For a long time, we've been led to believe we need to drink 8 cups of water a day, but “this number doesn’t come from any research,” says Riana Pryor, who specializes in heat and hydration research at the Korey Stringer Institute at the University of Connecticut. And although First Lady Michelle Obama’s new message urging Americans to drink more water is a good one for many reasons, no federal guidelines actually exist telling us how much water we should be drinking.
The latest guidelines from the Institute of Medicine recommend that most women consume about 91 ounces—that’s actually about 9 cups of total water a day. Men need a bit more; about 125 ounces (or 13 cups) a day. But there's good news: that total includes other beverages (like coffee, tea, soda and milk) as well as foods (for example, one medium apple translates to about 6 ounces of fluid).
Since water makes up more than two-thirds of the weight of the human body, staying hydrated is important for a few reasons. Water lubricates and cushions your joints, protects your spinal cord and other sensitive tissues, and transports wastes from your body through perspiration, urination, and bowel movements. Being hydrated helps with memory and cognition; it also helps to improve your mood and immune function.
In terms of how much you really need, it depends on your size, weight, age, activity level, and more. Both children and adults over 50 have thirst mechanisms that are behind the normal healthy population. The danger? You might be slower to recognize thirst and thus be at more risk of becoming dehydrated (especially children, who lose water through increased activity and sweat). A helpful reminder to stay hydrated: keep some water within reach whenever possible and take frequent sips throughout the day.
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For normal healthy adults, thirst is an excellent indicator of your hydration needs. Although we’ve been told for years that by the time you’re thirsty you’re already dehydrated, “if you’re not thirsty, it usually means you have enough water in your system,” she says. You’ll begin to feel thirst when you’re about two percent dehydrated (this amount of dehydration is not harmful to the body). This is a good indicator that it’s time to drink water, “or else you will become more dehydrated and start to see changes in mood, fatigue, and performance,” says Pryor.
But there are exceptions to this rule: People who exercise a lot need more water; so do people who live or work in hot climates. What’s more, if you take multiple medications or rely on certain drugs like diuretics, antihistamines, and some psychiatric prescriptions, your hydration needs might be greater than the average person’s. It’s always best to check in with your pharmacist or healthcare provider.
How do you know when you’re getting enough? Check your urine. If it’s pale (like lemonade), you are in good shape. But if it’s dark (like apple cider), you need to up your intake of fluids.
Certain illnesses and health conditions require you to drink more water; among them fever, vomiting or diarrhea, bladder infections, and urinary tract stones. On the other hand, conditions like heart failure or certain forms of kidney, liver, and adrenal diseases that have an effect on water excretion may require you to limit your intake of fluids.
Also important to consider is how much salt you eat, says registered dietitian Danielle Omar, M.S., R.D., a nutritionist in the Washington, D.C. area. Someone eating a diet high in sodium will need more water, she says. So will a person whose diet doesn’t include fresh fruits and vegetables, which can contain a good amount of water.
Taking a lot of medications without drinking enough water could put a strain on your kidneys, whose job it is to remove waste from the blood. Water helps to flush out these wastes (another plus is that it can lower your chances of getting kidney stones and infections).
For instance, if you take over-the-counter or prescription painkillers containing ibuprofen (Advil, Motrin), naproxen (Aleve) or acetaminophen (Tylenol), it’s advisable to wash them down with a large glass of water to help eliminate the drug from your kidneys.
Although water is the first thing many of us think of when we hear “hydration,” foods like watermelon, carrots, grapes, cucumbers, and spinach have very high concentrations of water – over 90 percent, says Pryor. And the added bonus is that you’re also getting health benefits like fiber, vitamins, and minerals.
Coffee or tea, juice, soda, and sports drinks count, too: but beware of extra calories. Regular soda, energy or sports drinks, and other sweet drinks usually have a lot of added sugar (for instance, substituting water for one 20-ounce, sugar-sweetened soda will save you about 240 calories). You’re better off sipping water or other drinks that have few or no calories. “Mrs. Obama’s real message to drink more water is hoping to encourage people to switch from their sugary beverages to water,” thus fighting obesity, says Pryor.
What about caffeine? While the caffeine in some energy drinks, coffee, and tea might have a mild diuretic effect, Omar says, studies do not show they increase the risk of dehydration.
There’s no evidence that you’re safer drinking bottled water over tap; in fact just because water comes from a bottle, there’s no assurance it’s any cleaner or safer than tap water, according to some studies from environmental groups. An estimated 25 percent or more of bottled water is simply tap water, which is sometimes treated, but oftentimes is not.
There is such a thing as drinking too much water – and it can, in extreme cases, be life threatening because the level of sodium in your blood becomes diluted, causing your cells to swell. Known as hyponatremia, or “water intoxication,” its symptoms include headache, confusion, fatigue, and irritability. It’s very rare among the average population (usually, stomach fullness will stop individuals from continuing to consume more water than they need) and most common among marathon runners or extreme athletes, who sometimes overestimate the amount of water they really need.
Our bodies might be good at reading a lot of cues, but they are not always expert at knowing the difference between hunger and thirst. “A lot of people think they’re hungry because their stomach doesn’t feel full,” says Pryor, but sometimes if you drink water the hunger disappears.
Many experts advise that people who think they’re hungry to drink a full glass of water and wait a few minutes to see if the desire to chow down goes away.
Can drinking water actually help contribute to weight loss? It may be possible for some: A study published in the journal Obesity says that in overweight dieting women, drinking water may promote weight loss by speeding up metabolism.
At the very least, it may cost you an extra trip (or two) to the bathroom, but it can’t hurt.
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