In 1997, at the age of 122, Zhanna Kalman died. She was the longest-living person in human history (at least among those whose deaths have been documented). But there will be others after it. According to new research published in Science, humans are nowhere near the maximum lifespan - if there is such a limit at all. By analyzing the mortality rate among 4,000 Italian centenarians aged 105 and above, scientists found that the risk of death - which increases over time throughout a person's life - suddenly decreases in the very old. If you live to 105, your chance of dying in that particular year is 50/50.
If this is proven among other populations, the leveling off of mortality - the “death plateau” -will have enormous consequences.
“If there is a plateau in mortality, there is no limit to human longevity,” says Dr. Jean-Marie Robin, a demographer at the French Institute for Health and Medical Research who was not involved in the study.
Battle for age
While scientists have long agreed that the risk of death increases steadily as a person ages until age 80, what happens next is the subject of a fierce debate between the two camps.
The first group believes that a person's life expectancy has a limitation. Back in 2016, Dr. Ian Vij of the Albert Einstein College of Medicine in New York City began a heated debate when his team discovered that human life was hitting a biological ceiling after about 115 years. In their study, the team consulted two international life expectancy databases to determine the likelihood that an older person could die in a particular year.
The results seemed clear: although the maximum human lifespan increased by about five years - to 115 between the 70s and 90s, the trend stopped in 1995. Despite medical innovations such as sanitation, antibiotics, vaccines, surgical techniques, people simply cannot die later. While long-living record holders such as Kalman certainly do occur, Vij's team concluded that a person's chance of living to 125 years of age is 1 in 10,000.
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The results make sense. All animals have a natural lifespan: dogs, for example, never live as long as humans, regardless of diet, exercise, or other wellness treatments. Biology also requires a hard limit. As we age, our DNA and proteins accumulate damage, transforming the body from a well-coordinated molecular mechanism into a heap of waste.
Even if age-related diseases did not kill you, at some point the body simply goes into failure. Superlong-livers, in particular, did not die of disease - Kalman, for example, died for an unknown reason - but still continue to die.
“Too many body functions fail,” Vij explained at the time. "The body can no longer live."
But it's too early to despair. Vij's research sparked a fierce debate among academics almost as soon as it hit the Internet. Some have argued that his statistical methods were flawed. Others said the findings were not based on sufficient data. Months after Vij's initial publication, five teams have spoken out with official criticism in a number of papers published in Nature.
“There is an alternative explanation,” says Dr. Maarten Peter Rosing of the Center for Healthy Aging at the University of Copenhagen, who co-authored one of the rebuttals at the time. "Maximum age just increases over time, and what we see as a decrease in life expectancy is actually a false conclusion based on visual research and statistics that cannot be considered that way."
Death plateau
New research bursts into this firestorm with a larger and better dataset.
Human demographers face two major challenges when studying life expectancy. First, not many people live to old age to collect enough statistics. Secondly, people tend to forget their age and self-reports can be ruined.
“At this age, it becomes difficult to prove that this age is real,” explains Dr. Elisabetta Barbie from the University of Rome.
To ensure the quality of their dataset, Barbie and her colleagues used a valuable resource: the records of every Italian aged 105 and older between 2009 and 2015. These individuals had birth and death certificates, which allowed scientists to confirm the exact age of each, avoiding the problem of "age exaggeration." For each of those who were alive at the time of the study, scientists issued a certificate of survival.
This dataset also allowed the team to track each individual over several years rather than grouping them by age intervals - a practice adopted in previous studies that use combined datasets. Tracking individual survival trajectories is an essential part of demography, especially in a relatively large sample of 4,000 people, about 450 of whom are men.
“I think this is the best data we could get,” says study author Kenneth Wachter.
The results showed that death rates skyrocket between the ages of 70 and 80 and that women live longer. But unlike previous datasets, these Italian super-centenarians have definitely shown that the risk of dying flattens to a plateau by age 105. The researchers also found that people born relatively late in the sample have lower mortality rates at age 105. Consequently, the plateau decreases over time.
“If the odds of survival are better at age 105, we're not hitting any hard limit,” says Wachter. