Liquid H2O is the sine qua non of life. Making up
about 66 percent of the human body, water runs through the blood, inhabits the
cells, and
lurks in the spaces between. At every moment water escapes the body
through sweat, urination, defecation or exhaled breath, among other routes.
Replacing these lost stores is essential. When your water intake does not equal
your output, you can become dehydrated. Fluid losses are accentuated in warmer
climates, during strenuous exercise, in high altitudes, and in older adults,
whose sense of thirst may not be as sharp.
Here are some reasons why you should drink enough water or other
fluids every day:
1. Drinking Water Helps Maintain the Balance of Body Fluids.
The human body is composed of about 60% water. The functions of these fluids
include digestion, absorption, circulation, creation of saliva, transportation
of nutrients, and maintenance of body temperature.
"Through the posterior pituitary gland, your brain
communicates with your kidneys and tells it how much water to excrete as urine
or hold onto for reserves," says Guest, who is also an adjunct professor
of medicine at Stanford University. "Alcohol interferes with the brain and
kidney communication and causes excess excretion of fluids which can then lead
to dehydration," he added.
When you're low on fluids, the brain triggers the body's thirst
mechanism. And unless you are taking medications that make you thirsty, Guest
says, you should listen to those cues and get yourself a drink of water, juice,
milk, coffee -- anything but alcohol.
2. Water Can Help Control Calories. For years, dieters
have been drinking lots of water as a weight loss strategy. While water doesn't
have any magical effect on weight loss, substituting it for higher calorie
beverages can certainly help.
3. Water Helps Energize Muscles. Cells that don't maintain
their balance of fluids and electrolytes shrivel, which can result in muscle fatigue.
Drinking enough fluids is important when exercising.
4. Water Helps Keep Skin fresh. Your skin contains plenty
of water, and functions as a protective barrier to prevent excess fluid loss.
But don't expect over-hydration to erase wrinkles or fine lines, says Atlanta
dermatologist Kenneth Ellner, MD. "Dehydration makes your skin look more
dry and wrinkled, which can be improved with proper hydration," he says.
"But once you are adequately hydrated, the kidneys take over and excrete
excess fluids."
You can also help "lock" moisture into your skin by
using moisturizer, which creates a physical barrier to keep moisture in.
5. Water Helps Your Kidneys. Your kidneys do an amazing
job of cleansing and ridding your body of toxins as long as your intake of
fluids is adequate. When you're getting enough fluids, urine flows freely, is
light in color and free of odor. When your body is not getting enough fluids,
urine concentration, color, and odor increases because the kidneys trap extra
fluid for bodily functions.
If you chronically drink too little,
you may be at higher risk for kidney stones, especially in warm climates.
6. Water Helps Maintain Normal
Bowel Function. Adequate hydration keeps things flowing along your
gastrointestinal tract and prevents constipation. When you don't get enough
fluid, the colon pulls water from stools to maintain hydration -- and the
result is constipation.
"Adequate fluid and fiber is
the perfect combination, because the fluid pumps up the fiber and acts like a
broom to keep your bowel functioning properly," says Koelemay.
However there is a limit to it. Rehydration
can be overdone. There is such a thing as a fatal water overdose.
Earlier in 2007, a 28-year-old California woman died
after competing in a radio station's on-air water-drinking contest. After
downing some six liters of water in three hours in the "Hold Your Wee for
a Wii" (Nintendo game console) contest, Jennifer Strange vomited, went
home with a splitting headache, and died from so-called water intoxication.
In 2005 a fraternity hazing at California State University, Chico, left a 21-year-old man dead after he was forced to drink excessive amounts of water between rounds of push-ups in a cold basement. Club-goers taking MDMA ("ecstasy") have died after consuming copious amounts of water trying to rehydrate following long nights of dancing and sweating. Going overboard in attempts to rehydrate is also common among endurance athletes. A 2005 study in the New England Journal of Medicine found that close to one sixth of marathon runners develop some degree of hyponatremia, or dilution of the blood caused by drinking too much water.
