On May 23, 2007, Professor Mike Grocott and his team of climbers – eight medical researchers, two cameramen shooting a documentary and 15 Sherpas carrying equipment or guiding the climb – were 300 metres from the summit of Mount Everest when they hit a big problem.

Just ahead of them, a man from another party was in trouble, staggering around and gasping for air. His body had became hypoxic and his oxygen-starved brain began to swell. His team buzzed their doctor at a camp below on a two-way radio, who reassured them that he would be OK.

Grocott, an expert in high-altitude sickness, had a different opinion: it was clear to him that the man was dying. “It often happens,” says Grocott. “If you’re a doctor on a mountain, you expect to be called on to help people.”

As the light began to fade and the temperature dropped, the man’s condition worsened. Vijay Ahuja, a medical student in Grocott’s team, insisted they get involved. The stricken man’s colleagues conceded there was a problem, but it was now too dark to take him down to safety. Recognising the seriousness of the situation, one of the doctors on Grocott’s team, Dan Martin, began treatment. Martin worked through the night, managing to keep the seriously ill climber alive until dawn, when the patient’s team were able to transport him down the mountain.


In the morning, Grocott, readying his climbers for a final ascent, watched another stranger – this time returning from the summit – collapse on the icy slopes. They helped rescue him, too. “People with altitude sickness like that often assume they’re just feeling rough, and it’s not the lack of oxygen causing the trouble. They think things like, ‘It’ll all be OK if I can just get over that pass’, because they lose insight and act irrationally,” Grocott says. “The question, to me, is why are some people affected like that while others aren’t?”

On the mountain, Grocott and many of his team were feeling “drunk” and exhausted from the thinness of the air, and even with bottled oxygen piped into their breathing masks they needed to take about 15 deep breaths per step. The Sherpas accompanying them on the climb, however, were breathing easily. “To see them at altitude was amazing,” Grocott says. “They do the whole thing without needing any extra oxygen, whereas lowlanders like us struggle to survive without it, even if we’ve acclimatised. We couldn’t have done that expedition, nor a lot of the work that came after, without them.”

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They reached the summit later that morning. The temperature was approximately -25°C and the wind reached 20 knots. The researchers wanted to take blood samples from them at the peak, but were driven to retreat by the conditions. They descended 400 metres and took blood there. Their samples remain the least oxygenated human blood ever collected in healthy humans – comparable to that observed in people suffering cardiac arrest or after an opiate overdose.

In fact, according to science, the climbers should have been dead.


Professor Mike Grocott, chair of Xtreme Everest Jay Brooks

Lean, affable and dressed in a check shirt and khakis, Grocott, 52, has the air of an ex-rugby pro who can organise desk-bound staff, but is at his happiest outdoors. He has two day jobs: professor of anaesthesia and critical care medicine (the term is interchangeable with “intensive care unit”, or ICU) at the University of Southampton, and consultant in critical care medicine at the city’s University Hospital. His own office at the Hospital would be nondescript if it were not for the Himalayan maps and framed photographs of Sherpas.

Grocott is also head of the Xtreme Everest organisation, which researches the effects of high altitude on the human body. This team of doctors and scientists has constructed the world’s highest makeshift science lab in order to test their performance in the most oxygen-starved location on Earth. To the layman this may seem an obscure interest, but in fact it has relevance to the way we treat the very sick in intensive care.

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Regardless of the specific medical condition, getting oxygen to the body’s cells, where it facilitates the conversion of food to energy, is the fundamental problem for the vast majority of patients ill enough to be in intensive care. Too little oxygen reaching vital organs is the main cause of death in ICUs, so people whose bodies use it efficiently tend to survive, while the inefficient – around 25 per cent of all patients – do not. The same problem affects lowland mountaineers: some are relatively unaffected by the thin air, whereas others suffer swelling of the brains or lungs, which can be fatal.


