Summer Sweat and
Salt
By Cathy Feiseler,
MD
Summer is here
with all of its heat and humidity.
Stories about heat stroke and
dehydration are in the news. Then, in
contrast, you hear a story about a
runner who became hyponatremic (low
sodium in the blood) and died from
drinking too much water. What's a runner
to do?
For years you have
heard that it is important to remain
well hydrated, especially during
exercise. Dehydration impairs the
function of all body systems, putting
the runner at risk for problems ranging
from poor performance to heat stroke and
death. Water is a great fluid
replacement drink... to a point. It is
possible to drink too much water and
basically dilute the body's levels of
electrolytes, especially sodium. This
said, it is important to remember that
dehydration is a much more common
occurrence. Thirst is a poor indicator
of hydration status; you may be 1-2%
dehydrated before you experience thirst.
So, what are you
supposed to drink? When you are not
exercising, water is fine. During
exercise lasting less than 60 minutes,
water is a suitable drink. Longer runs
are when things get somewhat
unpredictable.
People sweat at
different rates, ranging from a half
quart up to 4 quarts of fluid lost per
hour. Several factors determine rate of
sweat. Some people have more sweat
glands, so they produce more of this
fluid. Heat and humidity greatly affect
the rate at which sweat is produced.
Level of fitness also plays a role; as
the body adapts to exercise, especially
in a warmer environment, it produces
greater quantities of sweat during
exercise, as an adaptive response to the
heat that is produced by the exertion.
How do you figure
out how much sweat you produce? Weigh
yourself before and after a run. Each
pound that you have lost represents a
fluid deficit of 16 ounces. If you ran
for 30 minutes and lost 1 pound, you can
work on the premise that you lose about
a quart (32 ounces) of fluid each hour.
Plan on drinking an adequate amount of
fluid during longer runs to account for
this. This is a rough guide, since the
weather, especially humidity, will
affect the rate of sweat production on
any given day, but it should put you in
the right ballpark.
The concentration
of sodium is also extremely variable.
Often, as the body adapts to exercise in
the heat, the body produces greater
quantities of less concentrated sweat.
Despite this adaptive response, some
people seem to produce salty sweat.
Their shorts and skin are crusted in
white following a workout.
So what is an
appropriate replacement drink... sweat?
There are a number of sports drinks on
the market that contain electrolytes
(e.g. Gatorade, POWERAde, AllSport).
These drinks also contain carbohydrates
in a 4-8% concentration to improve taste
and supplement the decreasing supply of
this energy source in your body during
exercise. Replacing carbohydrates
becomes increasingly important as
running exceeds 60 minutes. The
concentration of carbohydrates in the
sports drinks does not compromise the
absorption of fluids in the
gastrointestinal system. More
concentrated sources of carbohydrates,
such as orange juice, will slow the
absorption process.
What about all of
the other additives in some sports
drinks? A combination of carbohydrates
and protein in a 4:1 ratio (like
Accelerade) has shown promise in
improving endurance when compared with
carbohydrate only drinks. The protein
stimulates insulin, which is involved in
the transport of energy into muscle and
in the conversion of glucose into its
storage form, glycogen. Carbohydrates
stimulate insulin, but ingestion of
increased amounts will decrease
absorption of fluids from the
gastrointestinal tract. The addition of
protein enhances the effects of insulin,
according to several studies.
Vitamins and
minerals have been added to some sports
drinks. Unless your diet is deficient in
these substances, they probably do not
improve performance. The amounts of
these substances in sports drinks do not
cause any problems.
Some drinks
contain supplements; typically, the
amounts present are lower than the doses
recommended to achieve their purported
effects. Be careful with supplements;
not all of them are safe (for example,
recent concerns about liver failure with
use of kava-kava). Research these
substances before you consider using any
of them. Enjoy your summer running by
staying well hydrated. Find a drink that
works well for you and drink up.
Warning
signs of dehydration
Excessive fatigue
Chills
Dizziness
Disorientation
Symptoms
of Hyponatremia (listed from least to
most severe)
Fatigue
Nausea
Headache
Confusion
Disorientation
Seizures
Dr. Cathy Fieseler
is the RRCA Sports Medicine Committee
chairperson. If you have questions for
Dr. Fieseler you can write her at
runmd@aol.com.
