Water constitutes
55-60 % of the body’s weight. Interestingly, we can go weeks
without eating adequate calories, vitamins, and minerals, but only a
few days without water. From athletes to the average individual,
most people wonder how much water is needed. Although there are
several methods for estimating fluid needs, there is not a one size
fits all.
The Ins and Outs of Water
We ingest water in
only 2ways (excluding IV fluids). The water in our body comes from
the beverages and food consumed. Whereas fluid losses can be
contributed directly to urine losses (which are measurable) and
insensible losses (not easily measured) such as respiration losses
(think of blowing on a cold window and watching the condensation
collect), perspiration, and water lost in stool output. These
insensible losses account for about 1/3 of the total fluid output.
What’s water do anyway??
Water has many
functions in the body. The functions include: being a solvent for
the biochemical reactions that take place in the body, maintaining
acid and base balance (pH) in the body, releasing calories or energy
from the foods consumed in the diet, regulation of body temperature,
and growth of new tissue.
The body controls
the amount of water that is retained or excreted depending on the
concentrations of electrolytes, particularly salt.
How Much Water Do I Need?
There are several
ways of calculating water needs in the body. One of the simplest
calculations is using 1 ml/calorie consumed. This is fairly simple
if you know that 30 ml=1 fluid ounce. So let’s look at an example
of a person consuming 2000 calories/day (to meet their estimated
energy expenditure). Based on the formula of 1 ml/calorie consumed,
we could evaluate that this person needs 2000 ml/d. Most Americans
however are more comfortable using ounces, so we must do a tiny bit
of mathematical conversion as follows:
2000ml =
66.6 ounces AND 66.6 ounces = 8.2 cups water/day
30 ml/oz 8
ounces/cup
So, we see where the
8 cups of water per day rule comes into play. However, water needs
can sometimes be more, particularly if you are exercising, traveling,
visiting a higher elevation, living/working in a hot environment, or
having a bout of diarrhea. More fluid is needed during exercise and
in a hot environment primarily because of increased perspiration or
sweating. Flying on an airplane or visiting a higher elevation can
increase respiratory water losses. In fact, for every hour of air
flight, 2 cups of water is lost! And the water loss from increased
stool output can also be significant.
One of the best
rules of thumb for monitoring hydration levels is to observe your
urine output and color. When adequately hydrated, urine color should
be light yellow and frequent (ever 2-3 hours). Dehydration will
result in dark yellow to brown, concentrated urine in small amounts
that occur infrequently. Over hydration is seen with large amounts
of clear urine occurring often. Both dehydration and over hydration
can be significant and detrimental.
Help! I’m Parched!
Dehydration occurs
when there is inadequate fluid intake, often combined with increased
fluid expenditure such as sweating or from increased elevation.
Symptoms of dehydration often appear similar to other symptoms and
may be missed even by a health care professional if a complete
history is not taken. It is important to remember that the average
human body is 55-60% water and the body become symptomatic with even
small fluctuations and signals the brain to try to correct the
imbalances. The table below describes the symptoms associate with
the negative percentage change of the body’s water weight:
| Homeostasis (The body is 55-60% water) | No symptoms |
| 1-2% Loss | Thirst becomes increased |
| 4% Loss | Muscles lose strength and endurance, fatigue |
| 10-12% Loss | Heat intolerance, increase core temperature, weakness |
| 20% loss | Coma and Death |
It is always
surprising to hear of someone that dies of dehydration. How could
this happen? It happens because human beings are the only mammal to
ignore their own thirst. For example, let’s look at the family
dog. Let’s pretend that the dog’s water bowl has been depleted
and not refilled. The dog is thirsty. But the dog is unable to
verbalize to his owner that he is thirsty and becoming dehydrated.
The dog will seek out alternatives, such as drinking from the toilet.
Human beings on the
other hand, are very good at ignoring body cues, particularly thirst.
