I'd be grateful for any views on the risk of sustaining permanent structural and cognitive changes from a climbing trip to high altitude (5000-6000m) if acclimatisation is reasonable and no HACE/HAPE develops. Every paper on the subject seems to say something different about the risks. Clearly at the extreme end (multiple 8000m peaks with no O2) you'd expect to find stuff on MRI. But would e.g. Kilimanjaro or Nepali or Andean trekking peaks in the 5000-6000m range also risk permanent damage? The famous Fayed 2006 study that Scientific American has been disputed in some quarters e.g. by high altitude medicine specialist Dr Peter Hackett - his basic premise in a podcast I listened to was that'if you want to retain every single brain cell, don't climb 8000ers' but that he doubted the studies showing major damage below that.

It's very hard to make a risk informed decision about trips to that kind of altitude based on the papers I've read. Obviously you have to accept the risk of severe AMS, but my question is more about whether even apparently straightforward ascents with little AMS symptoms also risk substantive brain changes?

Some relevant papers:

Fayed et al 2006 paper that was extensively picked up in the media but did not do pre expedition MRI: https://www.semanticscholar.org/paper/Evidence-of-brain-damage-after-high-altitude-by-of-Fayed-Modrego/f182e5c8a73b505e66e50bcb671ee8cf86c0f6f5

Fan et al paper on reversible abnormalities https://www.nature.com/articles/srep33596

Kotke et al paper finding limited evidence of structural damage (Morphological Brain Changes after Climbing to Extreme Altitudes--A Prospective Cohort Study) https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0141097

Dr Peter Hackett study on Denali - https://www.boulderweekly.com/adventure/this-is-your-brain-this-is-your-brain-at-altitude/

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    If you want to keep all your brain cells, don’t drink a beer while swapping mountaineering stories with your pals…
    – Jon Custer
    Commented Jan 19, 2022 at 17:03
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    "Every paper on the subject seems to say something different about the risks." Then that is probably the answer. We maybe just don't know. Then it just becomes a personal assessment of your own risk tolerance given the unknown.
    – noah
    Commented Jan 19, 2022 at 17:42

2 Answers 2


This is a good question that I am only partially qualified to answer, mainly because I have looked into it in some depth. A full answer can be given by a medical professional with actual working experience in high altitude - this is a very small group of researchers or some medics from the Indian/Chinese armies. That being said,

First of all, 6000M is not that high and certainly not extreme. So let's talk about 8000M.

From the first paper you linked to

Only 1 in 13 of the Everest climbers had a normal MRI; the amateur showed frontal subcortical lesions, and the remainder had cortical atrophy and enlargement of Virchow-Robin spaces but no lesions. Among the remaining amateurs, 13 showed symptoms of high-altitude illness, 5 had subcortical irreversible lesions, and 10 had innumerable widened Virchow-Robin spaces. Conversely, we did not see any lesion in the control group. We found no significant differences in the metabolite ratios between climbers and control

So Fayed et al concluded that

We conclude that there is enough evidence of brain damage after high altitude climbing; the amateur climbers seem to be at higher risk of suffering brain damage than professional climbers.

The second paper you linked to doesn't actually consider "high altitude". Fan et al are looking at the Tibet plateau, which is around 4500M in elevation and there are humans living there all year round (nomadic tribes and Chinese soldiers). Not surprisingly, the physiological effects are less pronounced.

The BoulderWeekly article states

Of the 12 professional climbers and one amateur in the Everest expeditionary group, 11 climbers’ MRIs indicated evidence of brain atrophy, a decrease in the size of the brain, and the enlargement of fluid spaces surrounding the brain vasculature.

and further on

Only the amateur’s image indicated brain lesions after suffering symptoms consistent with acute mountain sickness (AMS) and high altitude pulmonary edema (HAPE). One professional mountaineer’s image demonstrated normal MRI results with no atrophy or lesions.

So I understand that as everyone suffers from brain atrophy while only amateurs (climbers who are not acclimatized) suffer from irreversible lesions.

The Kotke paper concludes

A single sojourn to extreme altitudes is not associated with development of focal white matter hyperintensities and grey matter atrophy but leads to a decrease in brain white matter fraction. Microhemorrhages indicative of substantial blood-brain barrier disruption occur in a significant number of climbers attaining extreme altitudes.

Again - consistent with atrophy in all cases. And lesions in some.

