called water intoxication, is generally the result of drinking excessive amounts
of plain water which causes a low concentration of sodium in the blood. Once a
rare occurrence at sporting events, it is becoming more prevalent as
participation increases and more novice exercisers are entering endurance
Prolonged and excessive sweating increases the risk that an
athlete will alter the delicate balance of blood-sodium concentration. Because
sodium is lost in sweat it is important for those exercising at high intensities
for long periods of time to replace any loses.
Research has found that long duration endurance events, such as
the Ironman distance triathlons, often have finishers with low blood sodium
concentrations. Those at most risk are those who are on the course the longest,
because they tend to drink the most water during the event. Runners who drink
extra fluids in the days before the race or those who stop at water stop during
the race are also at increased risk of hyponatremia. In fact, a study published
in the New England Journal of Medicine (April, 2005) found that 13 percent of
Boston Marathon runners developed hyponatremia from drinking too much water.
Causes of Hyponatremia
During high intensity exercise,
sodium is lost along with sweat. An athlete who only replaces the lost fluid
with water will have a decreased blood-sodium concentration. As an example,
consider a full glass of salt-water. If you dump out half of the contents of the
glass (as is lost in sweat), and replace that with water only, the sodium
concentration of in the glass is far less and the water is more dilute. This can
occur in the bloodstream of an athlete who only hydrates with water during
excessive sweating. The result is hyponatremia.
Adequate sodium balance is necessary for transmitting nerve
impulses and proper muscle function, and even a slight depletion of this
concentration can cause problems. Studies have shown that high intensity
athletes can lose up to 2 grams of salt per liter of sweat. Replacing this
during the event is critical to performance and safety.
Symptoms of Hyponatremia
The early warning signs are
often subtle and may be similar to dehydration and include nausea, muscle
cramps, disorientation, slurred speech, and confusion. At this point, many
athletes drink more water because they think they are dehydrated. Unfortunately,
water alone will increase the problem of hyponatremia. At the most extreme an
athlete may experience seizures, coma, or death.
Treatment of Hyponatremia
At the first sign of
symptoms an athlete should drink a sodium containing sports drink or eat salty
foods. Ideally, an athlete should plan ahead and estimate his or her fluid loss
and need for sodium replacement during the event, and stay on a hydration
schedule during the race. If the symptoms are extreme, a medical professional
should be seen.
The best way for an athlete to
avoid such problems is to plan ahead by training in the same conditions you will
encounter during race day. Hydration recommendations include:
Use a sodium containing sports drinks during long distance, high
intensity events (more than 60-90 minutes long).
Increase salt intake per day several days prior to competition (except
for those with hypertension).
Try not to drink more then you sweat.
During a marathon a good rule of thumb is to drink about 1 cup of fluid
every 20 minutes.
In the days before the race, add salt to your foods (provided that you
don't have high blood pressure and your doctor has not restricted your salt
Avoid use of nonsteroidal anti-inflammatory (NSAIDS) medicines that
contain sodium. Research suggests that these drugs may predispose runners to
Keep in mind that all athletes respond differently to exercise;
fluid and sodium needs will vary accordingly. Foods that provide additional
sodium include chicken noodle soup, a dill pickle, cheese, pretzels, and tomato
As always, it is important to consult your physician for special
considerations if you have a history of any health problems or are taking any
medication for a health condition.