Hydration - WMI Curriculum Enrichment

Updated July 2006

By Tod Schimelpfenig
Curriculum Director – WMI of NOLS

Tod Schimelpfenig Curriculum Director – WMI of NOLS

How much water should I drink? What temperature is best? What about salt and sugar? There seem to be many answers to these questions. Opinions vary widely. The science is interesting, but it's relevance to our specific exercise or work patterns can be murky. If you don't like one answer you will surely find support for a different answer.

Here are a few bullet points:  

• Eat well and stay hydrated on a daily basis.
• Most people don't need to add sugar or salt. Plain water is fine.
• Monitor your urine output and color. 
• Drink before you are thirsty, and after your thirst is satiated.

If someone insists they stay hydrated on pop, pretzels and two liters a day - good for them. Active athletes often know what works for them, and that's fine. 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. Our advice has worked for years for NOLS students backpacking in the Wind Rivers, but it may not meet the physiological demands of the high altitude ultra-marathon runner.

How much should I be drinking?

Dehydration is been linked to everything from bad attitudes to altitude illness. In addition to preventing the s/s of dehydration, water balance helps our tolerance to heat, altitude and cold challenges.

You can estimate fluid loss by weighting yourself before and after exercise. You’ll have a sense of how much fluid you lose at that exercise rate and in those environmental conditions.

Many of the popular sources of information on this topic can be traced back to the position statement of the American College of Sports Medicine (ACSM).

The ASCM says "start drinking early and at regular intervals in an attemptto replace all the water lost through sweating." They recommend 250-300cc of water every 20 minutes during exercise.

This advice may not be practical for a wilderness backpacker. If I drink 300cc every 20 minutes while hiking I’ll drink almost a liter an hour. Over a 6 hour hike the 6 liter intake may be too much and a risk for hyponatremia. Three-four liters a day is still a good benchmark for backpacking in temperate conditions, as is clear and normal urine output.

Some experts say thirst is a sensitive indicator of the need to drink. Others say it’s not an accurate indicator of hydration status, particularly during strenuous exercise, when thirst sensors in both the throat and the digestive tract are inhibited. We still advise to drink before you get thirsty, and if you become thirsty, drink until after your thirst is quenched."

Dehydration is often cumulative. Inadequate hydration carries over from previous days in the field, and can lead to a more serious dehydration or electrolyte imbalance. When you are assessing for fluid balance (at “L” in SAMPLE) it may be wise to also ask about fluid intake over the past few days.

Should I add sugar to the water?

People argue whether sugar should be simple, complex or polymerized carbohydrate, and if it's needed at all. 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 ACSM does say that for exercise lasting less than 1 hour, there is little evidence of performance differences between consuming a carbohydrate-electrolyte drink and plain water. Participants in longer events should consider solutions containing 4%-8% carbohydrates.8

Factors Affecting the Rate of Gastric Emptying9

Should I take salt supplements?

It's fascinating how far this pendulum has swung. I was a school athlete when we gagged down large salt tablets on hot summer days. I was a NOLS Field Instructor when we issued rock salt and solemnly doled out a few crystals every day as a cure for all that ails you. I shudder when I remember drinking water and eating rock salt, and nothing else, during a multi day fasting "survival" expedition. No wonder I felt bad.

The pendulum then swung to the other extreme. Salt was bad. It caused high blood pressure and we didn't need it. We could thrive on the purity of water.

We now seem to be in the middle. Most people obtain ample salt with a balanced diet. Salty snacks when exercising hard may help.

People working hard and long in hot weather should consider salt supplements. Some ultra marathoners find they need to take salt tablets while they exercise. 5

The ACSM says "Inclusion of sodium (1/2 teaspoon/liter) during exercise lasting longer than 1 hour may be advantageous in enhancing palatability, promoting fluid retention, and possibly preventing hyponatremia in individuals who drink excessive quantities of fluid."

What should be the temperature of the water?

The most important impact of fluid temperature may be palatability. Some data seems to favor cool beverages over warm or hot, but the effect on gastric emptying would only impress a research scientist and would not have a noticeable impact in the real world.

