Water is essential to life and nutritional health. Humans can live for several weeks without food, but we can survive only a few days without water. Water makes up a large percentage of the body, in muscles, fat cells, blood and even bones.
Purpose
Every cell, tissue and organ requires water to function properly. Water transports nutrients and oxygen to the cells, provides a medium for chemical reactions to take place, helps to flush out waste products, aids in maintaining a constant body temperature, and keeps the tissues in the skin, mouth, eyes, and nose moist.
Precautions
The body does not store excess water, unlike it does with other nutrients. With physical exertion, water requirements increase; therefore, fluid replacement during exercise is critical. The longer the duration and the more physical exertion athletes put into their exercise, the more fluid they lose during workouts. To keep the body working at its best, it is essential to replenish lost fluid after workouts, and to stay well hydrated during exercise.
The body can accommodate extreme changes in water intake when the brain and kidneys are functioning normally. It is usually possible for a person to consume enough water to maintain blood volume and electrolyte balance in the blood. However, if a person is unable to consume enough water to equal excessive water loss, dehydration may result.
Water for sustaining life
The body works to maintain water balance through mechanisms such as the thirst sensation. When the body requires more water, the brain stimulates nerve centers in the brain to encourage a person to drink in order to replenish the water stores.
The kidneys are responsible for maintaining homeostasis of the body water (i.e. water balance) through the elimination of waste products and excess water. Water is primarily absorbed through the gastrointestinal tract and excreted by the kidneys as urine. Water intake can vary widely on a daily basis, influenced by such factors as: access to water, thirst, habit, and cultural factors. The variation in water volume ingested is dependent on the ability of kidneys to dilute and concentrate the urine as needed. There is a reservoir of water outside of the bloodstream that can replace or absorb excess water in the blood when necessary.
For a normal adult, a minimum daily intake between 700-800 ml (0.74-0.84 US quarts) is required to meet water losses and maintain the body's water balance. To protect against dehydration and developing kidney stones, greater water consumption (between 1.4-2 L/day or 1.5-2 US quarts/day) is advised. Water losses occur through evaporation in expired air and through the skin. Sweat losses are usually minimal but can be significant in warmer climates or with accompanying fever.
The following conditions increase water consumption needs. However, the amount of water necessary depends on body size, age, climate, and exertion level.
Water needs are increased by:
Exercise. Water is lost through perspiration.
Hot and humid climates.
High altitudes. The breathing rate is twice as fast as at sea level. At high altitudes, most water loss is due to respiration rather than perspiration.
Prescription drugs. If adequate water is not available for proper blood flow, medication can become concentrated in the bloodstream and become less effective.
Dieting. A reduced carbohydrate intake may have a diuretic effect because carbohydrates store water.
Airplane, bus, or train travel. The re-circulated air causes water to evaporate from skin faster.
Illness. Fever, diarrhea and vomiting lead to increased water losses.
Individuals should not wait until they are thirsty to replenish water stores. By the time the thirst mechanism signals the brain to encourage a person to drink water, already 1–3% of the body fluids are lost and an individual is mildly dehydrated.
Nutrition for optimal health
Not only is water necessary to sustain life, but proper nutrition is also required to ensure optimal health. Consumption of wide variety of foods, with adequate vitamin and mineral intake is the basis of a healthy diet. Vitamins are compounds that are essential in small amounts for proper body function and growth. Vitamins are either fat soluble: A, D, E, and K; or water soluble: vitamin B and C. The B vitamins include vitamins B1 (thiamine), B2 (riboflavin), and B6 (pyridoxine), pantothenic acid, niacin, biotin, folic acid (folate), and vitamin B12 (cobalamin).
Researchers state that no single nutrient is the key to good health, but that optimum nutrition is derived from eating a diverse diet including a variety of fruits and vegetables. Because there are many more nutrients available in foods such as fruits and vegetables than vitamin supplements, food is the best source for acquiring needed vitamins and minerals. The mineral nutrients are defined as all the inorganic elements or inorganic molecules that are required for life. As far as human nutrition is concerned, the inorganic nutrients include water, sodium, potassium, chloride, calcium, phosphate, sulfate, magnesium, iron, copper, zinc, manganese, iodine, selenium, and molybdenum. Other inorganic nutrients include phosphate, sulfate, and selenium. Inorganic nutrients have a great variety of functions in the body. The electrolytes are affected by fluid balance in particular (sodium, potassium, calcium, phosphate, and magnesium etc.). Water, sodium, and potassium deficiencies are most closely associated with abnormal nerve action and cardiac arrhythmias.
Laboratory studies with animals have revealed that severe deficiencies in any one of the inorganic nutrients can result in very specific symptoms, and finally in death, due to the failure of functions associated with that nutrient. In humans, deficiency in one nutrient may occur less often than deficiency in several nutrients. A patient suffering from malnutrition is deficient in a variety of nutrients.
Complications
Sodium deficiency (hyponatremia) and water imbalances (dehydration) are the most serious and widespread deficiencies in the world. These electrolyte deficiencies tend to arise from excessive losses from the body, such as during prolonged and severe diarrhea or vomiting. Diarrheal diseases are a major world health problem, and are responsible for about a quarter of the 10 million infant deaths that occur each year. Nearly all of these deaths occur in impoverished parts of Africa and Asia, where they result from contamination of the water supply by animal and human feces.
Dehydration is a deficit of body water that results when the output of water exceeds intake. Dehydration stimulates the thirst mechanism, instigating water consumption. Sweating and the output of urine both decrease. If water intake continues to fall short of water loss, dehydration worsens.
