is important to note that while alcohol has diuretic properties – ethanol acts directly on the kidneys to make us pee more – caffeinated beverages, like tea and coffee, do not increase urinary water losses above the amount of water contained in these beverages.
Now, you may be wondering why this is so. After all, you’ve heard from a lot of people that you need to drink more, more, more.
Because total body water…