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Water intoxication (also known as hyperhydration or water poisoning) is a potentially fatal medical condition in which an individual's intake of water exceeds a safe amount. This is attributed to various causes, especially as osmotic pressure, which affects passive transport in the body, is upset.
Physiology of water intoxication
Drinking excess water in the absence of dietary sodium results in hyponatremia, an overdilution of sodium in the blood plasma, which in turn causes an osmotic shift of water from the blood plasma into brain cells. The brain cells swell as result of osmotic pressure, and will ultimately cease to function. Also, many other cells in the body may undergo cytolysis, where the cell membranes unable to stand the osmotic pressure explode, killing the cell. Initial symptoms typically include light-headedness, sometimes accompanied by nausea, vomiting, headache and/or malaise. Plasma sodium levels below 100 mmol/L (2.3g/L) frequently result in cerebral edema, seizures, coma, and death within a few hours of drinking the excess water. As with an alcohol overdose, the progression from mild to severe symptoms may occur rapidly as the body continues to absorb water from the stomach.
A person with two healthy kidneys can rid themselves of about 1.5 litres of water per hour at maximum filtration (other studies find the limit to be as little as 0.9L/hr ) . Consuming as little as 1.8 liters of water in a single sitting may prove fatal for a person adhering to a low-sodium diet, or 3 liters for a person on a normal diet.
Persons at high risk of water intoxication
Certain activities and conditions put a person at elevated risk of water intoxication.
Marathon runners are susceptible to water intoxication if they drink only water while running. Sweating profusely, their sodium levels drop while they consume large amounts of fluids to quench their thirst. This puts them at high risk for water intoxication and thus medical personnel are trained to immediately suspect water intoxication when runners collapse or show signs of confusion. Properly designed sports drinks include electrolytes to prevent water intoxication.
A frequent side-effect of diabetes is polydipsia, an increased sense of thirst. The thirst is not a result of insufficient water in the blood but rather a disruption of the thirst regulatory mechanism. Thus diabetics are at risk for water intoxication.
Many cases of water intoxication are related to drug use, in particular the drug MDMA (commonly referred to as ecstasy); while the media reports this as an overdose it may in fact be an idiosyncratic reaction (perhaps an unintended consequence of harm reduction advice to drink plenty of water when raving), exacerbated by hyperthermia.
Although water intoxication includes hyponatremia, the two conditions are in fact distinct. Hyponatremia may occur in the absence of elevated water intake; for instance in conditions such as diarrhea where sodium is flushed excessively from the body and the person does not drink anything.
Psychogenic polydipsia is the psychiatric condition in which patients feel compelled to drink large quantities of water. The condition is often a single symptom in a broader syndrome of psychiatric indications. Patients suffering from psychogenic polydipsia are at high risk of water intoxication, especially as the initial symptoms of lightheadedness and confusion may be misdiagnosed by care-takers as due to other causes.
Famous cases of water intoxication
In a much-publicized case of fraternity hazing, four members of the Chi Tau House at California State University, Chico pled guilty to forcing 21-year-old student Matthew Carrington to drink excessive amounts of water while performing calisthenics in a frigid basement as part of initiation rites on the 2nd of February 2005. He collapsed and died of heart failure due to water intoxication.
Other fatalities due to water intoxication include Leah Betts , Anna Wood , 2002 Boston Marathon competitor Cynthia Lucero  and Washington, D.C. police officer James McBride . New Zealand race-walker Craig Barrett collapsed during the last kilometer of the 50km walk in the 1998 Commonwealth Games in a non-fatal case of water intoxication.
Prevention of water intoxication
The best way to prevent water intoxication is to drink liquids in moderation and to ensure the daily diet includes sufficient electrolytes (specifically salt). Sports drinks are popular among athletes because they provide the necessary electrolytes to support extended exercise. They help keep the body balanced and carrying the right amount of fluids. However, for those who don't like or want sports drinks, the recommended amount of sodium intake based on a 2,000 calorie diet is 2.5 grams every 24 hours.
Note that a person's innate sense of thirst will not warn of an impending case of water intoxication. This is because while the human thirst mechanism accurately detects the level of water in the blood, the human salt craving mechanism does not respond to an acute drop in blood sodium level, so the person does not realize he or she needs sodium immediately.
ca:Hiperhidratació de:Hyperhydration es:Hiperhidratación he:הרעלת מים
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