The study shows that among 2,211 climbers during the spring seasons from 1990 through 2005, the overall chances of reaching Everest's summit were nearly 31 percent, but they dropped to 13 percent for climbers in their 60s. The overall chances of dying on the mountain were 1.5 percent, but they more than tripled to 5 percent for climbers 60 and older.
The researchers did not find any gender differences.
"Before we did this analysis, we didn't know whether age would be important. Younger climbers have a physical advantage but probably have less experience than older climbers," said Raymond Huey, a University of Washington biology professor. "We used to refer to this advantage of age as the Kareem Abdul-Jabbar effect. As he got older, his physical skills declined but he was so smart and experienced that he was able to compensate and still play professional basketball at the highest levels.
"Unfortunately for older climbers, that effect does not apply on the world's highest mountain," said Huey, lead author of a paper describing the research published online Aug. 15 in the Royal Society journal Biology Letters. The Royal Society is the United Kingdom's national science academy.
Other authors are Richard Salisbury, a database analyst and mountaineering historian in Ann Arbor, Mich., and statisticians Jane-Ling Wang and Meng Mao at the University of California, Davis.
The findings run counter to the notion published in a medical journal in 2000 that people in their 60s could safely climb peaks of about 26,300 feet. Mount Everest is about 29,030 feet.
"I think they were overstating the safety factor. I think it's much more risky," Huey said.
Huey suspects there are two possible reasons why fewer climbers older than 40 reach the summit and successfully make it down again – declining physical capacities and a higher degree of caution that causes them to stop short of their goal of reaching the summit.
"By the time you are 50 or 60, you've probably been banged up once or twice. You know it hurts, and you've seen consequences of losing fingers or toes to frostbite," Huey said. "So older climbers are probably more cautious, but I can't determine whether it's greater caution, reduced fitness or a combination of the two that explains the lower success rate for older climbers."
The research, funded by the National Science Foundation, consisted of a statistical analysis of climbers since 1990, looking at the influence of age and gender on success and death rates. Much of the data come from Elizabeth Hawley, who chronicled climbing expeditions in the Himalayas and for four decades conducted interviews that provided a large historical archive of mountaineering information.
The analysis found virtually no difference between men and women on Everest – there are many fewer women climbers, but their rates of reaching the summit and of dying are very similar to those for men.
But age differences were stark. Those at least 60 years old who started up the mountain had a death rate at least three times higher than younger climbers. For those who actually reached the summit, 25 percent died before completing the descent, compared with 2.2 percent for younger climbers. However, because the sample of older climbers is relatively small, the actual difference could be exaggerated or understated, Huey said.
Many more people in general are trying to climb Everest than, say, 30 years ago – there are reports that just this spring more than 600 people reached the summit. The first two climbers to scale Everest, Edmund Hillary and Tenzing Norgay, were 33 and 39 when they succeeded in 1953. For many years, only about 20 percent of the climbers were older than 40, and those older than 60 were very rare. But the scientists found that in recent years nearly half of all climbers are at least 40, and one of every 30 is at least 60 years old. Until now, these older climbers had no way of knowing about how age correlates with their chances of success and death.
Huey believes it is likely more older climbers are now attempting to climb Everest because guided expeditions are readily available and because many older climbers have sufficient disposable income to pay for those guided trips.
"Older people are usually healthier now than they were 50 years ago," he said. "Many fewer people smoke and health care is better, so increasingly older people are participating in a variety of sports."
But, as the researchers concluded in their paper, "On Everest, youth and vigor trump age and experience."
Vince Stricherz | EurekAlert!
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