Whether hiking in intense heat or running marathons, one has
to be concerned about hyponatremia. Symptomatic hyponatremia
is diagnosed as low sodium, and is caused by loss of sodium
due to drinking large volumes of water.
In reviewing the literature, there have been many cases of
low sodium with excessive fluid intake, especially after prolonged
exertion and excessive heat exposure. Pulmonary and cerebral
edema is not uncommon in severe cases. Dr. Murray from the
U.S. Army directly targets this, citing a 7-year study with
soldiers who experienced low sodium after excessive water
intake and sweat loss.
There are a variety of guidelines established to decrease
your risk for hyponatremia, as well as dehydration. Without
going into great detail, a rough guideline to follow when
in the wilderness and experiencing excessive heat and exertion:
Fluid intake should occur at the rate of approximately one
quart of fluid intake per hour, not to exceed 1-1/2 quarts
per hour, and not to exceed 12 quarts in a 24-hour period.
Of course the amount of heat and humidity, as well as the
amount of work being performed within any given hour must
be consideration, “work” being defined as running,
biking, or hiking. Other factors to consider include acclimatization
Healthcare Provider - Medical Treatment
It is important to differentiate between
hyponatremia, heat stroke, and heat exhaustion, as symptoms
may present very differently. To simplify, any heat illness
would most likely involve an increases core body temperature,
typically above 101 degrees Fahrenheit. In hyponatremia, the
temperature is usually normal. In heat illness and heat stroke,
the treatment of choice is rapidly cooling down of the body
by increasing fluid intake. In hyponatremia, fluid must be
restricted, with an increase in sodium intake.
1. Paul S. Auerbach, Wilderness
2. Thanks to Dr. Murray for his time spent with Survive
Outdoors staff in reviewing hyponatremia.