Tsz Wing Ho
PHYS 1
Mon & Wed 2-5pm
March 19, 2012
Urine Volume Decreases with Sodium Intake
Abstract
As the kidneys serve many important roles in maintaining homeostasis in our body, they
help not only remove metabolic waste products, but they also regulate water and electrolyte
balances in our body (Bettinelii, 2009). For maintenance of homeostasis, it is vitally important
for the kidneys to adjust their excretion rates to match the intakes of various substances. For
instance, researchers support that people who drink Gatorade sport drinks help conserve water
retention in the body, resulting in a decrease in urine volume. They explain that since Gatorade
contains many different electrolytes such as sodium and potassium, they are the important ions
that help regulate the extra-cellular fluids in our body. To study whether drinking Gatorade helps
prevent water losses in the body, this experiment compares the urine volume between the waterin takers (the controlled group) and the Gatorade drinkers (the experimental group). The urine
sample of each group is collected in every 30 minutes for a period of 120 minutes. Results
support that for the Gatorade drinkers, their urine volume is gradually decreasing in every 30
minutes, whereas the urine volume of the water drinkers is gradually increasing in every 30
minutes. Nevertheless, more investigations are still required to be more confirmed with the
hypothesis, since the quantity of urine formed can also be affected by other factors, such as
dietary intake, individual's health condition and metabolism (Coyle, 2003).
Introduction
Undoubtedly, we lose water routinely when we are breathing, sweating, and eliminating
wastes by urination. However, an excessive loss of body fluid may lead to dehydration and
impair physiological functions and performances in the body (Coyle, 2003). Dehydration occurs
when the amount of water leaving the body is greater than the amount being taken in. (Bettinelli,
2009). It has been said that people should drink a significant amount of water in order to
replenish water losses from sweating during exercise. However, a recent article reveals that
drinking only pure water is not the safest choice for those who participate in any strenuous or
long-duration exercise. (Mitchell, 2006). Because drinking pure water without electrolytes would
be further diluting the minerals in the body. Since every time people sweat during exercise, their
body will be losing sodium -- one of the most important electrolytes in regulating water reabsorption in the body. Thus, by drinking only pure water, people are further diluting sodium
content in the body. The body may eventually be unable to compensate for the loss of sodium,
which results in getting worse in dehydration (Mitchell, 2006). On the other hand, a research has
been found that people who drink fluids with electrolytes like Gatorade after exercise can help
replenish the sodium content in their body; hence, helps increase water re-absorption in the body
and prevent water losses from sweating. (Coyle, 2003). Thus, the goal of this experiment is to
test whether sodium does have a significant effect on water re-absorption back into the body
fluid, resulting in a decrease volume of urine among the people who drink Gatorade.
Methods and Materials
In this experiment, the subjects, including both Gatorade drinkers and water drinkers,
were required to obtain a sample of their own urine in every 30 minutes, with the total of 4
samples of each person. They were required not to eat any solid foods for 3 hours before the
experiment started. However, except for drinking caffeine and alcohol, all subjects were allowed
to drink any kinds of fluids. There were 12 people in this experiment, and each subject was
randomly chosen to drink either Gatorade (02 Perform) or water. Thus, 6 people who drank
Gatorade (blue) would be the experimental group, while the other 6 people who drank water
would be the controlled group. Each subject was required to drink a certain amount of the
assigned fluid. For instance, in order to calculate the amount of fluid intake, the subject was
required to multiply his or her body weight (lb) by 7 ml/lb. Besides that, each subject was given
a urine specimen cup and lid to collect his or her own urine in every 30 minutes. After each
subject calculated the amount of fluid intake and drank all the required amount of fluid at a
designated zone, he or she would go to the restroom to void bladder in every 30 minutes. After
each 30 minutes, the subjects would record the amount of urine by observing the urinemeasuring cup. This sample collection repeated until the subjects had collected for 4 urine
samples in 30 minutes, 60 minutes, 90 minutes, and 120 minutes. All the data from each subject
would be collected. For example, at each time interval (30 minutes each), the average values of
the six Gatorade drinkers and the six water drinkers were calculated respectively. And the
average value of each group in different time intervals would be used to draw a bar graph for
data analysis.
Results
Figure 1. The mean value of the urine volume for the six water drinkers at each time interval
(1:T30, 2:T60, 3:T90, and 4:T120) The error bar is also shown at each time interval.
