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H2O Down-Low: Did you know your body absorbs cold water faster than warm, and that you might not need those eight glasses a day? |
Comments (1)Six Myths That Don't Hold Water
By Linda LindsayPublished: August 15, 2010
Practical Wellness
No one would argue that we shouldn’t drink lots of water. Our bodies, after all, are almost 75 percent H2O.
But how much do you need for optimal health? Popular advice says you must drink eight glasses a day to avoid fatigue and memory problems, shun caffeinated drinks to avoid dehydration, and drink room-temperature water so your body can absorb it easily. You should sip water constantly, because if you feel the slightest twinge of thirst, you’re already dehydrated. Right?
Actually, not one of these bits of wisdom is backed by research. Here’s a look at the origins — and truths — behind six popular water myths.
Myth #1: You need to drink eight 8-ounce glasses of water each day. In 2002, The American Journal of Physiology published a paper exploring the origins and scientific evidence for this popular myth, known as “8 x 8” for short. The author discovered that no one — not researchers, doctors, nutritionists, or dieticians — knew where 8 x 8 originated, although everyone could readily spout the advice.
Computing our daily water needs shouldn’t be rocket science, so can’t we just do the math? If the average adult loses eight to 10 cups of water a day to breathing, sweating, and trips to the bathroom, but takes in about four cups of water a day in the food they eat, that leaves four to six cups that need to be replenished by drinking.
The problem with these averages is, well, they’re averages. In the real world, everyone’s individual physiology, diet, activity level, body size, and the climate in which they live will influence their actual needs, which may be less — or much more — than eight glasses a day.
If left to our own devices, how much would we drink? Research on more than 15,000 Americans shows that adults typically drink eight or more cups of fluid a day. However, half of those fluids consist of coffee, tea, milk, juice, and alcoholic beverages.
Should those count toward your daily intake? Some studies say yes (see sidebar), but proponents of 8 x 8 typically say no… which brings us to Myth #2.
Myth #2: Caffeinated drinks cause dehydration. Despite hundreds of websites run by doctors, nutritionists, and alternative health practitioners telling you that caffeine causes dehydration, the notion is completely false.
The University of Nebraska tested healthy adults after the subjects drank various combinations of water, coffee, citrus soda, and caffeinated regular and diet cola. Turns out it didn’t matter what the subjects drank; even when 75 percent of their fluids were caffeinated, the subjects stayed as hydrated as when they drank only water. Other research on hard-core cyclists found similar results. Even the American College of Sports Medicine states that caffeine does not cause dehydration.
This myth probably arose because caffeine is a diuretic and makes you visit the bathroom more frequently, leading people to believe they’re losing more fluids than they’re taking in. They’re not.
Myth #3: By the time you’re thirsty, you’re already dehydrated. It’s true that by the time you register thirst, your body has already taken measures to conserve water; namely, you’ve released vasopressin, a hormone that signals your kidneys to concentrate urine and allow resorption of water back into the bloodstream. But does this mean you’re dehydrated? Hardly, say physiologists.
Thirst sets in well before actual dehydration, which is defined as losing three percent or more of your body weight in water (for a 130-pound person, this is four pounds of water loss; for a 200-pound person, six pounds).
As one physiologist put it, “The body’s [complex water-regulating system] and thirst are so sensitive, quick and accurate, that it is hard to imagine that evolutionary development left us with a chronic water deficit that has to be compensated by forcing fluid intake.” And indeed, Penn State researchers found that when people are left to their own devices, they’re actually very good at staying hydrated.
Myth #4: Warm water gets absorbed faster because it’s closer to body temperature. Amazingly, cold water actually passes through the stomach faster than warm water, allowing it to reach the intestines and be absorbed more quickly into the bloodstream. However, even if you’re in a hurry to hydrate, such as during or after an athletic event, there’s no need to chug water so cold that you suffer an ice cream headache. The American College of Sports Medicine recommends that fluids be cool, between 59 and 72 degrees.
Myth #5: Drinking lots of water causes weight loss. Ah, if only this were true. Unfortunately, water doesn’t trigger the body’s satiety, or “fullness,” signal, so it won’t stave off hunger. But there are ways in which water can help you lose weight. The most obvious is to substitute water (or unsweetened tea) for caloric drinks like soda, lattes, and juice.
The second is to incorporate water into your food. In one surprising study, women who ate chicken soup felt fuller than those who ate chicken casserole along with a glass of water, even though the two meals contained identical ingredients and calories. What’s more, the soup eaters ate fewer calories at their next meal.
Myth #6: You can never drink too much water. It’s hard to believe that water could ever be harmful, but people have actually died from drinking too much — a condition called water intoxication, or hyponatremia.
People who succumb to water intoxication fall into two categories: those who have a medical condition or are taking antidiuretic drugs; and those who are otherwise healthy, but have forced copious amounts of water without also taking in electrolytes — a situation that causes the body’s sodium to drop to lethal levels.
Endurance athletes are most at danger, but hyponatremia deaths have occurred during fraternity hazing rituals, water-drinking contests, and in people on Ecstasy (the drug causes extreme thirst but interferes with the ability to urinate excess water).
Athletes need to listen to their bodies and replace electrolytes with Gatorade-type drinks. Strangely, the early symptoms of hyponatremia (muscle cramps, disorientation, and nausea,) mimic dehydration, often causing athletes to drink more water.
The Bottom Line
Drink when you’re thirsty, drink more when it’s hot or you’re working out, and go ahead and sip from that water bottle as frequently as you wish — it sure won’t hurt, and it may cut your risk of a number of diseases.
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