Scaling great heights

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Anthropology / Evolution / Genetics / Health / Myths

Sherpas – sometimes called superhumans – are extraordinary mountaineers who are at home in the peaks of the Himalayas. What is it about Sherpas that enables them to power on at such high altitude?

Sherpas perform extraordinary feats of endurance at high altitude. Image credit: Niklassletteland via Wikimedia Commons

The top of the world

Standing at 8,848 m above sea level, the peak of Mt. Everest is not a welcoming place for humans. We need oxygen, and up there, oxygen levels are only a third of those found at sea level. Some people begin to experience mild altitude sickness, including headaches, nausea, dizziness and exhaustion, at only 2500 m above sea level. Climbers who venture above 8000 m have entered the ‘death zone’: our bodies, particularly our brains, don’t do well without oxygen.

The way to help our bodies cope with high altitude is to allow them to adjust gradually. Climbers spend many weeks acclimatising to high-altitude conditions, slowly moving higher into the mountains. Research has shown our bodies are reasonably good at adjusting to low-oxygen conditions: spending just two weeks in the mountains cause changes in our blood that may last for months. But fewer than 200 climbers have ever managed to reach the summit of Mt. Everest without supplemental oxygen.

One group of people famous for their ability to thrive in low-oxygen conditions are the Sherpas. Sherpas are an ethnic group from Nepal who have lived in the high altitudes of the Himalayas for generations.

Superhumans

Behind virtually every successful summit of Mt. Everest by foreigners, there are climbing Sherpas. We’ve all heard of Tenzing Norgay, famous for having been the first, along with Sir Edmund Hillary, to reach the top of Mt. Everest in 1953. While Sherpas have been called the forgotten heroes of the mountain, you’re sure to be familiar with their incredible climbing abilities. Sherpas hold the world records for reaching the summit of Mt. Everest the fastest and the most times, and Sherpas who act as guides and porters for foreigners who climb Himalayan peaks.

Researchers have long wondered how Sherpas live and work at altitudes that make the rest of us sick. Scientists have put together pieces of the puzzle over the last few decades, studying Sherpa genetics and the evolutionary history of Himalayan people. We know the Sherpa people have been living at high altitude for centuries and have many evolutionary adaptations to low-oxygen conditions.

One normal response our bodies have to low levels of oxygen is to produce more red blood cells. This is a great way for our blood to carry more oxygen, but it also means our blood gets thicker and is more likely to clog blood vessels. Past research has shown Sherpas actually have fewer red blood cells, but higher levels of nitric oxide, a chemical that opens up blood vessels. But research published this month has given us new insights into Sherpa physiology, and the trick to their high-altitude living is not just in their blood.

Extreme science

In 2013, an Xtreme Everest science expedition headed to Everest Base Camp, located at 5,300 m above sea level. The researchers wanted to learn more about human biology at high altitude and took 180 volunteers with them. Sixty-four were Sherpas, the rest, members of the public who live at low altitudes (‘lowlanders’). The scientists looked at the blood, bones and muscle of each member of the two groups before and after they had reached base camp.

It turns out Sherpas can conserve muscle energy at high altitude because of the way their mitochondria function. Mitochondria are like batteries, the energy centres in each of our cells. The research showed the Sherpas’ mitochondria use oxygen much more efficiently then the lowlanders when producing the energy their bodies need. And while the energy reserves in the muscles of the lowlanders decreased the longer these people spent at basecamp, energy reserves increased in the Sherpas’ muscles, despite the low oxygen.

Sherpas have spent thousands of years living at high altitudes, so it should be unsurprising that they have adapted to become more efficient at using oxygen and generating energy.  Dr Andrew Murray, University of Cambridge

This research isn’t just about helping gung-ho adventurers survive the slopes of Everest. Many critically-ill patients also experience a fall in oxygen levels, for example when suffering heart failure, lung diseases and many cancers. Understanding the way Sherpa physiology has evolved to cope with extreme conditions may just help all of us one day.

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