Brussels, 19 Feb 2004
Tibetans who live at over 3,500 metres above sea level have, at least in part, inherited a system of protection against the effects of lack of oxygen on their muscle tissue, according to new research.
Oxygen deficiency, or hypoxia, not only affects the lungs and brains of mountain climbers in the form of altitude sickness, but also affects their muscles. Research carried out with members of two Swiss Everest expeditions in the 1980s revealed that the number of mitochondria, the 'powerhouses' of cells, declined in European climbers exposed to hypoxia, resulting in cell damage in muscle tissue. This is because hypoxia leads to the formation of free radicals, highly reactive atoms or molecules, which attack the mitochondria.
Amazingly, however, the indigenous Tibetan Sherpas were immune to such muscle damage. This led scientists to question whether their bodies had adapted to hypoxia during the course of their lives, or whether they have become genetically adapted to the extreme conditions after 15,000 years of colonisation of the Tibetan plateau by their ancestors.
In order to try and find an answer, a joint Swiss-Italian team of researchers, led by Professor Hans Hoppeler from the University of Bern, carried out a comparative study with nine Tibetans residing at altitudes above 3,500 metres, six Tibetans whose parents had emigrated to the lowlands (at approximately 1,500 metres), and a control group of nine Nepalese, also residing at 1,500 metres.
The results clearly showed that Tibetans have significantly higher levels of an antioxidant enzyme known as glutathione S-transferase, which neutralises free radicals in muscle tissues, compared with the Nepalese volunteers. Those Tibetans living at altitude had levels around 380 per cent higher than the control group, while the lowland Tibetans had up to 50 per cent more of these enzymes.
'Thanks to this enzyme the Tibetans are presumably better equipped to neutralise the free radicals produced as a result of hypoxia,' said Professor Hoppeler. 'It is the results from the Tibetans who live in the lowlands that prove the hereditary adaptation to life at high altitudes. If the phenomenon was purely environmentally induced, these individuals should have shown no difference from the control group,' he told CORDIS News.
Aside from making an important discovery about the human body's ability to adapt to extreme and inhospitable environments, the research results will have more practical applications, Professor Hoppeler explained. 'These results add weight to the argument that altitude is basically not good for you. Athletes and climbers will need to limit their high altitude exposure to the absolute minimum needed to achieve a defined level of adaptation,' he concluded.