Obey Your Thirst—and Ignore Advice to Over-hydrate
There’s a firmly entrenched belief that we all need to drink at least 64 ounces of fresh water daily. That’s in addition to any other sources of water one may consume throughout the day. Blame it on shoddy science reporting and the intractability of “common-sense medical advice” that sounds credible. But isn’t.
The notion that a specific minimal amount of water must be consumed every day is essentially misguided. Here’s why. The human body has sophisticated mechanisms to keep it properly hydrated. They range from “sensors” that indirectly monitor the relative water content of blood, to feedback mechanisms and hormonal controls that signal the kidneys and intestines, letting them know the body needs to conserve more—or less—water. The eight glasses myth is also predicated on another misunderstanding: Only water provides healthful hydration.
This is simply not true. Coffee or tea work fine. So do milk and other beverages. So does much of the food you eat. Getting plenty of fresh fruits and vegetables? Then you’re also getting water from these foods. It’s no stretch to imagine that eating watermelon may help with hydration, but it’s also true that there’s significant water in other, less-obvious foods. You may not view a cup of broccoli as a meaningful source of water. But your body does.
As it turns out, your body doesn’t care where its water comes from. Whether it’s from foods or supposedly “dehydrating” beverages, such as caffeinated coffee, your body will happily extract water from it and this will contribute to your daily need for water. And speaking of caffeine, unless you’ve never encountered it before, your kidneys will have adjusted to caffeine’s minor diuretic effect. So, if you’re a regular coffee drinker, you can set aside the notion that every cup you drink is dehydrating you. It’s not.
Of course, when it’s hot out, or you’re sweating a lot while working out, your need for water increases. But your body is perfectly capable of responding to this changing need, with little thought on your part. Your urine will become more concentrated, as less water is diverted by the kidneys to the bladder. You’ll get thirsty—and in response you’ll probably drink.
And that, say experts, is how athletes can avoid hyponatremia; the potentially dangerous condition characterized by low blood sodium levels. It’s caused by gorging on too much water, and it’s capable of killing. Simply listen to your thirst and trust that it will guide you to drink when you need hydration. You might think this advice arises from a desire to remind people to keep drinking plenty of water. But the opposite is true. Last summer, two high school football players died easily preventable deaths. From drinking too much water. Their bodies didn’t tell them to do it. They did it because they believed—or were told—it was necessary to avoid dehydration while working out in summer heat.
Drinking “beyond thirst” during exercise is hazardous to your health, experts warn. "Every single [exercise-associated hyponatremia] death is tragic and preventable,” said Tamara Hew-Butler, DPM, PhD, of Oakland University, Rochester, Mich. “If we just listen to our bodies and let go of the pervasive advice that if a little is good, then more must be better.”
Tamara Hew-Butler, Mitchell H. Rosner, Sandra Fowkes-Godek, Jonathan P. Dugas, Martin D. Hoffman, Douglas P. Lewis, Ronald J. Maughan, Kevin C. Miller, Scott J. Montain, Nancy J. Rehrer, William O. Roberts, Ian R. Rogers, Arthur J. Siegel, Kristin J. Stuempfle, James M. Winger, Joseph G. Verbalis. Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. Clinical Journal of Sport Medicine, 2015; 25 (4): 303 DOI: 10.1097/JSM.0000000000000221