Health and fitness have no bearing on human oxygen efficiency: Xtreme Everest has taken 70-year-old civilians up the mountain with no problems, but fit, young military personnel have had to turn back. The issue is genetic, and for the last ten years Xtreme Everest has been trying to identify the specific genes concerned, which in turn might allow scientists to develop drugs that would mimic oxygen-efficient physiology. About 325,000 people are treated in ICUs in the UK each year, and Britons have a one in five chance of ending up in one at some point. Around 80,000 British people die from oxygen-related problems in ICUs every year.

Grocott has been climbing since 1975 when, as a nine-year-old growing up in Manchester, he saw Chris Bonington talking about climbing Everest’s south-west face on children’s TV show Blue Peter. As a doctor, most of his career has been spent working in intensive care which, he says, has a lot in common with mountaineering: both are about “carefully considering risk, applying judgement and carefully laying out and completing courses of action”; and they appeal to him because he dislikes risk so much that he enjoys minimising it.

Using mountains as a means to explore medical conditions has seemed natural to him since the day in his twenties, climbing Aconcagua in Argentina, he saw a trainee anaesthetist friend diagnose a high-altitude cerebral edema in a fellow climber, and lead him down to safety. “At that moment, I really understood that the physiology of how the body works at high altitude is the same as when they’re in critical care,” he says. “So extreme environments give you a window on what extreme versions of physiology look like.” On mountains, he had seen hypoxia (low oxygen levels) acting on otherwise healthy bodies, so its effects could be clearly observed. Was there a way, he wondered, of using the mountain experience to learn about the effects of hypoxia while in the lowlands?

In 1999, Grocott and a colleague, Kevin Fong, set up the Centre for Altitude, Space and Extreme Environment Medicine (CASE) under the auspices of University College Hospital in London. Fong, who had studied astrophysics before medicine, was interested in how the body worked in space.

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Xtreme Everest's research discovered that Sherpas use oxygen more efficiently than lowlanders Steve Brown

A crucial belief among CASE members was that differing reactions on the mountains demonstrated that the decisive factor in patient survival was not the amount of oxygen available, but the way the individual bodies reacted. This was radical. For years it had been widely accepted that hypoxic patients could be helped by pumping them full of oxygen, but many doctors had seen some patients react against excessive amounts.

It was clear that people processed oxygen differently. The CASE scientists wanted to run tests on a large sample of hypoxic people to compare their reactions. The question was how? On the wards there were the complicating factors of the original illness – and anyway, patients tend to dislike being researched in near-death situations. That left the option of putting healthy people in a hyperbaric (pressurised) chamber – a large and expensive piece of equipment to hire.

In the early 2000s CASE’s informal conversations turned speculatively to a scientific expedition on Mount Everest. It sounded crazy at first, but the more they talked, the more it made sense. Base Camp on the Nepalese side of Everest is high enough (over 5,000 metres) to have a substantial drop in oxygen levels, but approached from the south it can be reached by walking. Because a lot of people want to climb part of Everest it would be reasonably easy to recruit a large sample – say 200 people – who would pay for their own travel and give their time for free. And the Everest name would attract sponsors who would help with the costs of hauling heavy, expensive lab equipment up a mountain.

Serious planning began in 2004. The team organised expeditions to other mountains and systematically tested the equipment. For several months, they hired a butcher’s refrigerated van, testing gadgetry at low temperatures. Spinning hard drives don’t work in thin, cold atmospheres, so they used Panasonic Toughbooks with the drives replaced by high-end SD cards running stripped-down versions of Windows. Sponsors, including Phones 4U co-founder John Caudwell – after whom the project is named – covered the £2.5 million cost. Sixty scientists, medics and researchers were recruited; 198 members of the public would trek to Base Camp, making themselves hypoxic in the process, and be tested. There would be 60-odd tests on most members of the party, with 15 climbing on to the 8,850-metre-high summit, where they would set up a lab and take the highest-altitude, lowest-oxygen blood samples in history. The simple aim: to discover the key difference between the bodies of the people who coped with the drop in oxygen and those who did not.

