Water intoxication

Overview
Water intoxication (also known as 'hyperhydration' or water poisoning) is a potentially fatal disturbance in brain function that results when the normal balance of electrolytes in the body is pushed outside of safe limits by a very rapid intake of water. Normal, healthy (both physically and nutritionally) individuals have little to worry about accidentally overconsuming water. Nearly all deaths related to water intoxication in normal individuals have resulted either from water drinking contests, in which individuals attempt to consume several gallons over the course of just a few minutes, or long bouts of intensive exercise during which time electrolytes are not properly replenished, yet massive amounts of fluid are still consumed.

Physiology
Blood contains electrolytes (particularly sodium compounds, such as sodium chloride) in concentrations that must be held within very narrow limits. Water enters the body orally or intravenously and leaves the body primarily in urine, sweat, and exhaled water vapor. If water enters the body more quickly than it can be removed, body fluids are diluted and a potentially dangerous shift in electrolyte balance occurs. In other words, the body has too much water and not enough electrolytes.

Most water intoxication is caused by hyponatremia, an overdilution of sodium in the blood plasma, which in turn causes an osmotic shift of water from extracellular fluid (outside of cells) to intracellular fluid (within cells). The cells swell as a result of changes in osmotic pressure and may cease to function. When this occurs in the cells of the central nervous system and brain, water intoxication is the result. Additionally, many other cells in the body may undergo cytolysis, wherein cell membranes that are unable to stand abnormal osmotic pressures rupture, killing the cells. Initial symptoms typically include light-headedness, sometimes accompanied by nausea, vomiting, headache and/or malaise. Plasma 19 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 alcohol poisoning, the progression from mild to severe symptoms may occur rapidly as the water continues to enter the body from the intestines or intravenously.

A person with healthy kidneys can excrete about 900ml (0.24 gal)/hr. However, this must be modulated by potential water losses via other routes. For example, a person who is perspiring heavily may lose 1 L/hr (0.26 gal) of water through perspiration alone, thereby raising the amount of water that must be consumed before the individual crosses the threshold for water intoxication. The problem is further complicated by the amount of electrolytes lost in urine or sweat, which is variable within a range controlled by the body's regulatory mechanisms.

Water intoxication can be prevented by consuming water that is isotonic with water losses, but the exact concentration of electrolytes required is difficult to determine and fluctuates over time, and the greater the time period involved, the smaller the disparity that may suffice to produce electrolyte imbalance and water intoxication.

Sodium is not the only mineral that can become overdiluted from excessive water intake. Magnesium is also excreted in urine. According to the National Institutes of Health, "magnesium deficiency can cause metabolic changes that may contribute to heart attacks and strokes." Intravenous magnesium is used in cardiac care units for cardiac arrhythmias.

Low body mass (infants)
It can be very easy for children under a year old to absorb too much water – especially if the child is under nine months old, because with their small body mass, it is easy to take in a large amount of water relative to body mass. It is also possible for a child to absorb too much water if submerged in it.

Endurance sports
Marathon runners are susceptible to water intoxication if they drink only water while running. Although sweat is relatively hypotonic compared with body fluids, marathon runners perspire heavily for long periods, potentially causing their sodium levels to drop when they consume large amounts of fluids to quench their thirst. The replacement fluids may not contain sufficient sodium to replace what has been lost, and this puts them at high risk for water intoxication. Medical personnel at marathon events are trained to immediately suspect water intoxication when runners collapse or show signs of confusion. Properly designed electrolyte-replacement drinks and some sports drinks include electrolytes that make them roughly isotonic with sweat, which helps to prevent water intoxication.

Note that overconsumption of sodium (in drinks or also in food), as well as inadequate intake of water, can cause hypernatremia, a disorder that is nearly the opposite of water intoxication and equally dangerous. Improper use of salt tablets can cause hypernatremia also.

Overexertion and heat stress
Any activity or situation that promotes heavy sweating can lead to water intoxication when water is consumed to replace lost fluids. Persons working in extreme heat and/or humidity for long periods must take care to drink and eat in ways that help to maintain electrolyte balance. Persons using drugs such as MDMA ("Ecstasy") may overexert themselves, perspire heavily, and then drink large amounts of water to rehydrate, leading to electrolyte imbalance and water intoxication (See the case of Leah Betts). Even people who are resting quietly in extreme heat or humidity may run the risk of water intoxication if they drink large amounts of water over short periods for rehydration.