Figure 2. The mean value of the urine volume for the six gatorade drinkers at each time interval
(1:T30,2: T60,3:T90, and 4:T120). The error bar is also shown at each time interval.
There were two bar graphs in total. One represented the experimental group (people
drank Gatorade), and the other one represented the controlled group (people who drank water).
In comparsion beween Figure 1 and Figure2, the results support the hypothesis that for the
people who drink Gatorade, the urine volume tends to decrease with an increasing time intervals
(Fig 2), whereas for the people who drink water, the urine volume tends to increase with an
increasing time inetervals (Fig 1). Thus, the data concludes that there will be an increase in urine
volume for water drinkers (Fig1), and there will be a decrease in urine volume for Gatorade
drinkers (Fig 2).
Discussion
For the people who drink Gatorade, they tend to have a decrease in urine volume with
increasing periods of time, as hypothesized. For instance, according to Figure 2, after people
drinking gatorade for 30 miuntes, the average value of urine output is 263 mL at T30 interval. As
time passes, the average value of urine output slightly decreases to 259 mL at T60 interval. And
eventually, the average value of urine volume decreases to only 133 mL, which the value is
almost half of the initial urine output at T30 (263mL).
In order to study whether drinking gatorade will have a significant effect on water
reabsorption in the body, people who drink water serves as a controlled group to compare the
result with the experimental group. Since water does not contain any electrolyte like sodium, the
data from Figure 1 supports the hypothesis that without sodium content in the water whereas the
gatorade does , the amount of the urine excretion tends to rise with increasing in time intervals.
A research also indicates that the electrolyte, sodium, plays an essential role in regulating the
water reabsorption ability into the body fluid (Mack, 1988). The reseracher explains that since
sodium can easily move across the cells through the transcellular pathway or through the tight
junctions between the cells, most sodium will therefore be reabsorbed from the proximal tubule
back into the blood. When most sodium was resborbed into the blood, the sodium concentration
in the body fluid will increase. As water follows salt, more water will therefore be reabsorbed
back into the blood by a passive physical mechansim called "osmosis", resulting in a decrease
volume in urine output. This mechanism is consistent with the hypothesis mentioned above:
drinking gatorade ,which contains a higher amount of sodium, helps conserve water retention in
our body. Apart from this, another article also explains that sodium can stimulate the realease of
antidiuretic hormone (ADH), resulting in an increase in the water permeability of the collecting
tubule (Guthrie, 2004). As the researcher says, when plasma osmolarity rises, the hypothalamus
will trigger the release of ADH from the posterior pituitary gland. When ADH reaches the
kidneys, it binds to membrane receptors on the collecting duct cells. Receptors activate the
synthesis of a second messenger cAMP. Signal transduction pathway occurs. More water
channels are therefore inserted into the cells of conducting cells, which enhances the water
permeability of the collecting duct. Thus, urine volume will be decreased (Guthrie, 2004).
Although this experiment supports the hypothesis that drinking Gatorade helps prevent
water losses from the body, further investigations are still required since the rate of sodium reabsorption and urinary excretion vary in person, depending on the needs of the body. (Anastasio,
2001). Furthermore, due to the existence of limitations in this experiment, such as a small
population size and limited time in collecting urine samples, there were a huge range of error
bars shown in both figures, which indicates that there is still a high uncertainty in the result. In
addition, since people might round up the digits in measuring the urine volume from the
measuring cup, there were limited significant digits for data analysis.
Reference Lists
1. Anastasio P, Cirillo M, Spitali L, Frangiosa A, Pollastro RM, De Santo NG. (2001). Level of
hydration and renal function in healthy humans. PubMed, 60(2), 48-56.
2. Bettinelli, Alberto. Bianchetti, Mario G. Simonetti, Giacomo D. (2009, Nov 19). Body fluid
and salt meatbolism. Italian Journel of Pediatrics, 35(1), 36.
3. Coyle, Edward F. (2003). Fluid and fuel intake during excerise. Journel of Sports Science, 22,
39-55.
4. Guthrie, David. Yucha, Carolyn. (2004). Urinary concentration and dilution. Nephrology
Nursing Journal. 31(3), 297-301.
5. Mack, GW. Nose, H. Nadel ER. (1988). Shift in body fluid compartments after dehydration in
humans. PudMed, 65(1), 318-324.
6. Mitchell, H. Kirven, Justin. (2006). Exercise-Associated Hyponatremia. Clinical Journal of
the American Society of Nephrology, 2(1), 151-161.