Scientists Rethink Maximum Life Expectancy After Study on World's Oldest People

As medical advances enable us to extend our lives, a question remains: how long can humans live? Thanks to scientists who have found the risk of dying plateaus at 105, we could be one step closer to an answer.

The ceiling for how long a human can live is a difficult area to study due to a lack of reliable data on the deaths of people who have reached an extreme age. Dying aged 122 in 1997, Frenchwoman Jeanne Calment so far holds the record for the longest confirmed human lifespan.

To further our understanding of aging, scientists wanted to investigate whether mortality rates continue to rise as we age, or eventually plateau until the chance of dying remains constant.

According to the authors of a study published in Science, humans have not yet reached their maximum life expectancy. And the probability of dying stops increasing at 105.

Scientists investigated thousands of elderly Italian people to gain a better understanding of life expectancy. Getty Images

The team arrived at this conclusion by estimating the mortality rates of 3,383 Italians who were aged 105 years or older between 2009 and the end of 2015.

Death rates, they argued, increase exponentially as we grow older. But when we reach 80 death rates decelerate, plateauing after 105. The mortality rate of those aged over 105 drops a little across groups born within the same year. The authors believe this suggests human lifespan will continue to increase over time.

Dr Jean-Marie Robine at the French National Institute of Health and Medical Research, who was not involved in the study, told Newsweek: "The results suggest this plateau but cannot confirm it because the sample size is too small."

"If it [the study's conclusion] is true, there is no biological limits to human longevity," he explained. The only limits would be the size of the world population, he argued.

There are a variety of reasons for the leveling out of mortality rates, he suggested. Firstly, because the frail die first. He also pointed to the theory that the risk of death increases with time because many hits are needed to kill off a young individual, whereas one hit is enough for the oldest. Therefore the risk of morality becomes constant. In addition, older people are generally removed from danger—for instance by living in a nursing home.

Dr. Jeroen Spijker of the Centre for Demographic Studies, who did not take part in the study, told Newsweek that while the study was sound, further data is needed to prove that there is in fact a mortality plateau beyond 105.

"The fact that these cohorts survived to age 105 makes them quite different to those who didn't. With this in mind, perhaps a leveling off in the death rates is just a logical consequence," he argued.

But this this does not automatically mean that there is no limit to a maximum life expectancy, he said. "While we can't look into the future, based on a simple indicator there appears to be more of an argument that mortality is only being compressed than a real mortality shift to extremely older ages: the change in female life expectancy at age 105 and the time trend in the age at death of supercentenarians." In the case of Italy, as well as other low mortality countries including Japan, he said this has not changed since the year 2000.

He added: "The studied cohort survived the Spanish flu and two world wars but was hardly exposed to smoking and diets high in saturated fat, animal proteins and calories. Younger generations reaching old age, on the other hand, are much more heterogeneous in terms of health behavior and have benefited much more from medical technology.

"Given the continued improvements in the latter, it will become 'easier' for younger cohorts to reach extreme ages, thus reducing the selection effect into old age."

He concluded: "The million-dollar question is therefore whether we will continue to see this leveling off in mortality at extremely high ages in the future."