According to a study led by researchers at UC Berkeley and the Sapienza University of Rome, once an individual lives to 105 years, their chances of living another year level off.

The study followed about 4,000 Italian residents who were 105 years or older between 2009 and 2015, tracing their death trajectories. Researchers found that individuals who were between 105 and 109 years old had the same life expectancy as individuals 110 years or older — in short, as people reach extreme longevity, their odds of living level out and plateau.

Kenneth Wachter, UC Berkeley professor emeritus of demography and statistics  and the lead author of the study, said the study provides new information on the connection between human death trajectories and evolution.

“Leveling out is important, as well as practical, because … it improves our understanding of aging, (and) it shows that human mortality rates are behaving the same ways as other organisms,” Wachter said. “This study shows the connection between humans and very different sorts of organisms, like Mediterranean fruit flies, (and) what we have in common — we’re all products of evolution.”

In addition, this research builds on “the evolutionary basis of aging,” and “is a clue to deep evolutionary processes in human mortality,” according to Wachter.

Wachter’s research began nearly ten years ago, when he and Italian researchers noticed that the data collected from people who were 110 years or older sparked controversy because the data was not clean, as the elderly tend to exaggerate their ages. Thus, he began working with people he had known for more than 25 years to “gather better data that would speak for itself.”

Wachter worked with four co-authors from Germany, Denmark and Italy, and collaborated with the Max Planck Institute for Demographic Research, then led by UC Berkeley chancellor’s professor of demography Joshua Goldstein, to gather data for this study.

Wachter emphasized that the findings were unusually clear, as the researchers gathered extraordinarily accurate data about the ages used in the study.

“Demographers who are criticizing the article are expressing skepticism about this data, but these data are exceptionally clean,” Wachter said. “We have 4,000 cases — that is a huge number of cases, and in a single country, these data are really top-notch … (and are) the best data we have on extreme longevity.”

Although he worked with researchers around the world, Wachter stressed that UC Berkeley has long been a leader in the subject of human demography.

As for the future impacts of his research, Wachter said that although there would not be any immediate payoff, in 10 to 15 years it could help establish the interaction of genomic data with healthy aging and informed medicine, and relate humans’ genetic processes to these applications.

“We also found that even at extreme ages, death rates were getting a little better,” Wachter said. “That’s very optimistic in terms of saying that we’ve not yet reached a limit of how long people can live.”