What about sports drinks?

We no longer advise that sports drinks need to be diluted. Most of the sports drinks have acceptable concentrations of sugar, but on an individual basis people may like to dilute the drink for taste. Sport drinks may not provide enough sodium.

There is a difference between the "energy" drinks and sports drinks. The former are primarily stimulants, the latter have some value for sugar and electrolyte replacement.

Can you drink too much water?

There was an article in the fall of 2003 that received a lot of press and questioned the advice to drink 8 glasses of water a day. The article was focused on sedentary people. In the spring of 2004 the USA Track and Field Association (USATFA) released an advisory on proper hydration for distance runners which was picked up by a few newspaperss. Both publications raised questions about overhydration.

The USATFA notes that elite runners seem to drink less during races, are on the course for shorter times and have less hyponatremia. The runners on a course for more than 4 hours have the opportunity to drink more and this may increase their risk for hyponatremia.

The USATFA says that hydration is individual and ideally all athletes learn their rate of fluid loss and drink to match this loss. This marks a significant change from the standard advice to athletes to be drinking as much as they can to "stay ahead of thirst." The USATFA believes this advice may be promoting over hydration, especially in slower runners with more time to drink.

The formula for hyponatremia is relatively simple: salt loss in sweat exceeding salt intake plus water intake exceeding water loss equals lowered sodium level in the blood. When blood sodium gets too low, you have a case of hyponatremia.

Of critical importance in the assessment 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.

Patients with mild to moderate symptoms and a normal mental status may be treated in the field: Rest in shade with no fluid intake and a gradual intake of salty foods. If the patient has an altered mental status there is no question: They demand rapid evacuation to a medical facility.

Prevention is a matter of being sensible, which is so often the case. Drink lots, yes, but eat salty foods regularly while exercising in heat.

We often hear that coffee, or any beverage with caffeine, causes dehydration. Some folks say that every cup must be balanced with an equal amount of water. This is an exaggeration. Coffee is a diuretic, but a mild one. Nancy Clark, MS, RD wrote "The truth is, coffee and other caffeinated beverages in moderation are not health demons. Caffeine is one of the best-researched substances in the food supply. The overwhelming scientific evidence suggests that, in moderation, it has no adverse health effects (moderation means 1 to 2 mugs (10 to 20 ounces) of brewed coffee per day, or 3 to 6 12-ounce glasses of iced tea.). After exercise, caffeine is a poor choice for fluid replacement. The safest bet is to tank up on non-caffeineated beverages just after activity, and then later, if you so desire, enjoy your favorite caffeinated beverage in moderation."

General Sources
1. Wilderness Medicine.  4th ed.  Auerbach, P.S. ed.  2001. Mosby.  Pg 305-313.
2. Environmental Emergencies.  Stewart, CE.  1990.  Williams and Wilkens. 
3. Medicine for Mountaineering. 5th ed. Wilkenson, J.A. ed  The Mountaineers.  2001.
4. Physiology of Fitness 3ed Sharkey B.J  Human Kinetics 1990 pg 220-222.
Specific References
5. Exercise and Nutition in Hot Environments.  Askew, W.E.  1995.  Syllabus WMS Meeting April 1995. 
6. NOLS Nutrition Field Guide.  Howley, M.  NOLS 2002.
7. Williams, M. 1999. Nutrition for Health, Fitness and Sport, 5th ed. Boston, MA: WCB McGraw-Hill
8. American College of Sports Medicine:  Position stand on heat and cold-illness during distance running.  1996.
9. Lore of Running.  Tim Noakes, MD.  1991.  Leisure Press.  Champaign, Ill.  

Links (search under hydration or sportsmedicine and you'll keep yourself busy):
GSSI: The Gatorade Sports Science Institute  www.gssiweb.com/
Kevin Sayers UltRunR Site www.fred.net/ultrunr/
Hydration and fluid needs  www.sportsmedicine.about.com/cs/hydration/
American College of Sports Medicine www. acsm.org

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