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Not everyone was convinced of the project’s merits. Ned Gilbert-Kawai, a trainee anaesthetist and intensive-care doctor who joined the organisation in 2008, and who planned the research programme for a 2013 trek, says that “for that first expedition there were lots of critics who thought it was an excuse to climb mountains. Others said it was not a valid approach because they were testing the fit and healthy rather than people who were unwell.” The comments were mostly made at conferences, Grocott says. “You’d get asked about it, or people would just say, ‘Why don’t you just use a hyperbaric chamber?’” He wasn’t worried by the criticism. “I guess we were quite a young team at the time and we were quite unheard of, so it was reasonable to ask if it wasn’t an uneconomic way of doing the research. It’s an understandable opinion. But it’s also wrong. The answer is that it would be far more expensive in a hyperbaric chamber. ”

At the start of 2007, the logistics team air-freighted 150,000 items, weighing a combined 27 tonnes, from the UK to Kathmandu. Some of the equipment was used for labs in Kathmandu and the Sherpa capital Namche Bazaar so that the trekkers – whose route passed through both places – could be tested at the lower levels of the ascent. The rest was transported by helicopters, Sherpa porters and yaks to the 5,300-metre-high Base Camp.

Base Camp itself is an uneven rock-strewn plateau 600 metres above Namche Bazaar. Ringed by snowy Himalayan peaks, it’s covered in jarring, primary-coloured tents pitched by the tens of thousands of climbers who pass through each year. In the middle of this strange settlement, the Xtreme Everest crew set about building not just a lab, but a mini town of 97 tents, powered by 38 Honda diesel generators. Most consisted of basic accommodation, but there was also a field hospital, dining facilities, kitchen, communications centre and a workshop.

The lab consisted of seven green, double-thickness US military tents, each around two and a half metres tall, their interiors fully lined and carpeted for insulation and lit by bare electric bulbs. Outside, with the Sun’s daytime glare intensified by the stark white snow and ice, coloured bunting tied between them lent an almost festive air to the complex; inside, however, they were crowded and purposeful. Desks crammed with laptops and medical kit were set up around the edges, with chairs at the centre for people to sit on while they were examined, poked and jabbed. Nearby, exercise bikes were used to help push the volunteers’ bodies to the limit; suspended from the ceilings were odd loops of wires and tubes waiting to be connected to subjects as they pounded the bikes. Between tests, medics and subjects wandered around, occasionally having snowball fights or playing football in the thin air tinged with generator smoke and yak-dung fires.

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Between March and June, 208 volunteers climbed the rocky paths in packs of 20 or so to be tested at Base Camp. At that altitude, oxygen was 53 per cent that of sea level, and when volunteers looked at the syringes containing their blood samples, they noticed a bluish-purple tint from the extra red blood cells their bodies were producing to compensate.

There were 60-odd tests, some performed on only a few people because they were so invasive (the tonometry test, for example, involves inserting a plastic tube about a centimetre wide up the nose, down the throat and into the stomach). In total, 17,000 samples were collected. The Xtreme Everest team has compiled the most detailed study ever made of the human body at altitude.

Base Camp for the project is sited at 5,380 metres on the south side of Everest in Nepal Giles Price

Before the expedition, the researchers’ hypothesis was that some people cope better with low oxygen levels due to differences between microcirculation (the B-road channels that deliver the blood from the motorways of the main veins and arteries) and the parts of body cells called mitochondria. When we eat, our digestive system breaks down food into molecules of sugars, amino acids, fatty acids and glycerol. Most of those molecules then enter individual cells, where they are oxidised by microscopic cell-sized organelles called mitochondria, which draw oxygen from the bloodstream.

The oxidation releases adenosine triphosphate (ATP), a molecule that stores and carries energy to the bits of the body that require it – think of mitochondria as your batteries and ATP as your energy current. Mitochondria cannot produce ATP without oxygen, which is why, when deprived of oxygen, you will black out in about two minutes, and die about two minutes later.

