Fluids and Electrolytes
About 46% to 60% of the average adult’s weight is water, the primary body fluid. In good health this volume remains relatively constant and the person’s weight varies less than 0.2kg (0.5lb) in 24 hours, regardless of the amount of fluid ingested.
Water is vital to health and normal cellular function, serving as: (1) a medium for metabolic reactions within cells (2) a transporter for nutrients, waste products and other substances (3) a lubricant (4) an insulator and shock absorber (5)one means of regulating and maintaining body temperature.
- Age, sex, and body fat affect total body water
- Infants have the highest proportion of water, accounting for 70 to 80% of their body weight, but the proportion of body water decreases with aging
- In people older than 60 years old, it decreases to approximately 50%
- Fat tissue is essentially free of water, whereas lean tissue contain a significant amount of water
- Water makes up a greater percentage of a lean person’s body weight than an obese person
- Women, who have proportionately more body fat than men, have a lower percentage of body water