Additionally, you must consider the work of John B. West, who has been working in high altitude medicine for many decades now. From this paper

Impairment was manifest by deficits in memory storage and recall, aphasia, concentration, and finger tapping speed; the last deficit was still detectable a year later in one group of mountaineers.

From this other paper by the same author

However, there is impairment of central nervous system function at high altitude which persists following return to sea level. Significant abnormalities of motor coordination persisted for more than 12 months in most members of the Everest expedition

followed by

There is evidence that the climbers who ventilate most at high altitude have the most central nervous system impairment, presumably because of the more severe cerebral vasoconstriction.

So this probably answers your question. There are long term effects in all cases. Amateurs (unacclimatized climbers) suffer the most.

However, there are many examples of mountaineers coming back to live normal successful professional lives. So how severe the long term after effects are is something that varies.

You could also consider people who have done Mt Everest without supplemental Oxygen and find out how they are doing. (Reinhold Messer few decades back to Adrian Ballinger more recently). Afaik, Ballinger is still active in his profession though Messner is retired after a long career post-Everest.

But would e.g. Kilimanjaro or Nepali or Andean trekking peaks in the 5000-6000m range also risk permanent damage?

No, it would not. Your SpO2 will reduce while you are at that altitude; AMS, sure it is common, but nothing long term. Hundreds of people do 6000M peaks in India/Pakistan/China/Nepal with no long term brain effects. Very rarely do people suffer from cerebral edema at these altitudes, but it happens, and that's a bigger risk you should be aware of. However, edema doesn't onset suddenly, so as long as you are aware of symptoms, and start to descend at the right time, you'll be fine.

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    Well considered answer, thanks! I would tend to agree with you that given the volume of people reaching 6000m annually, there would likely be evidence by now (even if anecdotal not long term studies) if there were major cognitive effects from a single exposure. Incidentally, 'extreme' altitude is generally defined in medicine as 5,500m+. I agree with you, having read John Hunt's book and heard Hillary's interviews into old age, they didn't show many signs of obvious cognitive deficits. But maybe professional mountaineers are biologically better suited to HA. Commented Jan 20, 2022 at 8:00
  • But the Fayed study is definitely concerning. I don't have much white matter to spare... Commented Jan 20, 2022 at 8:04
  • Sorry additional comment. A lot of the studies seem to feature inadequate acclimatisation. For instance the Kotke paper on Himlung Himal (7100m) saw the climbers get to camp 2 (6025m) after only 11 days. A normal acclimatisation might see them reach base camp (4850m) at that time. Commented Jan 20, 2022 at 9:33
  • The acclimatization schedule is sometimes shortened, especially on lesser peaks, and by commercial teams on a budget, or experienced mountaineers who are pre-acclimatized. If you check the Joh West papers, a lot of his work is on Everest expeditions (which almost always have lots of time to acclimatize), he still talks about residual impairment.
    – ahron
    Commented Jan 20, 2022 at 10:28
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    The physiology of elite mountaineers is similar to that of elite endurance athletes. Most average mountaineers are about as fit as an average athlete. So not much physiological advantages. The sherpas are a little different. Nirmal Purja of the Gurkhas for instance recently did the 14 summits in 7 months, where the previous record was 7 years, and did K2 without O2 in winter 2021. First winter ascent of K2 was by a 10 sherpa team. Check npr.org/sections/goatsandsoda/2017/05/28/530204187/… and pubmed.ncbi.nlm.nih.gov/2334108
    – ahron
    Commented Jan 20, 2022 at 10:31

I've read most of the papers and I think the conclusion is that there are too many factors to control for (the cold, individual anatomy, age, fitness, previous HA exposure, metres reached, etc.)

If you disregard the Fayed paper as an anomaly and the only one that wasn't a prospective cohort study, it seems that the evidence generally points towards:

  • 7000m and 8000m peaks seem to present some kind of neurological finding in 10-15% of climbers

  • SpO2 is probably a reasonable proxy for the probability of this (anything sub-70% seems to correlate with higher probability). Lake Louise AMS scores less so.

  • 6000m+ seems in most papers (I think the Kottke one is probably the best) to impact white matter fraction but it's unclear whether this is permanent or means much.

  • The consensus from a couple of papers is that 'motor function' seems to be most affected, reflected in things like finger tapping exercise scores.

Proper acclimatisation, avoiding camps above 7000m if remotely possible (not going to be on most 8000ers), and avoiding SpO2 dropping below 70% seem to be the most obvious recommendations.

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