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The test results confirmed the hypothesis. As the samples were processed, Xtreme Everest members began to publish papers and speak at conferences, and the critics were silenced. No one could now accuse Grocott’s team of just wanting to climb mountains. However, while the findings moved understanding forward, they didn’t reveal what determined why people’s mitochondria and microcirculation work so differently. “They found lots of things that were not important, but they didn’t nail what was important regarding what allows someone to cope well at altitude,” says Gilbert-Kawai. “But it did allow us to narrow the window of what we were looking at.”

The Everest project was wound down by 2008. But, as the months passed and the team talked more about the data, Grocott and the others felt that, whereas they had advanced the understanding of oxygen efficiency in the body, there were many unanswered questions. If it was all about the mitochondria, then what was it about certain mitochondria that made the difference? It would be great, they thought, if they could study some of those effective mitochondria, knowing what they now knew.

But whose mitochondria to study?

Sherpa blood samples taken by Xtreme Everest at Base Camp Giles Price

Grocott downplays the idea that the decision to study the Sherpas, whose oxygen efficiency allowed them to ascend Everest with ease, came from a sudden epiphany. The team had discussed the possibility before 2007, but there were reservations. “We do invasive procedures, and there is the issue of consent. Would they understand what we were doing? Would we be taking advantage?” And would we be materially benefitting them? During the 2007 expedition, when Sherpas carried up lab equipment weighing several tonnes, Grocott was taken by the contrast between their imperviousness to the lack of oxygen and the struggles of the other climbers. “To see them at altitude was amazing,” he recalls. “They do the whole thing without needing extra oxygen, whereas lowlanders like us struggle to survive without it. We couldn’t have completed the expedition without them.”

After the 2007 trip, however, Xtreme Everest researchers’ relationship with the Sherpas had matured into a friendship. Crucially, Grocott had learned that Nepalese hospitals were slowly developing more critical care facilities, which meant there was a possibility that the physiological experiments he would subject the Sherpas to might one day benefit them or their children.

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In 2010, Grocott contacted the Sherpas they had worked with and explained what they were trying to do. “They got it completely,” he says. Three years later, in March 2013, they loaded

up the planes and went out to do it all again.

There are currently about 150,000 Sherpas. Their name in their own language, Sherwa, (“shar” means “east, “wa” means “people”) ties them to eastern Nepal, home of the Himalayas, and genetically they are distinct from other Nepalese groups, as well as their neighbours the Tibetans and Han Chinese. Part of their distinct genetic make-up is a superior mitochondrial function that allows them not only to climb Himalayan mountains without oxygen, but also to herd cattle, sheep, goats and yak on their slopes.

Their culture has been profoundly altered by the western passion for climbing mountains, particularly since the 90s, as a proliferation of commercial guiding agencies popularised by the Everest ascent created more (highly dangerous and often underpaid) jobs for Sherpas, and increased their profile. In 2011, Mingma Sherpa, who accompanied Grocott on the 2007 Xtreme Everest expedition, became the first South Asian person to climb the world’s 14 highest peaks, and the first person ever to climb all 14 at the first attempt.

Kay Mitchell is a member of the Xtreme Everest team and a specialist in hypoxia Jay Brooks

In a 2010 study published in Science, a team of Chinese and American researchers found that Sherpas had genes that allowed them to process oxygen with great efficiency. In 2017, population geneticist Rasmus Nielsen from the University of California, Berkeley, published a study analysing the ethnic groups from whom the Sherpas may have inherited their genetic makeup.

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For its 2013 research, Xtreme Everest took another 150 British walkers, but this time Base Camp was the only destination. Again, a logistics team built a complex of facilities and labs. Three helicopters, 100 porters and more than 250 yaks were used to haul it up the slopes between Kathmandu, Namche Bazaar and the camp up closer to the white peaks.

The biggest difference was that this time, the Sherpas were not only carrying the equipment, but being tested themselves. “It was mainly their friends and family that ended up as our recruits,” he says. “We explained it to a member of the Sherpa team who could explain it to them, and they became part of the journey. They asked really smart questions that proved to us that they understood. The muscle biopsy is the most invasive thing we do. We were nervous about doing it to them, but they were very comfortable with it.”

