Why are fluids important?
Fluids, especially water, serve as the medium for a cell’s biochemical reactions and facilitates a constant internal temperature. Water comprises about 55 to 65% of the entire body mass and 80% to 84% of kidney, lung, and skeletal muscle tissues. Water must be consumed by humans because:
The Science of Urine Color
Attempting to simplify the analysis of urine, Professor Armstrong oversaw a series of experiments, beginning in 1994, testing the validity of a numbered urine color chart. The logic underlying the first study (1) proposed that virtually anyone could determine her/his hydration state, if urine color were directly proportional to the gain or loss of body water. The initial laboratory study involved developing a numbered scale of colors ranging from very pale yellow (number 1) to brownish green (number 8). This research demonstrated that urine color likely would be useful and effective during daily activities, exercise, and heavy labor.
A few years later, a second investigation (2) evaluated the effects of a large water loss (4% of body weight) on urine biomarkers. Nine subjects performed strenuous exercise in a 98°F laboratory environment, then undertook a 21-hour period of oral rehydration. Interestingly, urine color tracked dehydration as effectively as urine speciﬁc gravity, urine osmolality, plasma osmolality, plasma total protein concentration, or plasma sodium concentration.
A third investigation (3) observed hydration biomarkers of women, as they undertook 6 weeks of physical training in a hot laboratory environment. Again, urine color proved to be strongly related (i.e., as determined by statistical correlation) to hydration state. When urine color was pale yellow or straw colored, these women were well hydrated. The above research does not mean, however, that urine (or any body fluid) offers a perfect index of hydration, every hour of the day. No body fluid (urine, blood, saliva) perfectly reveals hydration status perfectly in all situations (4), because the brain responds each day to many dynamic challenges to water balance.
Take Away for You
The above investigations, research conducted in California among elderly adults (5, 6,7), and a published review of 12 potential hydration biomarkers (4), show that urine color provides a simple and valid method to monitor hydration in real time, during the course of daily activities or physical exercise. Urine color is not a substitute for sophisticated laboratory techniques, in hospitals or laboratories, but it offers anyone an opportunity to check their own body water balance, at any time of the day.
Click on the titles below to download the scientific papers: