Is There a Limit to the Human Life Span?
There may be no limit to how long humans can live, or at least no limit that anyone has found yet, contrary to a suggestion some scientists made last year, five new studies suggest.
In April, Emma Morano, the oldest known human in the world at the time, passed away at the age of 117. Supercentenarians — people older than 110 — such as Morano and Jeanne Calment of France, who died at the record-setting age of 122 in 1997, have led scientists to wonder just how long humans can live. They refer to this concept as maximum life span.
In a study published in October in the journal Nature, Jan Vijg, a molecular geneticist at the Albert Einstein College of Medicine in New York, and his colleagues concluded that humans may have reached their maximum life span. They analyzed multiple databases containing data on how long people have lived in recent decades in many countries and found that survival rates among the oldest people in most countries had not changed since about 1980. They argued that the human maximum reported age at death had apparently generally plateaued at about 115. [Extending Life: 7 Ways to Live Past 100]
However, the findings of five new studies now strongly disagree with this prior work. "I was outraged that Nature, a journal I highly respect, would publish such a travesty," said James Vaupel, a demographer at the Max Planck Odense Center on the Biodemography of Aging in Denmark. Vaupel co-founded the International Database on Longevity, one of the databases analyzed in the previous study.
Vaupel argued that the prior work relied on an outdated version of the Gerontology Research Group's database "that lacked data for many of the years they studied. Furthermore, they analyzed maximum age at death in a year, rather than the more appropriate maximum life span attained in a year — in many years, the world’s world's oldest living person was older than the oldest person who died that year," he told Live Science. "If appropriate data from the Gerontology Research Group are used, then ... there is no sign of a looming limit to human life spans."
Siegfried Hekimi, a geneticist at McGill University in Montreal, and his colleagues similarly found no evidence that maximum human life span has stopped increasing. By analyzing trends in the life spans of the longest-living individuals from the United States, the United Kingdom, France and Japan for each year since 1968, they found that both maximum and average life spans may continue to increase far into the foreseeable future.
Maarten Rozing, a gerontology researcher at the University of Copenhagen in Denmark, and his colleagues said the authors of the previous study committed errors in their statistical analyses. "We think that the claim that human life span has reached its limit should be regarded with caution," Rozing told Live Science. "Overall taken, there are very strong arguments to believe that our life span is still increasing, and, as long as our living conditions keep on improving, there is no reason to believe that this will come to a halt in the future." [7 Ways the Mind and Body Change with Age]
Similarly, in an analysis of Japanese women, who make up a growing number of centenarians, or people over 100, Joop de Beer, a demographer at the Netherlands Interdisciplinary Demographic Institute, and his colleagues suggested that the maximum human life span may increase to 125 years by 2070. "There is no reason to expect that a limit to human life span is in sight," de Beer told Live Science. He added that two kind of criticisms can be made about the prior work: "They did not apply their method correctly," and "they did not apply the correct method."
But the researchers did caution that, although the prior work might not have presented a strong argument for a limit to maximum human life span, it does not mean such a limit does not exist. "The evidence is mixed, but at present, the balance of the evidence suggests that if there is a limit, it is above 120, perhaps much above, and perhaps there is not a limit at all," Vaupel said. "Whether or not there is a looming limit is an important scientific question."
"Average human life span is clearly increasing continuously," Hekimi said. "The failure to identify a current limit to maximum human life span suggests that the increase in average life span might continue for quite a while."
Vijg defended his team's October study. "We agree with none of the arguments put forward — sometimes because they were based on a misunderstanding, sometimes because they were plain wrong, and sometimes because we disagreed with the arguments themselves," he told Live Science.
Jay Olshansky, a biodemographer at the University of Illinois at Chicago who did not take part in either the previous work or the new studies, found the rebuttals "a bit amusing." He said the key problem with all of these arguments about maximum human life span is that, of the 108 billion or so humans ever born, "only a handful have ever lived to extreme old age beyond age 110, and it's only in recent times that the number of centenarians has risen."
"The rebuttals are mostly focused on slightly different ways of looking at the same limited data," Olshansky said. "Basically, if you tilt your head a little to the left or right and look at the same old age mortality or survival statistics for all humans, you might come to slightly different conclusions."
Future research should analyze the statistics of human aging as well as the human genome, which "will tell us whether people that have particularly long lives have a particular genetic makeup and whether this makeup changes with changes in the average life span," Hekimi said. "Carrying out such studies and finding out will take a while."
The five new studies are detailed online June 28 in the journal Nature.
Original article on Live Science.
