Hydration is key to performing well in endurance sports, in everything from mountain running to rock climbing. In Training for the New Alpinism, Steve House and Scott Johnston advocate starting climbing days well hydrated and carrying much less water than you might think necessary—certainly less than was considered normal at the time the the book was published. Their sound advice has changed the way many mountaineers hydrate. The simple fact is that the weight of water often limits how much a climber can carry. And with access to fluids often limited at high altitude, the problem is further exacerbated.

In this article I want to expand on Steve and Scott’s original advice and provide several hydration tips that can help alleviate severe dehydration on any big mountain day, whether you’re training or racing.

Hydration for Endurance Sports: Is Water Sufficient?

First we need to establish that simply drinking to thirst when out on the mountain should be sufficient to offset any significant level of dehydration that would be detrimental to performance. However, in situations where free access to fluids (to top up your water bottle) is limited, or when urination breaks are undesirable, choosing a drink that has greater energy and sodium content will promote longer-term fluid retention.

Anecdotally, mountaineers I work with have reported consuming as little as 500 milliliters of water per day and carrying a maximum of around 2 liters at any one time while out on the mountain. If you are able to drink to thirst with sufficient access to fluids, then drinking water will be sufficient. However, during long days in the mountains when you may not have access to enough fluids to continue drinking to thirst, then consuming more than just water may in fact aid the absorption of fluid.

The Detrimental Effects of Dehydration

Why is dehydration a problem? Dehydration when sufficiently severe will have an adverse effect on mood, as well as on mental and physical performance. This can impair decision-making, cause early fatigue, and increase perceived effort, meaning the physical and mental tasks at hand feel harder to do. Taken together, these can compromise safety and your enjoyment of the day.

Fun fact: Attention to hydration was cited as contributing to the first successful attempt to summit Mount Everest.

Individual Factors Affecting Fluid Loss and Hydration Requirements

Factors that affect how much fluid you lose from sweating include your sweat rate, your level of fitness, your physical exertion, how much direct sunlight you get, the glare from the snow, and your layering. At high altitude, water loss is significantly increased due to the dry air and your increased rate of ventilation to maintain tissue oxygenation.

It is important to get used to your own fluid requirements! Estimating your own fluid needs is best done through experience. Practice drinking to thirst or devise a hydration strategy during training, before you head out up high. Consider the environment you will be in, how long you will be out for, and your access to fluids.

Best Fluid Choices

The formulation of your drink will affect the rate at which you absorb the water content. The amount of fluid that you drink at once will also influence how much fluid is absorbed. If you consume a large volume at once, you will retain less of it.

The beverage hydration index study cited below showed that drinks with higher energy and sodium content help the body retain more fluid compared to drinking water alone. This study demonstrated that the beverage hydration index for milk, orange juice, oral rehydration solution, and full-sugar Coke is significantly higher 2 hours after ingestion compared to water. What this means is that the body retains more fluid 2 hours after you consume those drinks (ones with a higher beverage hydration index) than after you drink the same volume of water.

If you know your fluid intake is going to be compromised on big days, these drinks with a higher beverage hydration index could prove beneficial to offset severe dehydration.

Practical Tips for Hydration in Endurance Sports

1. Consider the scenario you are entering.

Will you be able to drink to thirst or will you only be able to drink during opportune breaks?

2. Get to used to your own fluid requirements.

Think about your past experience of hydration in the mountains and consider: What could I have done differently?

3. Focus on hydration before the trip.

In the days leading up to a mountain trip, aim to maintain hydration. Sip on fluids throughout the day and monitor your urine output and color. Your urine should be a pale straw color.

4. Start your mountain day hydrated.

If you set off dehydrated, you are already on the back foot. You face an increased likelihood of severe dehydration, which can result in impaired physical and mental performance. Including a glass of milk or orange juice with your breakfast, or having a milky coffee, will help you retain more fluid and reduce your need to go to the toilet before setting off.

5. Drink to thirst.

Relying on thirst and your habitual drive to drink may be sufficient. But at altitude having a planned hydration strategy could go along way toward offsetting severe dehydration. Be deliberate about taking a mouthful of fluid in opportune breaks throughout the day. Consider premixing a drink that has higher energy and sodium content (e.g., 200 milliliters of fresh fruit juice, 300 milliliters of water, and a pinch of salt). If you carry two soft flasks, perhaps fill one with water and the other with a sports drink. Always practice prior to your main event!

6. Eat and drink water together.

Whenever you eat something, take a mouthful of water to wash it down. The energy and salt content of your food will help you retain more of the water.

7. Swish water around your mouth.

When fluid supplies are low and you want to preserve water for the rest of the day, take a mouthful of fluid, swill it around your mouth, then swallow (similar to using a mouth rinse after brushing your teeth). This sensation of fluid around the mouth can have a positive sensory effect.

8. Rehydrate at the end of the day.

This is important, particularly if you have a short time frame. Drink a glass of milk, a Coke, a recovery shake, or a hot chocolate immediately once you’re off the mountain. Have a glass of fruit juice or milk with your next meal. Sip regularly on water until approximately 30 minutes before bedtime.

9. Consider drinking an oral rehydration solution.

This can be helpful if you feel extremely dehydrated once you’re off the mountain, or when you have consumed only a small amount all day with a short turnaround until you are climbing again.

10. Pick a hydration system that works for you.

Use a hydration system that will encourage you to drink and is easy to carry—whatever you prefer and whatever works best for you. Nalgene bottles and soft flasks are popular choices.

To summarize: When you are going to have limited access to fluids and a tight window for rehydration, consider making the most of the fluid you drink using the strategies outlined here.

-by Rebecca Dent, Uphill Athlete High-Performance Dietitian

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References and Further Reading

• Benton, D., et al. “Executive summary and conclusions from the European Hydration Institute expert conference on human hydration, health, and performance.” Nutrition Reviews 2015 Sept;73(suppl 2):148–150. https://doi.org/10.1093/nutrit/nuv056.
• Hoffman, Martin D., Trent Stellingwerff, and Ricardo J.S. Costa. “Considerations for ultra-endurance activities: part 2 – hydration.” Research in Sports Medicine 2018 July;27(2):182–194. https://doi.org/10.1080/15438627.2018.1502189.
• Maughan, Ronald J, Phillip Watson, Philip AA Cordery, Neil P Walsh, Samuel J Oliver, Alberto Dolci, Nidia Rodriguez-Sanchez, and Stuart DR Galloway. “A randomized trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index.” The American Journal of Clinical Nutrition 2016 Mar;103(3):717–723. https://academic.oup.com/ajcn/article/103/3/717/4564598.