For over a hundred years, human life expectancy in the most developed countries has increased steadily by three years per decade. But how long can that increase continue? This issue is the subject of lively discussions among researchers in the field.
The first time Chalmers researchers Holger Rootzén and Dmitrii Zholud published their theory that there is no upper limit to the human lifespan was in 2017. Since then, larger amounts of data have become available, and now a new study has reached the same conclusion: there is no statistical evidence for a human maximum age.
”With access to considerably larger amounts of data, we have been able to verify our previous results” says Holger Rootzén.
The result once again contradicts an earlier publication in the scientific journal Nature, in which it was concluded that the natural limit for human lifespan is 115 years.
”If there had been a limit below 130 years, it should have been discovered in the study, and that would have been an indication that the increase in life expectancy cannot continue indefinitely. But that is not the case” says Holger Rootzén.
Like tossing a coin
Knowledge about possible upper limits to the human life span is important for society, and can be a factor in, for example, the planning of pension systems. However, in the study no signs were found which suggest that human life expectancy cannot continue to increase. In fact, it seems that the chances of surviving another year increases rather than decreases at extreme old age. After the age of 108, the chances of living another year are like a tossing a coin, the researchers conclude. If it's heads, you'll live to the next birthday.
”If we had met Jean Calment, the world’s longest living person, who lived 122 years, when she had her 108 year birthday, we could have told her that she had to get heads 14 times in a row to reach 122. The chance is about 1 in 16,000” says Holger Rootzén.
As the number of individuals living for a very long time increases, so does the possibility that someone will reach, for example, 130 years. But if there are no medical revolutions, according to Holger Rootzén, it is unlikely that anyone in the next 25 years will live longer than 128 years.
No difference between men and women
Another interesting result in the study is that the differences in survival, between women and men, and between different lifestyles, that exist at younger ages vanish after 108 years of age.
”There seems to be no difference in mortality at old age between different countries or between women and men. We suspect that the plateau with a 50 percent risk of dying per year is a biological property that is common to all humans” says Holger Rootzén.
About the study
Data was collected partly through the International Database on Longevity, which contains over 1,100 so-called supercentenarians (persons over 110 years) from 13 countries* and also semi-supercentenarians (persons over 105 years) from some of the countries, and partly through data from Italy on all persons who were at least 105 years old between January 2009 and December 2015.
The researchers used a combination of extreme value statistics, survival analysis and computer-intensive methods to analyze the mortality of Italian and French semi-supercentenarians. The findings are consistent with previous analysis of the international database on life expectancy and suggest that any biological upper limit on human life expectancy is so high that it is unlikely that anyone will reach it.
*Austria, Belgium, Canada, Denmark, England, Wales, Finland, Germany, Norway, Spain, Sweden, USA.
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Links to media reports about the study
Photo: featured image Danie Franco on Unsplash. Portrait of Holger Rootzén: Helle Rootzén