Altitude Sickness Prevention: Tips for Hikers and Travelers

Many people dream of climbing a mountain in Colorado or trekking in Nepal, but wonder how the high altitude will affect them. So in today's blog post, I'm going to share my favorite altitude sickness prevention tips.

My experience with altitude: I live in Denver (5,280 ft.) and regularly climb above 14,000 ft. on the local peaks. I've also climbed Huayna Potosi (19,974 ft.), Kilimanjaro (19,340 ft.), Pequeno Alpamayo (17,749 ft.), Iztaccihuatl (17,159 ft.) and Mount Ararat (16,854 ft.).

Interestingly, one of my most miserable intense high-altitude experiences involved driving to the Rongbuk Monastery in Tibet (16,340 ft.) and staying overnight. More on that in a minute.

Huge disclaimer (flash, flash)

None of the above makes me a doctor. Before heading to altitude, it's a good idea to visit a travel clinic or work with a doctor who knows your well. This is doubly true if you have an existing medical condition or if you will be taking medications to prevent altitude sickness (more on that in a minute).

What is altitude sickness, anyway?

Altitude sickness actually has three forms. Many travelers to high-altitude develop symptoms of acute mountain sickness, or AMS. These include headache (most common), upset stomach (including vomiting), tiredness, dizziness, lightheadedness, and difficulty sleeping.

Many people compare AMS to a really bad hangover! But while it feels gross, it usually goes away by itself with proper self-care.

When I talk about "altitude sickness" in this post, I'm generally referring to AMS. However, there are two other types of altitude sickness you should be aware of.

If you're a fan of mountaineering disaster books, you may be familiar with two more severe forms of altitude sickness:  HAPE (high altitude pulmonary edema) and HACE (high-altitude cerebral edema). These involve accumulation of fluid around the lungs and brain, respectively.

HACE and HAPE are rare compared to AMS. However, they're emergencies that require immediate descent and medical attention.

Read more about all three kinds of altitude sickness at the Institute for Altitude Medicine website.

Why does altitude sickness happen?

Contrary to popular belief, oxygen molecules make up 21 percent of the air at high-altitude, just like they do at sea level. However, because atmospheric pressure is lower, those oxygen molecules are spaced further apart.

This means that you breathe in fewer oxygen molecules with each breath. As a result, less oxygen gets carried by your blood to your cells, including your working muscles.

The process of digestion requires a lot of oxygen, which explains why many people experience stomach upsets at altitude. Sleep disturbances may be related to increased heart rate or low levels of carbon dioxide. (At very high altitudes, some people actually stop breathing for a few seconds during sleep and wake up feeling oxygen starved.)

Science still isn't sure exactly why low atmospheric pressure causes headaches.

At what elevation does altitude sickness start?

Many hikers from low elevations start feeling noticeably more winded around 5,000 ft. Some people also notice subtle changes in their vision (especially poorer night vision).

Susceptible individuals may start to feel ill around 6,000 ft. About half of people who spend time above 8,000 ft. report a headache or other altitude sickness symptoms.

HAPE and HACE are most common among people who spend time above 10,000 ft. and 12,000 ft., respectively.

How long does it take to get altitude sickness?

When you arrive at high elevation, your body almost immediately adapts by increasing your breathing rate, heart rate, and blood pressure. Within a few hours, you start producing additional red blood cells to capture and transport oxygen. If you stick around for a week (and especially for a few months), your body will make amazing adaptations.

However, there's a gap in time where you physiology hasn't really caught up with reality. Altitude sickness symptoms tend to appear within 24 hours of arrival at elevation and last for 1–2 days (assuming no further gain in elevation).

Will I get altitude sickness in Colorado?

In one study, about 60 percent of people sleeping above 9,800 ft. (approximately the elevation of Breckenridge and Copper Mountain) experienced altitude sickness symptoms.

If you're arriving from low elevation, you can significantly reduce your chances of developing altitude sickness by spending a day in Denver, Boulder, or Colorado Springs before heading to the mountains.

Many people find they can hike to high elevations for a few hours (to the summit of a Colorado 14er, for example) without developing altitude sickness. The key is to take it slow. Taking a day to acclimate before the big climb can also help.

Is it possible to prevent altitude sickness?

Not always. Certain people seem to be more genetically prone to altitude sickness. Research suggests that naturally shallow breathers may be especially at risk.

However, you can reduce your chances of developing debilitating altitude sickness by training properly, taking extra time to acclimate, ascending slowly, and practicing good self care.

Can proper training reduce my chances of getting altitude sickness?

To some degree, yes. Research involving people indigenous to high-altitudes (think Sherpas and Tibetans) suggests that they have a naturally high VO2 Max. This means their bodies are very efficient at using the small amounts of oxygen in the air.

Some cardio training guidelines for hikers, trekkers, and climbers headed to high-altitude:

• Always start by building a good aerobic base with long, slow distance (3-4 effort level on a scale of 10). One of these workouts should be your "long" run or hike and account for about 30 to 50 percent of your total training volume. No matter how advanced you get, 70–80 percent of your training should be at this intensity.

• Once you're doing about three hours of long, slow distance workouts a week, add some tempo runs or long intervals to push your lactate threshold. These should be done at a 6-7 effort level 1–2 times a week. (What's a lactate threshold? To learn more, check out my post on heart rate training zones.)

