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Water is the largest single component of an individual's body. Total body water (TBW) constitutes 60% of body weight in adult males and 50% in adult females. It decreases with age and is higher in athletes than in non athletes. Of the TBW, 38% is located intracellularly (referring to the inside of the cell) and 62% extracellularly (referring to outside the cell including blood plasma and lymph, saliva, fluids in the eyes, skin, tendons, muscles, skeleton, kidneys, etc.). Water is a vehicle for the transportation of nutrients, regulation of body temperature and participation in metabolic reactions. WATER BALANCE: INTAKE VERSUS OUTPUTThe maintenance of a constant normal volume of water in the body is essential to health. There is no provision for water storage in the body; therefore, the amount lost every 24 hours must be replaced to maintain health and efficiency. The sources of water intake and output are shown in the following diagram:
Water Intake
Water Output
Note: Water balance is directly related to the concentration levels of sodium and potassium. Excess sodium lowers potassium and causes water retention. Therefore, it is prudent to read labels on prepared food and not to over salt your meals. Keep in mind that restaurants usually use large amounts of salt to flavor food. WATER IN EXERCISE Exercise and sweating places demands on the body's fluid reserves and creates a relative state of dehydration. If sweating is excessive and fluids are not continually replaced, it severely compromises cardiovascular function & work capacity; it can also lead to a reduction in blood volume, sweat and core temperature which may rise to lethal levels. Exercise in hot and humid environments poses a great challenge to temperature regulation. In extreme conditions, fluid intake should be up to five or six times above normal. WATER AND THE KIDNEYS The main function of the kidney is to maintain a balance with respect to fluids, electrolytes (sodium, potassium and chloride) and various other molecules. A fixed amount of waste products from the normal breakdown of food is sent to the kidney and must be eliminated. Water intake of less than 0.5 liters makes it impossible for the kidney to eliminate all of the daily waste. The amount of water taken in affects the amount of urine in which waste products can be excreted. The output of urine form the kidney can range from a volume of as little as 0.5 liters to as much as 12 liters. Therefore, the more water ingested, the higher the volume of urine and the less concentrated it will be. HELPFUL TIPS
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