Is there evidence to support or refute the hypothesis that frequent trips to high altitude aid acclimatization?

Question

Many years ago, I was reading a book in which the Chamonix guides of the 1940s and 1950s were featured. It could have possibly been Annapurna by Maurice Herzog, but I just don't remember.

Several sentences in the book implied that an older climber — one who made repeated trips to altitude over a period of years — acclimatized quicker on subsequent trips than younger, relative newcomers to altitude. (I remember the term "older climber".) This was a personal observation, and was not expanded upon. But this was probably written in the 1950s, and the mechanisms of acclimatization have received much scrutiny since then.

Is there any evidence to refute or support this hypothesis?

I can think of several possible explanations for this observation:

1. It is true that repeated trips to high elevation change the physiology of the climber to make acclimatization easier, quicker, more complete.

2. Climbers who repeatedly go to altitude develop conscious and unconscious habits that aid acclimatization (e.g., religiously staying hydrated when possible, getting enough sleep, avoiding alcohol, knowing when to retreat to refresh themselves, when to stop and when to continue.)

3. Climbers who repeatedly go to altitude grow accustomed to the discomfort of acclimatization and ignore the discomforts.

4. None of the above. The statement flatters older climbers.

And other explanations are also possible, including the fact that even if the hypothesis is true for Alpine altitudes, no European mountain approaches the high Andes or Himalayan altitudes.

Background: Note by older, the author (whoever he was) probably meant climbers in their 30s or so, not really old climbers. At the time of the Annapurna expedition (1950), Louis Lachenal was 29, as was Lionel Terray and Gaston Rebuffat. Maurice Herzog was 31. On a modern note, Ed Viesturs climbed his 14th 8,000er, Annapurna, at 46, without supplemental oxygen.

Answer 1

There's quite a bit of evidence that populations that live at high altitude (e.g. Sherpa in Nepal) have evolved some physiological changes that allow them to function at high altitude as a non-high altitude adapted person would at sea-level. See this review for one example, but there are many other similar papers and studies.

I've been struggling to find primary sources until I found this review (secondary source obviously), which has a section labeled Epidemiology with a number of primary sources for those interested.

First off, lets look at the incidence of High Altitude Pulmonary Edema (HAPE) in a general population. HAPE is a dangerous condition that can lead to death if not promptly treated. Basically it is a swelling of the lung that can't be reduced without return to lower levels.

According to Hochstrasser et al. (1986), the prevalence of HAPE in a general mountaineering population in Alps is <0.2% (Hochstrasser et al., 1986). Among trekkers in the Himalayas (Maggiorini et al., 1990) and climbers in the Alps (Hackett and Rennie, 1979) ascending at a rate >600 m/day HAPE incidence is around 4%. The risk of HAPE rises with increased altitude and faster ascent. The incidence among persons with an unknown history of high-altitude pulmonary edema is 0.2% if they ascend to 4500 m in 4 days and 2% if they ascend to 5500 m in 7 days. The incidence increases to 6% and 15%, respectively, when these altitudes are reached within 1–2 days (Bärtsch and Swenson, 2013).

So, it looks like between 0.2% and ~15% depending on the study and, how high, how fast they ascended, and degree of susceptibility.

Now lets look at the incidence in those who have previously had HAPE or similar conditions:

Climbers with a previous history of HAPE, who ascend rapidly above 4500 m, have a 60% chance of HAPE recurrence (Bärtsch et al., 2002). Susceptible individuals can avoid HAPE if they ascend slowly with an average gain of altitude not exceeding 300–350 m/day above an altitude of 2500 m (Bärtsch et al., 2003). When an altitude of 4559 m is reached within 22 h, the HAPE incidence increases to 7% in mountaineers without, and to 62% in those with a history of radiographically documented pulmonary edema (Bärtsch et al., 2002). Susceptibility to HAPE may increase in mountaineers with unrecognized underlying illness; some individuals may have developed diastolic heart failure rather than HAPE, which was due to hypertensive heart disease (Bärtsch et al., 2003).

So, ~60% of those who have had it before, will get it again, if they ascend too fast, and that if you have had it before you are much more likely (4x) to get it again.

This implies that the process is simple weeding out - those who are not fit for altitude tend to get sick and don't want to risk it again. I couldn't find any evidence that says that repeated visits to altitude result in faster acclimatization, only that the same processes occur with each visit.

Note that climbers today are fitter (exercise plans and all) and have better (lighter, tougher, warmer) gear than those of even 20 years ago, let alone 50 or more years ago. We also have a much greater understanding of the physiology of altitude sicknesses and adaption, so the science can be applied to climbing and climbers, resulting in a pushing of boundaries and extra-ordinary feats like those of Viesturs et al.

Answer 2

Anecdotally I can tell you in my 20s I was exposed to high altitude 7K feet plus "regularly, maybe two or three times a year. I never suffered any altitude sickness or experienced any shortness of breath. Fast forward to late 30s and beyond I haven't visited high altitude places much and was recently at 10Kfeet altitude and definitely felt it. I don't know if it's purely age and/or age + exposure. I suspect the latter.