Research, published this week in Nature, argues that humans have already achieved their maximum possible lifespan. The investigators believe that the oldest people on record have hit the ceiling of longevity.
Alongside improvements in healthcare and diet, the human lifespan has steadily increased.
From 1900-2016, average life expectancy has gradually risen. Today, babies born in the United States can expect to live to 79. In 1900, it was just 47.
Since the 1970s, the age of the oldest people on earth has also risen. However, researchers from Albert Einstein College of Medicine, NY, believe that we have now touched the upper limits of maximum age.
Until now, scientists have considered that there is no particular reason why maximum lifespan should stop increasing. Studies in animals have shown that maximum lifespan is flexible and able to be altered by genetic and pharmacological interventions.
Also, a Swedish study found that maximum reported age at death has risen from 101 in the 1860s to 108 in the 1990s.
The plasticity of animal lifespans and humanity's ever-increasing average lifespan have lead biologists and demographers to believe that there is no ceiling on the maximum length of life.
Senior author of the current study - Prof. Jan Vijg, Ph.D., chair of genetics, the Lola and Saul Kramer Chair in Molecular Genetics, and professor of ophthalmology and visual sciences at Einstein - disagrees. He says: "Our data strongly suggest that it has already been attained and that this happened in the 1990s."
Delving into longevity
The Human Mortality Database collates information regarding mortality and population data from over 40 countries. Dr. Vijg and his colleagues analyzed this data and found that each birth year saw a larger fraction of people surviving beyond the age of 70.
This in itself points toward a steadily increasing average life expectancy. However, when the team investigated survival improvements for people aged 100 and above, since 1900, a different picture emerged.
When studying this older cohort, they saw that gains in survival peaked at around the age of 100 and then dropped rapidly - irrespective of the year they were born.
"This finding indicates diminishing gains in reducing late-life mortality and a possible limit to human lifespan."
Prof. Jan Vijg
To further understand this finding, the team looked at maximum reported age at death in the International Database on Longevity. Specifically, they looked at people who reached 110 or older anywhere between 1968-2006 in the four countries with the largest numbers of people reaching these ages: U.S., Japan, France, and the United Kingdom.
They found that the age at death for these supercentenarians increased swiftly from the 1970s to the 1990s. Then, in the mid-90s, they plateaued. French woman Jeanne Calment, who achieved the maximum documented lifespan of any person in history, died in 1997, aged 122.
A new maximum age
Despite Calment's extraordinary achievement, Prof. Vijg and his team put the average maximum human lifespan at 115. Calment was an outlier. And, they calculated the absolute maximum lifespan of a human to be 125 years.
Their findings mean that the probability of seeing someone live to 125 in any given year is 1 in 10,000.
"Further progress against infectious and chronic diseases may continue boosting average life expectancy, but not maximum lifespan.
While it's conceivable that therapeutic breakthroughs might extend human longevity beyond the limits we've calculated, such advances would need to overwhelm the many genetic variants that appear to collectively determine the human lifespan."
Prof. Jan Vijg
Perhaps, for some, this might be disappointing news, but Prof. Vijg sees it differently. He believes it may just prompt a shift in priorities: "Perhaps resources now being spent to increase lifespan should instead go to lengthening healthspan - the duration of old age spent in good health."