So synonymous is the Sherpa with climbing expeditions to the top of the world’s highest peaks that you could be forgiven for assuming the word refers to a job description – a Nepalese high-altitude mountain guide – rather than, in fact, a member of an unique ethnic group.
What makes the Sherpa people, who have lived in the Himalayan mountains for thousands of years, so well-adapted to the high-altitude life, able to function on levels of oxygen that mean incapacity or even death for others, has inspired plenty of investigation. Past studies point to Sherpas having fewer red blood cells but higher levels of nitric oxide, which open up blood vessels and keep blood flowing.
It turns out, though, that the Sherpas’ genetic adaptation to a low-oxygen environment isn’t just in the blood but also the muscles. In fact, it has to do with their whole metabolism.
The finding comes from research by a team led by scientists from the University of Cambridge who, to better understand the biological differences between the Sherpas and “lowlanders” monitored two separate groups (one comprising Sherpas, the other lowlanders) as they made a gradual ascent up to Everest Base Camp, 5,300 metres above sea level. For most people hypobaric hypoxia (insufficient supply of oxygen due to low air pressure) begins to set in at about 3,000 metres. The peak of Everest is 8,848 metres, with the part above 8,000 metres known as “the death zone”.
Using parallel molecular, biochemical, physiological and genetic approaches to study the difference between the groups, the researchers report that Sherpas demonstrated a lower capacity for fatty acid oxidation in skeletal muscles, along with more efficient use of oxygen, improved muscle energetics, and protection against oxidative stress.
At a mitochondrial level – which is to say, at the level of power generation within cells – the Sherpas used oxygen more efficiently to produce the energy required to power their bodies.
As well as converting oxygen and nutrients more efficiently into adenosine triphosphate (ATP, the principal chemical powering the body), Sherpas also showed higher levels of phosphocreatine, an energy reserve that acts as a buffer to help muscles contract in the absence of ATP. After two months at high altitude, phosphocreatine levels crashed in the lowlanders but increased in the Sherpas.
These metabolic adaptations, the researchers write in Proceedings of the National Academy of Sciences (PNAS), appear to be related to an enriched gene known as the peroxisome proliferator-activated receptor A (PPARA).
The study was part of Xtreme Everest, a project that aims to improve outcomes for people who become critically ill by understanding how our bodies respond to the extreme altitude on the world’s highest mountain. This year marks 10 years since the group’s first expedition to Everest.
The researchers note that the Sherpas’ adaptations provide an advantage even in the womb, since “fetal growth at altitude [is] poorer in Lowlander populations than in many native highlanders, including Tibetans and Sherpas”.