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Evaluating Dehydration
Thirst is how most people remember to drink water. But this is not the best way to stay hydrated, since the brain’s thirst center does not send a message until you are almost 2 percent dehydrated. By then, you already have lost function associated with dehydration. The kidneys, however, respond to dehydration much sooner than the brain tells you you’re thirsty. If your urine output is diminished, it may be one of the first indications that you’re beginning to dehydrate. What is meant by diminished? This, of course, varies with the individual. If you’re not urinating at least six to eight times each day, for example, or if each time you urinate the volume is noticeably reduced, you may be dehydrated.
While the best measurement of dehydration involves blood tests such as isotope techniques and plasma osmolality, most health-care professionals and athletes can rely on other practical evaluations. These include urine-specific gravity and urine osmolality. Even more practical, and quite accurate, is the color of urine.
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All athletes can learn to evaluate the color of their urine regularly. It maybe the best and earliest indicator that you need more water. Pale or light yellow color or clear urine usually indicates good hydration status. But if urine color is brighter yellow or a darker brown/tan color, this it may indicate dehydration. The exception is for the first urine in the morning, which is darker because you’re mildly dehydrated due to no (or reduced) water intake during the night. (This is the reason drinking water should be one of the first things you do upon awakening.)
Synthetic vitamin B2 (riboflavin) typically produces a very bright yellow color of the urine within hours of taking it. This chemical typically comes from a vitamin supplement.