Let’s look at another example of a sixteen year old boy. The boy
is playing his first year of high school varsity football. It is
August in Texas. The heat and the practice are both more intense
than the boy has anticipated. He is thirsty, but the coach has
already announced that water breaks will only be allowed at his
discretion. The boy continues to ignore his thirst. Soon his body
is moving slower and with less power. If the player does not
rehydrate soon, his core temperature will continue to increase,
causing heat intolerance, and full body weakness. After the 20%
loss, the player will be comatose or dead. It becomes imperative to
respond to thirst and drink until that thirst is quenched,
particularly in these types of conditions.
My Cup Floweth Over…
Over hydration can
be just as critical of a situation. However, most of us don’t
think of this being too big of an issue and thankfully it is not,
except in certain specialized populations. Over hydration is also
known as water intoxication. When too much fluid is consumed in a
short period, it can overwhelm the kidneys, even fill the lungs, and
cause a severe sodium balance called hyponatremia, which literally
means low salt in the blood.
Hyponatremia implies
that there is too little salt in the blood, but this would be a
misnomer. Imagine three equal size clear containers (that represent
the human body). Each container is filled with 9 particles of sodium
chloride (table salt). One container is filled half way and this
first container represents normal hydration. There is an adequate
amount of sodium in the body, not too much or too little. In the
next container, the same 9 particles of sodium are present, but this
time, the container is only filled ¼ of the way. Here we have the
same amount of salt, but it is more concentrated because it has less
water or fluid. This represents dehydration or the condition known
as hypernatremia. This does not mean that too much salt has been
consumed, there are still 9 particles of salt in the solution.
Instead, there is simply not enough fluid. Finally, in the last
container, the same 9 particles of salt are present. This time, the
container is filled to the brim. This solution is very diluted. It
does not mean that the individual is salt deficient, but that there
is too much fluid in the body, creating the condition hyponatremia.
Back to the original
question…who is at risk for “over filling their container”? In
reviewing popular periodicals, newspapers, and journal articles,
there are a couple of groups that stand out. The first is
marathon/endurance athletes. Many of these athletes, even elite or
highly trained nonprofessional athletes, such as Boston marathoners
have fallen victim of the fluid trap. Why? They are afraid that
they will become dehydrated so they drink extra fluid to try to
offset their anticipated losses, and end up drinking too much. In
addition, they don’t want to stop and use the bathroom as this
might increase their finish time, so they hold it. Extremely thin
runners are at a higher risk because of limited fluid volume in the
body. In one study from the New England Journal of Medicine, some 488
Boston Marathoners were measured, weighed, and labs drawn pre and
post race. Researchers found that 1 in 8 had serious fluid and salt
imbalances. They found that in this population, some runners gained
between 4.5 to 11 pounds from drinking water along the route. (For
those not familiar with the marathon, it is 26.2 miles). To give
you an idea of what it would fill like to “carry” that much
fluid, imagine running with a gallon of milk (approximately 7 pound
of fluid)!
Another group that
was reported by The Dallas Morning News to have been overhydrated
were fraternity students involved in a hazing incident at Southern
Methodist University. According to reports, these students of Alpha
Phi Alpha fraternity were forced to drink hot sauce, followed by
gallons of water, and then struck by wooden paddles at an off campus
apartment. After the students were found to be unconscious, the men
tried to get them to vomit. Medical personal found them to be
severely overhydrated, demonstrated by hyponatremia and pulmonary
edema (water in the lungs).
Lastly, another
reported group to have some self-induced over hydration were
contestants on a radio game show trying to win a game system. They
were forced to drink and not urinate. The outcome resulted in kidney
failure and death.
Obviously, drinking
is important in adequate and balanced amounts. Again, fluid intake
should be dispersed throughout the day. More fluid may be needed
during special times such as exercising in a hot environment, but it
also important to be aware of the risks of over hydration and equally
important to pay attention to urination cues.
Hydration is vital
to maintaining optimal health and performance. For the an
individualized nutrition assessment, including fluid requirements,
contact Leslie Goudarzi, MS, RD, LD, Wellness Dietitian at Good
Shepherd Medical Center’s Institute for Healthy Living at
903-239-1551.