Dehydration induces water to move from the reservoir inside cells into the blood. If dehydration progresses, body tissues begin to dry out and the cells start to shrivel and malfunction. The most susceptible cells to dehydration are the brain cells. Mental confusion, one of the most common signs of severe dehydration may result, possibly leading to coma. Dehydration can occur when excessive water is lost with diseases such as diabetes mellitus, diabetes insipidus, and Addison's disease.
Dehydration is often accompanied by a deficiency of electrolytes, sodium and potassium in particular. Water does not move as rapidly from the reservoir inside of the cells into the blood when electrolyte concentration is decreased. Blood pressure can decline due to a lower volume of water circulating in the bloodstream. A drop in blood pressure can cause light-headedness, or a feeling of impending blackout, especially upon standing (orthostatic hypotension). Continued fluid and electrolyte imbalance may further reduce blood pressure, causing shock and damage to many internal organs including the brain, kidneys, and liver.
Consumption of plain water is usually sufficient for mild dehydration. However, when both water and electrolyte losses have occurred after vigorous exercise, electrolytes must be replaced, sodium and potassium in particular. Adding a little salt to drinking water or consuming drinks such as Gatorade during or following exercise can replace lost fluids. Individuals with heart or kidneys problems should consult a physician regarding the replacement of fluids after exercise.
Overhydration is an excess of body water that results when water intake exceeds output. Drinking large amounts of water does not typically lead to overhydration if the kidneys, heart, and pituitary gland are functioning properly. An adult would have to drink more than7.6 L per day (2 US gallons/day) to exceed the body's ability to excrete water. Excessive body water causes electrolytes in the blood, including sodium to become overly diluted. Overhydration occurs in individuals whose kidneys do not function normally, primarily in kidney, heart, or liver disease. People with these conditions may have to limit their water and dietary salt intake. Similar to dehydration, the brain is the most sensitive organ to overhydration. The brain cells can adapt to increased fluid volume when overhydration increases slowly, however, when it occurs rapidly, mental confusion, seizures, and coma can result.
Results
Consuming adequate food and fluid before, during, and after exercise can help maintain blood glucose during exercise and also maximize exercise performance. Athletes should be well-hydrated before exercise commencement and should drink enough fluid during and after exercise to maintain homeostasis. The same rules apply to non-athletes who are participating in physical activity or are in conditions that increase dehydration. Careful attention to water intake and urine output should provide the best results.
Avoiding some beverages such as coffee, tea, alcohol and caffeinated soft drinks may reduce the risk of dehydration. These beverages are all diuretics (substances that increase fluid loss). Water in foods, especially fruits and vegetables, is a great source of fluid. Fruits and vegetables can contain up to 95 percent water, so a well-balanced diet is a good way to stay hydrated.
KEY TERMS
Dehydration—A deficit of body water that results when the output of water exceeds intake.
Diuretic—An agent or drug that eliminates excessive water in the body by increasing the flow of urine.
Electrolyte—A substance such as an acid, bases, or salt. An electrolyte's water solution will conduct an electric current and ionizes. Acids, bases, and salts are electrolytes.
Homeostasis—An organism's regulation of body processes to maintain internal equilibrium in temperature and fluid content.
Overhydration—An excess of body water that results when water intake exceeds output.
Health care team roles
All health care professionals should recognize the importance of promoting proper nutrition and hydration. Encouraging patients to follow nutrition guidelines for adequate vitamin and mineral intakes is critical.
Patient education
Patients and individuals can be educated regarding the importance of hydration by nutrition experts and physicians as well as the need for good nutrition. Individuals themselves can become familiar with concepts for healthy eating using a number of resources such as the Food Pyramid, which provides a visual guide to healthy eating. In addition, the U.S. Department of Agriculture and the U.S. Department of Health and Human Services have developed official dietary guidelines that include ten basic recommendations for healthy eating:
Aim for a healthy weight.
Be physically active each day.
Let the Food Pyramid guide your food choices.
Choose a variety of grains daily, especially whole grains.
Choose a variety of fruits and vegetables daily.
Keep food safe to eat.
Choose a diet low in saturated fat and cholesterol, and moderate in total fat.
Choose beverages and foods to moderate intake of sugars.
Choose and prepare foods with less salt.
If you drink alcoholic beverages, do so in moderation.
BOOKS
Mindell, Earl and Hester Mundis. Earl Mindell's Vitamin Bible for the 21st Century. London: Warner Books, 1999.
Rodwell-Williams, Sue. Essentials of Nutrition and Diet Therapy (With CD-ROM for Windows and Macintosh). London: Mosby-Year Book, 1999.
Speakman, Elizabeth and Weldy, Norma Jean. Body Fluids and Electrolytes 8th ed. London: Mosby Incorporated, 2001.
Workman, M. Linda Introduction to Fluids, Electrolytes and Acid-Base Balance. London: W B Saunders Co., 2001.
PERIODICALS
Beck, L.H. "The aging kidney. Defending a delicate balance of fluid and electrolytes." Geriatrics 55, no. 4 (2000): 26-28, 31-32.
Sawka, M.N. and Montain, S.J. "Fluid and electrolyte supplementation for exercise heat stress." American Journal of Clinical Nutrition 72, no. 2 Suppl. (2000): 564S-572S.
ORGANIZATIONS
American Dietetic Association. 216 W. Jackson Blvd. Chicago, IL 60606-6995. (312) 899-0040. <http://www.eatright.org/>.
Food and Nutrition Information Center Agricultural Research Service, USDA. National Agricultural Library, Room 304, 10301 Baltimore Avenue, Beltsville, MD 20705-2351. (301) 504-5719. Fax: (301) 504-6409. <http://www.nal.usda.gov/fnic/>. fnic@nal.usda.gov.
OTHER
Food and Nutrition Professionals Network. <http://nutrition.cos.com/>.
Nr-Space, et al. Fluids & Electrolytes CD-ROM. Delmar Publishers, 2001.
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