Hyponatremia in Hikers (comments welcome)

A few months ago a very good article by the GSMNP Service was forwarded to all hikers by Tom Wainer concerning problems such as heat exhaustion and heat stroke. There is another problem that can be associated with heavy exertion in hot and humid weather; the problem is hyponatremia. Hyponatremia is an abnormally low concentration of sodium in your blood; it has also been referred to as water intoxication.

Although organic conditions can be the prime cause of hyponatremia, its occurrence in athletes was first written about in 1985 after it was noted that ~30% of the athletes competing in the 1984 Ironman Triathlon had symptoms of hyponatremia. The causes include excessive sodium losses (e.g., sweating & urination) and replacement with sodium-free fluids. Heavy exercise typically exceeding four hours in hot and humid weather sets the stage for hyponatremia; this is one reason why novice marathon runners are much more apt to have a problem with it than elite runners.

How does this relate to hiking? Even though our 20-mile+ hikes may not be as stressful as running a marathon, they take a bit longer than 4-hours; furthermore, I don’t think that that hikers train for their hikes quite like runners train for their races. Thus even though I have not read of a hiker sustaining hyponatremia, I posit that the challenges to the typical hiker-trained body could cause hyponatremia if one is not careful. I became interested in this topic after another hiker told me of an incident wherein a hiker collapsed on a particularly arduous summer hike; I felt his description fit the definition of hyponatremia (muscle weakness & cramps could be symptomatic too). On one of my long hikes I became flat-out scared when a cohort filtered and chug-a-lugged ~3 liters of water from a stream; all I could think of was hyponatremia and we were ~8 miles from hike terminus. (The electrolyte Stamina was subsequently given in both cases.)

If you take a long hike in the summer, the fluids that you drink should contain electrolytes (e.g., sports drinks). Sodium is a required element for normal body functions but it is lost in sweat and urine; if it not is replaced in the diet and excess water is drunk, theoretically this can upset body chemistry to the point that hyponatremia results. In addition to a sports drink, I also carry electrolyte Stamina packets (each contains 134 mg. sodium) for first aid purposes (it can be mixed with most any drink). Sports drinks and salty foods should negate the need for salt tablets (e.g., 8 oz. Gatorade has 110 mg. sodium, one Baked Rold Gold Hard Sourdough pretzel contains 220 mg.).

Wendell Liemohn

Sources: MayoClinic.com; medlineplus; McArdle, W.D. et al.: Exercise Physiology—Energy, Nutrition, and Human Performance, Lippincott Williams & Wilkins, 2001; Porth, C.M.: Pathophysiology—Concepts of Altered Health States, Lippincott Williams & Wilkins, 2002.