Water
About Water
Water makes up about 60 percent of body weight in adults and is essential for life. It is the medium for chemical reactions, transports nutrients and wastes, lubricates joints, cushions tissues and regulates body temperature through sweating. Official adequate intake values for total water from beverages and food exist, and a meaningful share comes from food. The body regulates water balance through thirst, the hormone vasopressin from the posterior pituitary, and the renin angiotensin aldosterone system acting on the kidneys. Even mild dehydration can impair concentration, mood and physical performance. Drinking very large volumes without electrolytes can cause hyponatremia, a dangerous fall in blood sodium reported in endurance athletes and users of MDMA. Caffeinated beverages still contribute to hydration. Older adults have a blunted thirst response and are more prone to dehydration. The popular rule of eight glasses a day lacks a firm scientific basis, since needs vary with body size, activity, climate and diet.
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