每日跟讀#592: How Long Can We Live?
Since 1900, average life expectancy around the globe has more than doubled, thanks to better public health, sanitation and food supplies. But new study of long-lived Italians indicates that we have yet to reach the upper bound of human longevity.
“If there’s a fixed biological limit, we are not close to it,” said Elisabetta Barbi, a demographer at the University of Rome. Barbi and her colleagues published their research Thursday in the journal Science.
The current record for the longest human life span was set 21 years ago, when Jeanne Calment, a Frenchwoman, died at the age of 122. No one has grown older since — as far as scientists know.
In 2016, a team of scientists at Albert Einstein College of Medicine in the Bronx made the bold claim that Calment was even more of an outlier than she seemed. They argued that humans have reached a fixed life span limit, which they estimated to be about 115 years.
A number of critics lambasted that research. “The data set was very poor, and the statistics were profoundly flawed,” said Siegfried Hekimi, a biologist at McGill University.
Anyone who studies the limits of longevity faces two major statistical challenges.
There aren’t very many people who live to advanced ages, and people that old often lose track of how long they’ve actually lived. “At these ages, the problem is to make sure the age is real,” Barbi said.
Barbi and her colleagues combed through Italy’s records to find every citizen who had reached the age of 105 between 2009 and 2015. To validate their ages, the researchers tracked down their birth certificates.
The team ended up with a database of 3,836 elderly Italians. The researchers tracked down death certificates for those who died in the study period and determined the rate at which various age groups were dying.
It’s long been known that the death rate starts out somewhat high in infancy and falls during the early years of life. It climbs again among people in their 30s, finally skyrocketing among those in their 70s and 80s.
If the death rate kept exponentially climbing in extreme old age, then human life span really would have the sort of limit proposed by the Einstein team in 2016.
But that’s not what Barbi and her colleagues found. Among extremely old Italians, they discovered, the death rate stops rising — the curve abruptly flattens into a plateau.
The researchers also found that people who were born in later years have a slightly lower mortality rate when they reach 105.
“The plateau is sinking over time,” said Kenneth W. Wachter, a demographer at the University of California, Berkeley, who co-authored the new study. “Improvements in mortality extend even to these extreme ages.”
“We’re not approaching any maximum life span for humans yet,” he added.