Different Patterns of Altitude Adaptation

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It's well known among endurance athletes and mountain climbers that the low oxygen concentrations at high altitudes can cause extreme distress. It's also well known that by spending significant amounts of time at altitude, you can acclimate substantially--mostly by increasing your red blood cell count. This effect is used by climbers to work their way up gradually to higher altitudes and by endurance athletes in an attempt to improve their performance at low altitudes (see altitude training). As it happens, there are a number of populations who live normally at very high altitudes. What about them?

It turns out that there are three major areas where humans have been living at high altitude (~ 4000 m) for long enough to show an evolutionary adaptive response: the Andes, the Tibetan Plateau, and the Ethiopian Highlands. Each such population appears to have some adaptation, but what's really interesting is that the adaptations seem to be different:

  • Andeans appear to have adapted more or less the same way that your average person of European ancestry would: they have higher red blood cell counts. This to some extent ameliorates the effect of altitude, but they end up with lower oxygen saturation (how much of the hemoglobin is carrying oxygen) at high altitudes, but because of their high hemoglobin concentration, they actually have higher total blood oxygen levels than normal sea level values.
  • Tibetans have a much weaker response in terms of hemoglobin concentration and also experience lower oxygen saturation (about 10% below normal values). They appear to have exhibited some selection toward higher saturation values. I'm actually finding this a big puzzling since it almost seems like they've adapted to live with lower oxygen delivery. I'm not clear how that works. I could be misreading the literature here, though.
  • The Ethiopian case is the most interesting. Beall's data indicates that at ~3530, Ethiopians have normal looking hemoglobin concentrations but also oxygen saturations nearly as good as those seen at sea level, as seen in the figure below.

Figure from Beall 2002. [this used to read "after Beall". corrected 2006-05-02, EKR]

Unfortunately, we don't yet know biochemically how these adaptations work. It would be particularly interesting to understand the nature of the Ethiopian adaptation, which seems like it might involve better oxygen transport into the blood rather than better oxygen carrying capacity in the blood. That's potentially a useful adaptation even at low altitude.

A lot of the interesting work in this field seems to be being done by Cynthia Beall at Case Western. This post is mostly based on her fascinating review in Integrative and Comparative Biology (behind pay wall, abstract here). She also has an extensive interview here which I haven't had a chance to listen to yet.


Very cool...

Related things I'd like to know...

Implication for aerobic sports? I seem to recall fun stuff about US Olympic team and Mexico city.

Why does alcohol seem to have more effect (per volume) at higher altitudes.

It seems plane pressurize to simulate about 14,000 feet. Is this true? Why that altitude. Why not over the plan flight linearly move from pressure as departure airport to the pressure at destination airport.

Implications for aerobic sports: It's widely believed that people who live at high altitudes will have superior performance at low altitudes. The converse is certainly true: if you live and train at low altitudes, you will have lousy performance at high altitudes.

Airplanes are pressurized to simulate below 8000 feet--most people experience discomfort at 14k, o that would be too high. My understanding is that it's expensive to pressurize to sea level, so 8k is a compromise. This also explains why not move linearly from departure to arrival: very few destinations are anywhere near 8k feet.

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