Psychiatric conditions
Psychogenic polydipsia is the psychiatric condition in which patients feel compelled to drink large quantities of water, thus putting them at risk of water intoxication. This condition can be especially dangerous if the patient also exhibits other psychiatric indications (as is often the case), as his or her care-takers might misinterpret the hyponatraemic symptoms.

Specific disease
Diarrhea and vomiting can result in very large electrolyte losses, and although drinking water will replace lost water, the lost electrolytes may not be adequately replaced, which can result in water intoxication. Replacement fluids for vomiting and diarrhea should be properly balanced to make them isotonic with the fluids lost in these conditions. Special formulations exist for oral rehydration therapy in these cases.

A great many disorders can affect electrolyte balance, especially disorders of the kidneys. Diuretic therapy, mineralocorticoid deficiency, osmotic diuresis (as in the hyperglycemia of uncontrolled diabetes), and the multiple disorders associated with AIDS are other common causes of electrolyte imbalance, although they do not always produce water intoxication.

Iatrogenic
When an unconscious person is being fed intravenously (for example, total parenteral nutrition or via a nasogastric tube) the fluids given must be carefully balanced in composition to match fluids and electrolytes lost. These fluids are typically hypertonic, and so water is often co-administered. If the electrolytes are not monitored (even in an ambulatory patient) either hypernatremia or hyponatremia may result.

Some neurologic/psychiatric medications (Trileptal, among others) have been found to cause hyponatremia in some patients. Patients with diabetes insipidus are particularly vulnerable due to rapid fluid processing.

Treatment
Mild intoxication may remain asymptomatic and require only fluid restriction. In more severe cases, treatment consists of:
 * Diuretics to increase urination, which are most effective for excess blood volume
 * Saline given intravenously to restore sodium electrolyte levels
 * Vasopressin receptor antagonists

Prevention
Water intoxication can be prevented if a person's intake of water and electrolytes closely matches his or her losses. The body's regulatory mechanisms provide a very generous margin of safety if the two are imbalanced, but some extreme activities (such as heavy, prolonged physical exertion), as well as disease states, can overwhelm or impair these mechanisms. Avoid situations that provoke extreme or prolonged perspiration. Drinking fluids that are specially balanced to replace lost electrolytes can also help to prevent intoxication. Eating regularly can provide needed electrolytes if only normal water is available for rehydration.

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, not all drinks advertised as sports drinks are suitable for this purpose, and professional advice should be sought for potentially risky situations such as those described above.

Note that a person's innate sense of thirst is more sensitive to overall dehydration than to changes in electrolytes. Thus, it is possible to develop water intoxication while trying to satisfy thirst, if one drinks a great deal of water over a short period. A dangerous drop in electrolytes, such as the hyponatremia that leads to water intoxication, will not have any effect on thirst if one is sufficiently dehydrated.

For people suffering from dehydration due to the heavy perspiration associated with heavy exertion or heat stress, drinking water to rehydrate is much more important than avoiding water intoxication, since the former is extremely common and the latter is rare. One should never avoid drinking water under such conditions; instead, other steps should be taken to ensure that electrolytes are replaced as well, as noted above.

Notable cases

 * On January 12, 2007, Jennifer Strange, a 28-year-old woman and a mother of 3, from Rancho Cordova, California, was found dead in her home by her mother hours after trying to win one of Nintendo's Wii game consoles in KDND 107.9 "The End" radio station's "Hold Your Wee for a Wii" contest, which involved drinking large quantities of water without urinating. However, no criminal charges were pressed. The Federal Communications Commission has launched its own investigation to determine if the station violated the terms of its operating license.
 * Leah Betts died on the 16th of November 1995 after taking an ecstasy tablet at her 18th birthday party and subsequently drinking too much water; the case received mass media coverage throughout the United Kingdom.
 * In a much-publicized case of fraternity hazing, four members of the Chi Tau (formerly Delta Sigma Phi) House at California State University, Chico pleaded 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 February 2, 2005. He collapsed and died of heart failure due to water intoxication.
 * On September 12, 1999, US Air Force basic trainee Michael J. Schindler died of heat stroke, severely complicated by water intoxication, two days after becoming seriously ill during a 5.8 mile march. The Air Force changed its recruit training procedures as a result.
 * New Zealand race-walker Craig Barrett collapsed during the last kilometer of the 50 km walk in the 1998 Commonwealth Games in a non-fatal case of water intoxication.
 * Other notable fatalities due to water intoxication include Andy Warhol, Anna Wood, 2002 Boston Marathon competitor Cynthia Lucero, and Washington, D.C. police officer James McBride.