Researchers again estimated the maximum human lifespan at about 125 years, but a biologist who studies aging replied that this calculation applies only until we intervene in the aging process

Researchers again estimated the maximum human lifespan at about 125 years, but a biologist who studies aging replied that this calculation applies only until we intervene in the aging process

On July 7, Brandon Milholland, Xiao Dong, and Jan Vijg responded in Nature to criticism of their 2016 study. Saul Newman disputes the reliability of rare longevity records and accuses the authors of mathematical errors. They reply that he misrepresented both their conclusion and the mathematical basis of their work.

In the original study, the authors analyzed worldwide longevity records. Improvements in survival slowed sharply after age 100, while the age of the oldest person to die stopped increasing after the 1990s. The authors estimated a typical maximum of about 115 years. According to their calculation, the probability that at least one person would live beyond 125 in any given year was less than one in 10 000.

At the extreme end of the age distribution, a single incorrect record can shift the entire result. A woman who had already died was included in a validated database of supercentenarians: her son kept her body in a freezer and continued collecting her pension. In a separate demographic analysis, Newman compared US records with the introduction of complete birth registration. After states adopted complete registration, the recorded number of supercentenarians per capita fell by 69%. This figure is not the proportion of false records. The exact number of errors and cases of fraud remains unknown.

In a study of 3 836 Italians older than 105, the annual probability of death remained close to 47.5%. It was slightly lower in later birth cohorts. In this Italian sample, every year after age 105 was much like a coin toss.

As more people reach age 110, the chance of a new record increases even if the risk of death remains unchanged. A 2021 forecast estimated about an 89% probability that someone would reach age 126 by the end of the century, and about a 13% probability that someone would reach 130. The model assigns a nonzero probability to every subsequent age, but only about half of the preceding group remains alive after each year.

In their recent response in Nature, the authors rejected the claim that they had proposed an “absolute limit to survival,” but retained their estimate of a maximum near 125 years. João Pedro de Magalhães, a professor who studies the molecular mechanisms of aging, responded:

“This is true only until we intervene in the aging process. Humans cannot fly, but technology has allowed us to overcome natural limitations.”

In June, de Magalhães reviewed gene therapy for aging: modifying certain genes has already extended lifespan in mice, but researchers still cannot deliver such therapy safely to every tissue in the human body. Human studies have not yet shown a substantial reduction in mortality after age 110.

The 2016 calculation was based on annual worldwide longevity records, while the 2021 forecast used the number of people older than 110 and their risk of death. Both project current age-specific mortality into the future. If a therapy lowers the annual risk, more people will survive from each birthday to the next. A model based on earlier deaths would then cease to predict future longevity records.