Hyponatremia

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Members may find the following to be of interest:

Strange but True: Drinking Too Much Water Can Kill

http://www.sciam.com/article.cfm?chanID=sa029 & articleID=4EC337D6-E7F2-

99DF-3549D1F6684BC11A

June 21, 2007

In a hydration-obsessed culture, people can and do drink themselves

to death.

By Coco Ballantyne

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 but rehydration can

be overdone. There is such a thing as a fatal water overdose.

Earlier this year, 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, Strange vomited,

went home with a splitting headache, and died from so-called water

intoxication.

There are many other tragic examples of death by water. 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.

Where did people get the idea that guzzling enormous quantities of

water is healthful? 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 ph Verbalis, chairman of medicine at town

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. "

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Carruthers

Wakefield, UK