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Bundled up in heavy clothing, his face and eyes protected from the fierce Andean sun, Otilio Huanca moves slowly across the bone-dry earth of the Arasi gold mine in Peru, breathing deeply and directing bulldozers as they claw great chunks of rock out of the barren mountain side.

At 5,000 metres above sea level — higher than any mountain in western Europe — this is one of the most inhospitable places on earth to work. The light is blinding, the temperatures plummet at night, the mine is sometimes whipped by snowstorms and the air is thin on oxygen. “It’s a challenge,” acknowledges Huanca, pulling aside the face mask that protects him from the dust. “It can be hot one minute and cold the next, and above all it’s difficult to breathe.”

Huanca is one of around 150m people worldwide who live and work at high altitude, generally defined by medics as at 2,500m and above. From the Tibetan plateau to the Ethiopian highlands, miners, farmers, shepherds and factory workers are toiling in conditions that can sometimes be detrimental to their health.

Nowhere is this truer than the Andes, home to three of the highest capital cities on earth — Colombia’s Bogotá, Ecuador’s Quito and Bolivia’s de facto capital La Paz which, at over 3,600m, is the highest of them all.

Some Andeans spend their lives at altitude. Others, such as miners in parts of Peru and Chile, make dizzying journeys from lowland camps to high mountains in a matter of hours to work strenuous shifts in oxygen-thin air.

Otilio Huanca, who works at the Arasi gold mine in the Peruvian Andes

Whereas in the past people tended to live and work close to where they were born, immigration in a globalised world means more people than before are exposed to the impact of working in environments to which their bodies are not accustomed.

Keeping these people healthy is a challenge for companies, public policymakers and physiologists, who are still trying to understand the long-term implications of working in the mountains or of changing altitude abruptly.

José Luis Recoba, a doctor at the Arasi mine, says that when new workers arrive on site, the first 10 days are critical. Their breathing rate and heart rate increase as the body tries to compensate for the lack of oxygen in the air. They often suffer headaches, nausea and a loss of appetite, classic symptoms of what the Andeans call soroche, or mountain sickness.

After about 10 days the body produces extra red blood cells that help carry oxygen round the body. That helps with breathing but also means the blood is thicker and clots more easily, increasing the chances of a pulmonary or a cerebral oedema.

“If your body responds properly, you don’t need to worry, but if it doesn’t you really have to go down, otherwise you could die,” Recoba says.

Workers at high altitude can suffer from mountain sickness

While plenty of research has been done on the impact of living and working constantly at high altitude, less is known about the effects of changing altitude quickly, an increasing trend in places such as northern Chile, where miners sometimes work intensive shifts at altitude but spend down time at sea level.

“This is a relatively new phenomenon,” says Julio Brito, director of the Institute of Health Studies at Arturo Prat University in Iquique, Chile, and one of the authors of a recent study on the subject. “It’s a new way of working.”

Brito and his colleagues examined 120 Chilean miners who worked seven-day shifts at over 4,000m and then descended to sea level for seven days. They found that even though the men were used to working at altitude, many of them suffered soroche each time they went back up the mountain. The study also found that the miners were more prone to mild pulmonary hypertension — high blood pressure in the blood vessels that supply the lungs, a serious condition that can damage the right side of the heart — than low-altitude workers and the that walls of their hearts were thicker. “The heart has to work harder at altitude and, like any muscle that works hard, it grows,” Brito says. “What we don’t know yet is what the long-term health implications are of this kind of intensive shift work.”

Peru’s Arasi gold mine, one of the toughest places to work on earth

Companies are having to take these new findings on board. At Chile’s gigantic Escondida copper mine, majority-owned by Anglo-Australian multinational BHP, doctor Jaime Piña and 100 other health professionals are responsible for the wellbeing of nearly 11,000 direct and indirect employees, most of whom work at over 3,000 metres.

The company has eight clinics on site to deal with medical problems and three gymnasiums to encourage the miners to stay fit. Dormitories are equipped with humidifiers and blackout curtains to help workers sleep well — often a challenge at altitude. The food in the canteen encourages healthy eating and, above all, workers are subjected to regular medical exams. “No one — and I mean no one, not even the chief executive — is allowed on site without a medical check-up which confirms they are fit to work at over 3,000m,” says Piña.

As a result of all these preventive measures, Piña says that even though they are labouring in the Andes, workers at Escondida are far less likely to suffer cardiovascular problems than people living and working at sea level. However, like Brito, he says there is still much research to be done on the long-term impact of working at altitude.

A study, conducted in Tibet and China and published in Nature magazine in 2015, reported that “sustained exposure to high altitude leads to cognitive decrement, such as impairment in attention, memory, judgment, and emotion”.

The indigenous people of the Andes say they have had at least a partial solution to highland labour for thousands of years: coca leaves. Chewing them releases an alkaloid that numbs the senses and allows workers to endure hard graft.

When the Spanish arrived in the Andes in the 16th century, they outlawed the chewing of coca, regarding it as a diabolical pagan habit. They soon changed their minds when they saw the impact the ban had on indigenous miners, whose productivity slumped.

Within a few years the Spaniards overturned their ban and came up with an altogether more profitable coca policy: they taxed it.

Scientific research has made the case for coca. “Chewing coca leaves induces biochemical changes that enhance physical performance at high altitude,” concluded one study published in 2010 in the Indian Journal of Biochemistry. “These changes appeared sustained,” the authors of the study noted, adding that mine workers were the largest consumers, chewing 13 oz (370g) a week.

A miner in Bolivia chews coca leaves © Getty

Jorge Hurtado, a Bolivian psychologist and author of books on coca use in the Andes, says chewing the leaves or drinking coca tea can help prevent blood clots. He compares coca use in the Andes to coffee consumption elsewhere. “Coffee sharpens the mind, while coca helps with endurance,” he says.

“It’s impossible to imagine this part of the world without coca, it’s used by so many ordinary people, just to get them through the working day, particularly if they do strenuous work or work at altitude.”

While coca cultivation is almost entirely outlawed in Colombia, where it is used primarily to produce cocaine, the Bolivian government allows some farmers to grow it and has no plans to ban its use.

“It would be like banning coffee on Wall Street,” Hurtado says. “Can you imagine the impact of that?”

How to stay healthy at high altitude

• Ascend gradually. Some doctors recommend climbing only 500m or 1,000m a day to allow the body to acclimatise.

• Consider taking acetazolamide, a medicine that fools the body into making you breathe more deeply. As with all medicines, be aware of potential side-effects and read the instructions carefully.

• Rest on arrival. Walk slowly and don’t try to do too much on your first day.

• Drink lots of water as high altitudes are dehydrating. Avoid coffee and alcohol.

• Eat iron-rich foods such as red meat and spinach to increase your red blood cell count. Be careful though — after a while your body will do this naturally.

• If you are in the Andes, drink coca tea. It can alleviate headaches and nausea triggered by altitude.

• If you get mountain sickness and it persists, move to lower ground.

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