Water is an essential nutrient for all persons; thus, maintaining a chronic state of optimal hydration is recognized to provide health benefits. Fluid balance is maintained via thirst, a feedback-controlled variable, regulated acutely by central and peripheral mechanisms.
Water is the largest component of the human body and the total body water content varies from approximately 45 – 70% of the total body mass, corresponding to about 33 to 53 for 75 kg man. Although body water content varies greatly among individuals, the water content of the various tissues is maintained relatively constant.
For example, adipose tissue has low water content and lean tissue such as muscle and bone has a high water content, so the total fraction of water is the body is determine largely by the total fat content. In other words, a high fat content is related to a lower total water content as a percentage of body mass.
Water homeostasis is necessary to retain normal function of the body. Even small dysfunction in its distribution may cause reversible and later irreversible changes in cell and organ functions. The quality and proper distribution of water is a necessary condition to maintain health at different stages of life.
Daily water needs determined from fluid balance, water turnover, or consumption studies provide similar values for a given set of conditions. A daily water intake of 3.7 L for adult men and 2.7 L for adult women meets the needs of the vast majority of persons. However, strenuous physical exercise and heat stress can greatly increase daily water needs, and the individual variability between athletes can be substantial.
Water: The largest component of the human body