• When you're training successfully for about 7 hours a week, add a high-intensity interval workout that pushes your VO2 max. Gradually decrease the rest time between intervals so that your body learns to tolerate a build-up of hydrogen ions in your blood.

Some additional mountaineering training resources you might find helpful:

• How to get in hiking shape when you're starting from zero – blog post for brand new beginners

• Workouts to prepare for altitude – intermediate to advanced

Need help making your High-altitude training plan?

My FREE Training Plan Workbook walks you through a simple, six-step process to help you design a fitness program that gets results. Fill out the form below to get your copy.

How can I prevent altitude sickness while hiking and climbing?

Here are some helpful altitude sickness prevention tips I've gathered from fellow mountaineers, guides, and my own experience.

• Take time to acclimatize. It's worth burning a few vacation days to spend some time relaxing at moderate and then high elevations before attempting your goal climb. If possible, try to hang out (or take easy day hikes) above 8,000 ft. for at least three days before attempting the main event.

• On any given day, don't sleep higher than 1,500 ft. above your previous camp.

• Take it super slow. Your entire ascent should be at a conversational pace. If you're gasping as you talk to your buddy, slow it down. Interestingly, the people who are most likely to develop altitude sickness appear to be the young and fit. This is probably because they tend to climb faster than others on the team.

• Drink plenty of water, but don't over-hydrate. Two to four liters per day is sufficient for more people at altitude.

• Avoid alcohol and sleeping pills containing benzodiazepines (most commonly, Benadryl/diphenhydramine). They can worsen your sleeping difficulties. If you're concerned about sleep or jet lag, ask your doctor about appropriate high-altitude medications.

• Decreased appetite and stomach upset can be issues at altitude. During your acclimatization period, eat small meals frequently. Carbohydrates tend to be easier on the stomach than fats and proteins. Bring some delicious snacks from home that will tempt you even if you're not hungry.

How do I treat altitude sickness if I get it?

The most effective cure for altitude sickness is to descend. Going down just a few hundred feet can make a huge difference. If it's not possible to descend, rest at the same elevation (and definitely don't attempt to sleep higher).

During your illness, practice good self care. Get plenty of rest. Try to drink fluids and eat what you can. You may feel really hung over ill, but keep in mind that most people with AMS feel better in a day or two.

While most cases of altitude sickness get better on their own, be alert for symptoms of HAPE and HACE, especially if you're over 10,000 ft.

Medications like Diamox may be helpful in treating altitude sickness, as we'll see in the next section.

Should I take altitude sickness pills (Diamox/acetazolamide)?

Until recently, altitude sickness medications were rarely used by hikers other than Nepal trekkers and high-altitude mountaineers (climbing above 16,000 ft.). But in the past few years, I've gotten a ton of questions from readers and mountaineering students wondering if these drugs could help them when climbing Colorado 14ers, Mount Rainier, or other relatively low peaks.

This question tends to inflame passions in the mountaineering community. Just ask a few experienced mountaineers and you'll see that many have strong opinions on the subject!

Here are the pros and cons I've heard from my high-altitude guides in Bolivia and Washington. (The Washington guide was a Mount Everest guide.)

Pros

• Medications like Diamox are somewhat effective at preventing altitude sickness when other best practices (slow ascent, etc.) are followed. For best results, begin taking the medicine 1–2 days before arrival at altitude.

• Even if you don't take it as a preventative, you can use Diamox to treat altitude sickness if you develop symptoms. Be sure to ask your doctor or pharmacist what dosage is right for you in this case.

Cons

• The number one complaint that most experienced guides and mountaineers have about Diamox is that it isn't a magic bullet. You can achieve the same benefits without the annoying side effects (increased urination, tingling extremities) by acclimatizing properly, ascending slowly, hydrating, and eating small, carbohydrate-rich meals.

• According to the guides, Diamox can temporarily mask symptoms of distress at altitude. Someone who is experiencing mild altitude symptoms while taking Diamox can suddenly become quite ill when exerting on a hike or climb. For this reason, guides tend to be more conservative with clients on Diamox.

• Plain and simple, Diamox is absolutely no replacement for acclimatizing properly and ascending slowly (1,500 ft. per day between camps). Never use it to "push" your acclimatization beyond the recommended schedule.

Personally I've climbed with and without Diamox. I do feel that taking Diamox preventatively improves the quality of my appetite and sleep when I'm above 14,000 ft. for an extended time.

However, it definitely has its limits! At the Rongbuk Monastery in Tibet, two of us were on Diamox, one was not, and all three were completely miserable. (We drove up, so this will be less of an issue for hikers and climbers.)

How can I treat or prevent altitude sickness naturally?

There's some evidence that gingko biloba supplements can help to prevent altitude sickness when started about five days before the climb. However, it's difficult to replicate this study because supplements vary in quality and potency.

As you travel around the world trekking and climbing, you'll find that many cultures use foods and herbs to prevent altitude sickness. Tibetans drink yak-butter tea. South Americans chew coca leaves and drink coca tea. Maybe some of these natural remedies will work for you. At the very least, trying them will be a fun cultural experience.

So there you have them, my best altitude sickness prevention tips.

Do you have any tips to add? Comment below to share.

Originally published Nov. 18, 2018.