Here's something to think about: More than half of your body is made up of water. Not fat, not muscleÃ¢â‚¬”H2O.
So if you weigh, say, 150 pounds, about 90 of them come from the liquid stuff. In fact, every one of your cells is essentially a soggy bag of fluid, surrounded by more fluid. Without it, your cellsÃ¢â‚¬”and youÃ¢â‚¬”would die. That's why people can survive a long while without food but not without water, the single most vital substance for sustaining life.
If this all seems dramatic, consider that hydration is key for keeping your digestion on track, your nasal passages moist, and your kidneys content. And for enhancing pretty much all of your major organs, including the brain.
The Delivery System
You might now be picturing your insides as a bunch of parts just sloshing around in water. A more accurate picture involves some complex biology: Every time you take a sip of H2O, it seeps through your intestines into your blood vessels and, like a bucket of water dumped into the ocean, becomes part of a larger mix of liquid and mineralsÃ¢â‚¬”most notably, salt.
This saline-type solution shuttles chemical signals back and forth between cell membranes, informing your every action. It also ferries around your body's other must-haves (oxygen, glucose, hormones) via the blood, which is mostly made up ofÃ¢â‚¬”you guessed itÃ¢â‚¬”water.
How and when water exits your body depends on myriad factors, including humidity and temperature, your activity level, and how much you sweat, says Lawrence Armstrong, Ph.D., a researcher in the Human Performance Laboratory at the University of Connecticut. What is clear is that if too much exits and not enough enters, your well-being can start to suffer.
Given all of the above, it may seem you have plenty of water to spare. But losing even a tiny amount can set off an alarm. ThirstÃ¢â‚¬”a dehydration warning sign, assuming you haven't just had a salty snackÃ¢â‚¬”typically kicks in when you've lost a measly 2 percent of your water weight.
At that point, you could become prone to muscle cramps and headaches. Your athletic abilities might start to falter. The resulting stress speeds up your heartbeat and can leave you feeling fatigued, says Lawrence L. Spriet, Ph.D., chair of human health and nutritional sciences at the University of Guelph in Ontario.
In short, everything begins to feel like a slog. And if you rarely remember to sip water throughout the day, beware: Long-term low liquid intake has been linked to problems such as kidney stones and urinary-tract infections, as well as prolonged labor if you're pregnant.
An H2O deficiency can also affect the brain in surprising ways. Research suggests that mild dehydrationÃ¢â‚¬”which may not even make you thirstyÃ¢â‚¬”can interfere with your ability to concentrate and can ramp up stress and anxiety. Scientists are still figuring out the particulars, but they suspect a lack of water adversely affects the nerve cells that control mood.
Of course, being really dehydrated is very serious. If you lose 5 to 6 percent of your water weight at one time, you could suffer symptoms such as mental confusion or vomiting, says Stella L. Volpe, Ph.D., R.D., professor and chair of the nutrition sciences department at Drexel University. (This type of severe dehydration, which usually affects only athletes and those in extreme climates, should be considered an ER-worthy medical emergency.)
The tricky thing is, there are few set-in-stone guzzling guidelines. Turns out, the oft-heard "eight glasses a day" may be a health myth that won't work for every person; it all depends on individual biology and lifestyle.
In general, the Institute of Medicine recommends that the average woman get at least 11.4 cups of water a day, though that includes fluid you get from food (even cooked chicken, for example, is filled with water, making it likely you'll eat around 20 percent of your daily H2O intake).
The American College of Sports Medicine recommends pre-hydrating, or drinking about 16 ounces of water four hours before you exercise. Better yet, stay hydrated by sipping slowly throughout the day. Slurping down huge amounts right before hitting the gymÃ¢â‚¬”or, say, getting on a long flightÃ¢â‚¬”mostly just means extra trips to the bathroom, says Hannah Davis, a certified personal trainer and cofounder of Gotham Versatile Training in New York City.
When in doubt, stop and ask yourself, What activity am I doing, for how long, and in what temperature? If you're exercising for less than an hour in cool weather, you probably don't need to drink water throughout your workout. If you're getting in a fierce sweat sessionÃ¢â‚¬”say, a tennis tournament or longer runÃ¢â‚¬”pause for fluid breaks. If you're at the office and just wondering about the sogginess of your cells, take a peek at your urine, says Volpe. If it's pale yellow, you're fine. Any darker means you need more water; consistently crystal-clear urine means you're trying too hard to hydrate.
Above all, listen to what your body asks for. A recent article in the British Medical Journal suggests that while the sports-drink industry has raised loud alarms over dehydration, people should simply respond to their own symptoms. Therein lies the only hard rule of hydration: If you're thirsty, drink. And if you've gone a few hours without sipping, take down a glass of water.
When Water Becomes Poison
Just as it's possible to become dangerously dehydrated, you can become over-hydrated. An excess of H2O means your cells can't function properly, and your kidneys can't work fast enough to get rid of the stuff. But before you start worrying, know this: Water intoxication is very rare and is typically only a hazard for ultramarathoners and those who over-drink while exercising for hours at a stretch. (Everyone else can monitor their pee: If it's always totally clear, cut back on your sipping.)