Water is necessary for life; without it, you can survive only a few days. Water makes up 40 to 70 percent of a human's body weight depending on age, gender and body composition. Water constitutes 60 percent of muscles, 95 percent of the brain, 82 percent of blood and 90 percent of the lungs. Drinking enough water each day is important in maintaining physiological processes, regulating temperature, preventing disease and preventing dehydration.
Physiological Processes
Water makes up the fluid that surrounds cells, and normal cellular function is based on a balance of intracellular, interstitial and extracellular fluid. Water is necessary for metabolic reactions by serving as the solvent for minerals, vitamins, amino acids, glucose and many other molecules. It also carries nutrients and waste products throughout the body and serves as the fluid that lubricates and cushions the joints and many organs.
Regulating Temperature
Water aids in the regulation of normal body temperature through perspiration. Evaporation is the main defense against overheating and is the body's cooling mechanism. The evaporation of sweat from the skin removes excess heat from the body and cools the blood diverted from interior tissues to the surface.
Preventing Disease
In the book "Understanding Nutrition," Ellie Whitney and Sharon Rady Rolfes write that drinking plenty of water protects the colon and bladder against cancer by removing waste products from the body and diluting urine. Adequate water intake also reduces the risk of kidney stones, prostate cancer and breast cancer.
Dehydration
Dehydration occurs with just a 1 to 2 percent decrease in the body's water supply. Some early signs of dehydration include thirst, fatigue and weakness. Later stages of dehydration include flushed skin, headaches, dizziness, increased respiratory rate and exhaustion. End stages of dehydration consist of loss of balance, spastic muscles, delirium and collapse.
Adequate Water Intake
Authors Whitney and Rolfes make water recommendations based on diet, activity, environmental temperature and humidity. A general guideline is 1 to 1.5 mL/kcal expended in adults and 1.5 mL/kcal expended in infants and athletes. For example, a person who expends 2,000 calories a day would be required to drink 2 to 3 liters of water, or approximately eight to 12 cups.
References
- "Exercise Physiology: Energy, Nutrition, and Human Performance"; W.D. McArdle, F.I. Katch, V.L. Katch; 2001
- "Understanding Nutrition"; E. Whitney, S.R. Rolfes; 2005
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