Hyponatremia, a word cobbled together from Latin and Greek roots, translates as "insufficient salt in the blood." Quantitatively speaking, it means having a blood sodium concentration below 135 millimoles per liter, or approximately 0.4 ounces per gallon, the normal concentration lying somewhere between 135 and 145 millimoles per liter. Severe cases of hyponatremia can lead to water intoxication, an illness whose symptoms include headache, fatigue, nausea, vomiting, frequent urination and mental disorientation.
In humans the kidneys control the amount of water, salts and other solutes leaving the body by sieving blood through their millions of twisted tubules. When a person drinks too much water in a short period of time, the kidneys cannot flush it out fast enough and the blood becomes waterlogged. Drawn to regions where the concentration of salt and other dissolved substances is higher, excess water leaves the blood and ultimately enters the cells, which swell like balloons to accommodate it.
Most cells have room to stretch because they are embedded in flexible tissues such as fat and muscle, but this is not the case for neurons. Brain cells are tightly packaged inside a rigid boney cage, the skull, and they have to share this space with blood and cerebrospinal fluid, explains Wolfgang Liedtke, a clinical neuroscientist at Duke University Medical Center. "Inside the skull there is almost zero room to expand and swell," he says.
Thus, brain edema, or swelling, can be disastrous. "Rapid and severe hyponatremia causes entry of water into brain cells leading to brain swelling, which manifests as seizures, coma, respiratory arrest, brain stem herniation and death," explains M. Amin Arnaout, chief of nephrology at Massachusetts General Hospital and Harvard Medical School.
A few years ago Heinz Valtin, a kidney specialist from Dartmouth Medical School, decided to determine if the common advice to drink eight, eight-ounce glasses of water per day could hold up to scientific scrutiny. After scouring the peer-reviewed literature, Valtin concluded that no scientific studies support the "eight x eight" dictum (for healthy adults living in temperate climates and doing mild exercise). In fact, drinking this much or more "could be harmful, both in precipitating potentially dangerous hyponatremia and exposure to pollutants, and also in making many people feel guilty for not drinking enough," he wrote in his 2002 review for the American Journal of Physiology—Regulatory, Integrative and Comparative Physiology. And since he published his findings, Valtin says, "not a single scientific report published in a peer-reviewed publication has proven the contrary."
Most cases of water poisoning do not result from simply drinking too much water, says Joseph Verbalis, chairman of medicine at Georgetown University Medical Center. It is usually a combination of excessive fluid intake and increased secretion of vasopression (also called antidiuretic hormone), he explains. Produced by the hypothalamus and secreted into the bloodstream by the posterior pituitary gland, vasopressin instructs the kidneys to conserve water. Its secretion increases in periods of physical stress—during a marathon, for example—and may cause the body to conserve water even if a person is drinking excessive quantities.
Every hour, a healthy kidney at rest can excrete 800 to 1,000 milliliters, or 0.21 to 0.26 gallon, of water and therefore a person can drink water at a rate of 800 to 1,000 milliliters per hour without experiencing a net gain in water, Verbalis explains. If that same person is running a marathon, however, the stress of the situation will increase vasopressin levels, reducing the kidney's excretion capacity to as low as 100 milliliters per hour. Drinking 800 to 1,000 milliliters of water per hour under these conditions can potentially lead a net gain in water, even with considerable sweating, he says.
While exercising, "you should balance what you're drinking with what you're sweating," and that includes sports drinks, which can also cause hyponatremia when consumed in excess, Verbalis advises. "If you're sweating 500 milliliters per hour, that is what you should be drinking."
But measuring sweat output is not easy. How can a marathon runner, or any person, determine how much water to consume? As long as you are healthy and equipped with a thirst barometer unimpaired by old age or mind-altering drugs, follow Verbalis's advice, "drink to your thirst. It's the best indicator."
In 2005 a fraternity hazing at California State University, Chico, left a 21-year-old man dead after he was forced to drink excessive amounts of water between rounds of push-ups in a cold basement. Club-goers taking MDMA ("ecstasy") have died after consuming copious amounts of water trying to rehydrate following long nights of dancing and sweating. Going overboard in attempts to rehydrate is also common among endurance athletes. A 2005 study in the New England Journal of Medicine found that close to one sixth of marathon runners develop some degree of hyponatremia, or dilution of the blood caused by drinking too much water.
