Strange and Unexpected Facts About Altitude Sickness

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Last week I completed my first ever 14er when I summited Mount Elbert, Colorado’s tallest mountain at 14,433ft. While I’m an experienced hiker and this trail is considered one of the easiest of the Colorado 14ers, I was nervous because in the past I’ve had debilitating symptoms of altitude sickness, or Acute Mountain Sickness. I used to get nauseous, dizzy, achey, and extremely fatigued at around 9000ft, yet I had trouble sleeping. Anytime I visited my family in Colorado I would be out for the count for a few days, especially after trying to do anything active. Sometimes I didn’t feel right for weeks.

This time, I had no symptoms at all. I was certainly breathing hard and moving slow from about 12,000ft and up, but I didn’t feel ill. I wondered if maybe I would get hit with it at night or the next day; a delayed onset of altitude sickness after strenuous activity has happened to me before. Luckily, it never caught up to me and I’ve had no symptoms whatsoever in the following days.

This got me thinking about how strange altitude sickness is in general. As you’re probably aware, it doesn’t affect everyone the same way. An extremely healthy and active person may be knocked out by altitude sickness when increasing their elevation by just a few thousand feet, while a sedentary person from sea level may have no problem even after increasing their elevation tenfold. It also doesn’t always affect the same person the same way twice. The body doesn’t “remember” dealing with altitude in the past, so on each new trip, you will have to acclimate all over again. 

Every time I make a trip to a high elevation destination, even if I don’t get sick, I do still experience some health-related oddities and end up Googling facts about altitude sickness. These are some of the strange and unexpected effects of altitude sickness that I’ve learned about in the process.

You Need More Calories at High Altitude

I am always ravenous when I first arrive at high altitude. It takes a couple weeks for my appetite to calm down. I once read advice that when we’re at high altitude, it’s usually for a fun vacation, so we eat more as a result of a psychological or emotional shift and not a real shift in physical hunger levels. That advice seems dismissive. I know when I’m actually hungry! At least this person and this person agree with me. I get a lot of solace from random internet people.

I’ve read two theories on why we may feel hungrier at high altitude, though they are contested. One is that high altitude destinations are usually colder overall, so your body has to work harder and burn more calories to maintain your core temperature. The other is that your cardiopulmonary system has to work harder to deliver oxygen to your body at high altitude; increased heart rate and heavier breathing burn more calories. Both of these theories seem like common sense to me, but studies connecting these ideas to hunger levels are harder to come by.

Every study I find says that ghrelin levels decrease at high altitude and leptin levels increase. Ghrelin is the hunger hormone and leptin is the satiety hormone. People tend to lose weight at high altitude for these reasons (I have personally been surprised that I don’t seem to gain weight even though I feel I’m overeating). The metabolic rate also spikes at high altitude, meaning study participants burn more calories than usual at high altitude even without exercise. Only this last stat does anything to explain why I personally get so hungry at high altitude, while the ghrelin and leptin stats would seem to disprove my hunger theory. 

Contradicting me further are studies showing that high altitude triggers sensory changes. The Defense Centers for Public Health says that, “At high elevations dulled taste sensations (making food undesirable), nausea, or lack of energy can decrease the motivation to prepare or eat meals. Poor eating habits may also lead to constipation, aggravation of hemorrhoids, and undesired weight loss.” Anecdotally I do feel that for the first few weeks at high altitude, subtle flavors are not as appealing to me as bold flavors, which can lead me to pick garish junk foods over normal meals. There have been similar findings about the blandness of food in de-oxygenated environments like in space and on airplanes. Maybe it’s not so much hunger that I’m experiencing, as a dissatisfaction in the foods I’m eating and a desire for something more?

I suppose I could be confusing thirst with hunger, and of course dehydration is a major risk at high altitude. This would surprise me, though, because my main strategy to combat altitude sickness is to drink an absurd amount of water. I’m refilling Nalgene bottles left and right.

Regardless of hunger changes, one thing experts agree on is that increased energy expenditure at high altitude means you should be eating more, whether your appetite calls for it or not.

Reverse Altitude Sickness is a Thing

I am nomadic and move around every couple of months. Every winter I spend ~2 months at my parents house at 9000ft for Christmas. After the holidays, many times I will drive directly to sea level for my next adventure. I have been surprised that I get a bit of “reverse altitude sickness” where my body almost can’t handle the sudden gluttonous, decadent abundance of oxygen. This also happened to me after working a whole winter at Beaver Creek Ski Resort and then moving to Los Angeles.

It turns out this is a real thing, called high-altitude de-acclimatisation syndrome (HADAS). I haven’t experienced the length or severity of symptoms of the participants studied in China and Tibet, but apparently it can be quite debilitating. 

Higher Rates of Depression at High Altitude

When I was working at Beaver Creek and doing a work/housing exchange at a hostel in Colorado, I noticed a prevalence of people working the ski lifts and doing odd jobs in resort towns who seemed down-and-out or hard on luck. Many of my new friends were charming and vibrant, but seemed to struggle with their mental health nevertheless. Wealthy people come from all over the world to make merry while visiting beautiful mountain towns like Leadville or Vail, but locals trying to scratch out a living in these places are experiencing a very different reality.

I would expect the leading cause of mental health struggles in high altitude resort towns to be first and foremost a systemic result of capitalism and wage disparity, but some studies suggest a correlation between suicide rates and high altitude itself, regardless of demographic factors like income or race. I won’t make any irresponsible conclusions or assumptions; I simply think it’s interesting. You can read more about this here and here.

Smokers and Ex-Smokers Fare Better than Non-Smokers at Altitude

I feel so smug and vindicated by this fact because I am an ex-smoker (I quit years ago but still remember the judgment fondly). Ever since a friend told me about it, I’ve looked forward to spreading the good word. Apparently, smokers and ex-smokers fare better at high altitude than non-smokers because they are already used to pulmonary restriction. This study found that “Compared with non-smokers, smokers had a lower incidence of AMS and lower AMS scores than non-smokers upon arrival.” Ignore the part about impaired long-term results; just let us have our moment. This study found similar results that smokers have lower incidents of Acute Mountain Sickness. 

Of course, smoking and high altitude can be a dangerous cocktail in other regards. This study found that “residency at higher altitudes are associated with lower mortality from cardiovascular diseases, stroke and certain types of cancer,” but in contrast, “mortality from COPD and probably also from lower respiratory tract infections is rather elevated.” If respiratory illnesses are more common at elevation, combining that risk with those inherent in smoking cigarettes is an extra bad idea.

Smokers already know what they’re doing isn’t healthy, though, regardless of the elevation, so the important thing here is that there’s finally one point won by the smokers. Take that, squares.

Digestion Problems at High Altitude

While acclimating to high altitude, your body may de-prioritize less essential processes in favor of committing energy to cardiopulmonary processes. Your digestion may suffer as a result. Your colon may also feel the change in elevation, and while exercise is usually touted as a solution to help with regularity, at altitude exercise may actually make things worse.

This study lists so many potential issues that you’re likely to be able to blame any gastrointestinal symptom on altitude if you search hard enough. Try not to go too far down the rabbit hole that you end up diagnosing yourself with some rare form of altitude-induced stomach or intestinal cancer. Most likely you just have altitude-induced gassiness.

Can you think of any other weird effects of altitude sickness? Many of these don’t come up in search engine results about general symptoms of altitude sickness. They require highly specific keyword search terms to bring you to the depths of the internet, so I am sure other people have had similarly unexpected symptoms of altitude sickness that I’m not able to find because I simply haven’t thought of the right questions to ask. I’d love to hear your strange and unusual anecdotes!

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