About 50 tests were done on the trekkers and Sherpas, including a trial of a nitrite dietary supplement that boosts oxygen efficiency. In most cases, though, the work was building on that undertaken in 2007. “We measured mitochondrial functions in the field,” says Andrew Murray, a University of Cambridge physiologist who researches mitochondrial function, and who was on the 2007 and 2013 expeditions. They took a biopsy of muscle from the top of the volunteers’ legs, and then probed the mitochondrial pathways to see how much oxygen they use. “It’s very difficult technique,” Murray says. “It’s hard enough to do in a well-stocked lab at sea level and I can’t overstate how difficult it is in a tent at the Base Camp of Everest.”

The team’s findings were published in May 2017. The Sherpas were not only using oxygen to make ATP more efficiently than lowlanders, but also while the energy levels in the muscles of lowlanders drop at altitude as oxygen becomes scarcer, the energy levels in Sherpa muscles increases. “It is an extraordinary finding,” says Murray. “They need oxygen like we do, but in that low-oxygen environment, they produce not just more energy than us lowlanders, but they themselves have more energy than they do at sea level. In other words, as they climb upwards into the environment where they have adapted for thousands of years, they become healthier.

“What excites me is that we are witnessing human evolution here,” Murray continues, “It’s happened over thousands of years, but that’s quite recent in a human time frame. And it’s associated with gains in performance.”

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There are still lots of unanswered questions about the findings. We don’t know, for instance, if the higher energy levels are purely due to oxygen efficiency, or if superior energy conservation plays a part. It could be that Sherpa bodies can shut down certain functions when required. And the biology of metabolism is highly complex; although Murray’s team at Cambridge is concentrating on the effects of one gene that they know has a role with the Sherpa’s metabolic adaptation, they know it’s likely several genes will be involved. The next step will be more testing, comparing lowlander and Sherpa physiology.

Pharma companies are now working directly with Murray to use the new learnings about the mitochondria in screening new drugs for treating hypoxia. The new understanding means they can be much clearer and more efficient in identifying what may or may not work. Secondly, the Xtreme Everest team has made major contributions to the understanding that both an excess and a lack of oxygen can be harmful. There is still some way to go in understanding the quantities that are safe for individuals, and in discovering the biochemical signals to look for when trying to gauge how much is safe, but much of Xtreme Everest’s research is currently focused on that area.

University of Cambridge physiologist Andrew Murray was part of the 2007 and 2013 Xtreme Everest expeditions Jay Brooks

Earlier in 2017, Grocott and a small Xtreme Everest party flew to Nepal to mark the tenth anniversary of their first expedition. Like other members of the group, Grocott now had small children, and he and his wife Denny, a fellow team member, trekked with them to Base Camp. On arrival they went to Kathmandu for a conference with Nepalese doctors and scientists.



But the purpose of his trip wasn’t the conference, or even Everest. From Kathmandu they travelled to Namche Bazaar for an appointment at the monastery, which serves as a community centre. Waiting for them were most of the guides from 2007, research partners from 2013, village elders and hundreds of Sherpas. Grocott and the team delivered a presentation about their 2013 study, explaining what the tests had been for and what they revealed.


First, they explained how the tests they had done on the Sherpas had measured their energy and oxygen levels. The presentation then set out how those energy and oxygen levels were compared with those of the lowlander climbers, and what that said about the way Sherpa and lowlander bodies worked. Finally, it showed how those differences explained the differences in performance.

It had been a point of honour for Grocott and his crew; no one ever seemed to thank the Sherpas after employing their services, and yet they couldn’t have done any of the work without them. “It was moving to do it, and it seemed right,” he says, pushing back from his desk and preparing to head off to a lecture. “They loved the fact that they performed better than us. Well, they knew that already. But they loved how we had now measured it.”

Richard Benson is a journalist and author based in London. He wrote about forensic anthropologist Sue Black in issue 10.17