Water and Nutrition Health Article

Definition

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.