The summer months often bring bad news: poolside accidents, amusement park mishaps, and hyponatraemic encephalopathy. What? Yes, drinking too much water can cause a serious condition characterized by a lack of salt in the blood, leading to water imbalance and water build-up in the brain. Hyponatraemia actually means low (hypo) sodium (natr) levels in the body. Most recently, a female marathon runner in a 2002 Boston race died because she ingested excessive amounts of a sports drink before and during the race. Ask anybody how much water a human being should consume in one day and you will hear answers varying from eight to twelve cups per day for the typical layman, and higher numbers from exercise enthusiasts and military personnel. This is often more water than your body needs. Consuming excess water can be detrimental, even fatal.
|Search the USDA nutrient database to find out the percentage of water in foods, at: http://
Water is essential for many chemical reactions in the body and is needed for bodily excretions. It also helps regulate body temperature, transports water-soluble vitamins, and gives tissues their structure. In fact, the body is about 60% water, and many of our organs are mostly water. However, water requirements vary according to environment, exercise, medications, kidney health, and food intake. Drink too much and the benefits may be outweighed by the diluting of salts within your body. While drinking eight cups may not do any harm, it is unnecessary for most people and can put an increased strain on the kidneys if done too quickly. Drinking significantly greater amounts, such as twenty cups a day, under the assumption "if some is good, more is better," can be dangerous.
The symptoms of hyponatraemic encephalopathy are similar to those of dehydration, including nausea, vomiting, and confusion. Therefore, people with symptoms may think that they need to drink still more, but further water consumption can lead to seizures, delirium, coma and death.
The accuracy of water requirement statements is remarkably unclear, and the original basis for the suggestion of eight cups per day was not based on scientific evidence. Dr. H. Valtin from Dartmouth Medical School conducted a review to find the origin of this advice but to no avail. The extensive review failed to bring to light any scientific studies in support of eight cups a day. In contrast, he found surveys published in peer reviewed journals suggesting that large amounts of water are in fact, unnecessary. He does emphasize that this conclusion holds true for healthy sedentary adults, while rigorous activity calls for increased water consumption.
Dr. Ruth Kava, our Director of Nutrition here at the American Council on Science and Health, thinks that the origin of "eight cups a day" may be a misinterpretation of statements in physiology textbooks about total bodily fluid requirements being eight cups per day. This "fluid" however, can come from food, drink, and metabolism byproducts, not necessarily from drinking eight cups of water.
The eight cups dictum typically leaves foods out of the equation and focuses on drinking actual cups of water. Foods contribute a substantial amount of water to the diet, as 90% of the weight of some fruits and vegetables is accounted for by water. Water is found in some surprising places. Yogurt, salmon, eggs, and potatoes are about 75% water, and four ounces of broiled salmon provides about one half cup of water.
People don't always count soups, coffee, and tea in their daily tally either, though all contribute to water intake. Although caffeine has a mild diuretic effect, the water in coffee and tea can still add to the total intake, especially amongst regular caffeine drinkers who are not affected as much by caffeine. Eating according to dietary guidelines and including five fruits and vegetables daily will add up to about four to six cups of water (also see http://www.acsh.org/publications/priorities/1302/water.html). Your metabolism also produces about one cup of water. Add to that beverages consumed throughout the day and the total easily rises past eight.
Children and adults alike, who are trying to eat according to guidelines, may count grams of calories, fat, and carbohydrates and strive to drink all eight (literal) cups. Focusing on such guidelines, it is easy to lose sight of personal dictates for thirst and obeying your own thirst is the current best advice regarding water consumption, especially for athletes.
Recent Cases of Excess
Hyponatraemic ecephalopathy can result when too much water is ingested too quickly and the brain swells due to a sodium imbalance. This is most common amongst athletes, military personnel and the elderly. There were 125 Army hospitalizations for hypontraemia between 1989 and 1996. These cases were associated with excessive water drinking and were often mistaken for dehydration and patients were unfortunately given additional water.
In July1995, there were nine cases in one day. Due to heat exhaustion, Marine Corps recruits drank ten to twenty-two quarts of water in a short time period. Five of them developed seizure activity and progressed to delirium and/or coma. After treatment, most returned to full duty.
In July 1997, there were four cases of hyponatraemia reported at Fort Benning, GA and four more cases from other recruit training centers. Out of these, there was one fatal case: a healthy eighteen-year-old drank three quarts of water prior to arriving at a rifle range. He drank five more quarts before 11am and began to feel dizzy. He therefore rested and drank two more quarts and waited to see an improvement. When his symptoms did not improve he drank ten more quarts over the next two hours. He became increasingly confused and lethargic and lost consciousness. He later died.
Athletes and military personnel are often taught to drink beyond their bodies' requirements in order to prevent dehydration. Military personnel used to be taught to drink two quarts per hour when exercising in a hot environment. This advice is not based on scientific evidence, and it fails to take into account that humans carry a reserve of some two liters of water. It is now thought people should follow the dictates of thirst and not to exceed 1-1.5 quarts per hour.
Older people are often advised to drink much more water than they can handle because the thirst sensation is less accurate as the aging process progresses. However, high fluid intake can cause them to lose sleep, as they will need to use the bathroom during the night and can also worsen congestive heart failure. Many older patients may already be at risk of hyponatremia because their kidneys reabsorb too much water.
What does all this information mean for ordinary people? Do not stop drinking water. Our bodies do need it, especially in the hot summer months when we perspire more. But if you find that eight cups of water sends you to the bathroom frequently, by all means drink less. There is no need to have a universal requirement, since everybody has different water needs. We don't have a universal calorie requirement and the same should hold true for water.