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Hydration and Hyponatremia
By Tod Schimelpfenig, WMI Curriculum Director
How much water should you drink? Turns out, there's no clear answer.
Photo: Deborah Sussex

The cool weather of May and June that kept the snow in the high country has given way to summer temperatures, lush wildflowers and rivers full with snow melt. It brings to mind the need to stay hydrated.

Maintaining water balance, in addition to preventing dehydration, helps our tolerance to heat, altitude and cold challenges. Hydration is important to health, yet over-hydration can make us ill. The mantra of hydrate, hydrate and hydrate is heard throughout the wilderness world. This can be good, and it can be bad. As in anything, moderation is a good habit.

How much water should I drink? What temperature is best? What about salt and sugar? There are many answers to these questions depending on your physiology, activity and environmental conditions, and of course, on who you ask. The hydration needs of a sedentary and an active person will differ. We exercise at different rates, in heat and cold, dry air and humid air, at sea level and at altitude. Crafting one recommendation is challenging.

Competitive athletes can become very sensitive to exactly how much fluid they need. Some even weigh themselves before and after exercise to help figure out how much water they lose. We take the middle of the road and follow a recommendation from the American College of Sports Medicine to replace a minimum of 250cc of water for every 20 minutes during exercise, of a general target of 4-5 liters a day backpacking in the mountains. As you gain experience, you can fine-tune your intake. Monitor your urine output for color and quantity — dark urine is a sign of dehydration, as are fatigue, irritability, poor thinking, thirst and headache.

We sip hot and iced drinks, we drink cool and warm beverages. There is some data favoring the absorption of cool over warm beverages, but the differences would only impress a research scientist and probably don’t have a noticeable impact in the real world.

Likewise, most sports drinks have acceptable concentrations of sugar. Palatability seems as good a choice point as any. People argue whether sugar should be simple, complex or polymerized carbohydrate, and whether sports drinks provide enough sodium. This is primarily of interest to the competitive athlete. On a wilderness expedition, I don’t get my nutrition by gulping a drink or an energy gel at a race rest station. My daily carbohydrate intake is based on meals and on-trail snacks.

The emphasis on hydration has brought to light the dangers of over-hydration and hyponatremia — low blood sodium. The prominent examples in the press have been in Grand Canyon hikers and marathon runners. The hikers drink lots of water and don’t balance this with food — a source of electrolytes. The marathon runners are diligent in stopping at every drink station and ingest more fluid than they are losing through sweat.

Of critical importance in deciding if someone may have hyponatremia is an accurate history. Relatively little salty food intake combined with relatively high fluid intake, say several liters in the last few hours, should make you highly suspicious.

Prevention, to quote wilderness medicine guru Buck Tilton, is “a matter of being sensible, which is so often the case.” Drink lots, yes, but eat salty foods regularly while exercising in heat.

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