Hyponatremia in distance athletes: How to avoid water intoxication
By
Jon Englund, MD, Sports Fellowship Trained Family Practice Physician
Hyponatremia is a condition where the concentration of sodium (i.e.,
Na) in the blood becomes dangerously low (<135 mmol/L). In the distance
athlete, it most commonly occurs by overzealous water consumption
resulting in the dilution of blood and a decreased sodium concentration.
Rarely, it can be caused by sodium depletion due to excessive sweating
in conjunction with fluid replacement from a liquid that has a lower
sodium concentration than the athlete's own sweat.
Although most hyponatremia is mild, its occurrence is relatively
common. The incidence of hyponatremia has been measured at 5-18% of
participants in U.S. marathons over the last several years. This number
appears to be decreasing as education about hyponatremia improves.
Who's at risk for hyponatremia?
Distance athletes participating in events longer than 3-4 hours
Slower athletes having more time to consume fluids assume an
even greater risk
Inexperienced participants, often educated to “drink plenty of
fluids to stay hydrated” exhibit a higher risk
Participants in races with a high availability of drinking
fluids are at increased risk
Additionally, low body weight, female sex, and use of
non-steroidal anti-inflammatories have been found to be risk
factors.
Unfortunately, symptoms of hyponatremia are similar to those of other
medical conditions that affect distance athletes (i.e., heat illness,
dehydration and exercise-associated collapse). Symptoms of hyponatremia
include fatigue, light-headedness, weakness, cramping, nausea and
headaches. Symptoms of severe hyponatremia include
confusion/disorientation, seizures and coma.
The diagnosis of hyponatremia involves an exam to screen for the
other conditions listed above. Patients with a normal rectal temperature
and without signs of dehydration need a rapid blood test to check their
sodium concentration. Rapid blood tests can be done at race sites with a
turn around time typically less than 10 minutes.
Mild hyponatremia can be treated with the avoidance of water intake
and the liberal use of salt in the post-race setting. Moderate to severe
hyponatremia is treated by the intravenous administration of hypertonic
saline (i.e., fluid with a high concentration of sodium).
The key to prevention of hyponatremia is to avoid overdrinking. Since
sweat rates and sweat sodium concentration vary greatly among
individuals and are affected by environmental conditions, it is
difficult to make recommendations about how much fluid one should
consume during competition.
There are 2 strategies generally recommended to determine how much
fluid one needs to replace. The 1st strategy is to drink to thirst. This
is a reasonable approach assuming that fluids can be easily accessed
throughout the competition. The 2nd strategy is to calculate your
individual optimal hydration rate. This can be done using a method
described on the USA
track and field Web site.
Healthy tips
Consumption of salty snacks before and during the race can help
protect against hyponatremia.
Drinking sports drinks does not eliminate the risk of
hyponatremia. Although sports drinks have some sodium, the
concentration is still less than the sodium concentration of blood.
“Overdrinking” of sports drinks can still cause hyponatremia.
However, they do have some electrolytes, including sodium and
carbohydrates, and are recommended as the drink of choice (vs. plain
water) for distance exercise lasting longer than 1 hour.
For questions on hyponatremia or other sports medicine topics, call
the Aurora Sports Medicine Hotline at 414-219-7776 or 800-219-7776.
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