Hyponatremia, a word cobbled together from Latin and Greek roots, translates as "insufficient salt in the blood." Quantitatively speaking, it means having a blood sodium concentration below 135 millimoles per liter, or approximately 0.4 ounces per gallon, the normal concentration lying somewhere between 135 and 145 millimoles per liter. Severe cases of hyponatremia can lead to water intoxication, an illness whose symptoms include headache, fatigue, nausea, vomiting, frequent urination and mental disorientation.
In humans the kidneys control the amount of water, salts and other solutes leaving the body by sieving blood through their millions of twisted tubules. When a person drinks too much water in a short period of time, the kidneys cannot flush it out fast enough and the blood becomes waterlogged. Drawn to regions where the concentration of salt and other dissolved substances is higher, excess water leaves the blood and ultimately enters the cells, which swell like balloons to accommodate it.
Most cells have room to stretch because they are embedded in flexible tissues such as fat and muscle, but this is not the case for neurons. Brain cells are tightly packaged inside a rigid boney cage, the skull, and they have to share this space with blood and cerebrospinal fluid, explains Wolfgang Liedtke, a clinical neuroscientist at Duke University Medical Center. "Inside the skull there is almost zero room to expand and swell," he says.
Thus, brain edema, or swelling, can be disastrous. "Rapid and severe hyponatremia causes entry of water into brain cells leading to brain swelling, which manifests as seizures, coma, respiratory arrest, brain stem herniation and death," explains M. Amin Arnaout, chief of nephrology at Massachusetts General Hospital and Harvard Medical School.
A few years ago Heinz Valtin, a kidney specialist from Dartmouth Medical School, decided to determine if the common advice to drink eight, eight-ounce glasses of water per day could hold up to scientific scrutiny. After scouring the peer-reviewed literature, Valtin concluded that no scientific studies support the "eight x eight" dictum (for healthy adults living in temperate climates and doing mild exercise). In fact, drinking this much or more "could be harmful, both in precipitating potentially dangerous hyponatremia and exposure to pollutants, and also in making many people feel guilty for not drinking enough," he wrote in his 2002 review for the American Journal of Physiology—Regulatory, Integrative and Comparative Physiology. And since he published his findings, Valtin says, "not a single scientific report published in a peer-reviewed publication has proven the contrary."
Most cases of water poisoning do not result from simply drinking too much water, says Joseph Verbalis, chairman of medicine at Georgetown University Medical Center. It is usually a combination of excessive fluid intake and increased secretion of vasopression (also called antidiuretic hormone), he explains. Produced by the hypothalamus and secreted into the bloodstream by the posterior pituitary gland, vasopressin instructs the kidneys to conserve water. Its secretion increases in periods of physical stress—during a marathon, for example—and may cause the body to conserve water even if a person is drinking excessive quantities.
Every hour, a healthy kidney at rest can excrete 800 to 1,000 milliliters, or 0.21 to 0.26 gallon, of water and therefore a person can drink water at a rate of 800 to 1,000 milliliters per hour without experiencing a net gain in water, Verbalis explains. If that same person is running a marathon, however, the stress of the situation will increase vasopressin levels, reducing the kidney's excretion capacity to as low as 100 milliliters per hour. Drinking 800 to 1,000 milliliters of water per hour under these conditions can potentially lead a net gain in water, even with considerable sweating, he says.
While exercising, "you should balance what you're drinking with what you're sweating," and that includes sports drinks, which can also cause hyponatremia when consumed in excess, Verbalis advises. "If you're sweating 500 milliliters per hour, that is what you should be drinking."
But measuring sweat output is not easy. How can a marathon runner, or any person, determine how much water to consume? As long as you are healthy and equipped with a thirst barometer unimpaired by old age or mind-altering drugs, follow Verbalis's advice, "drink to your thirst. It's the best indicator."
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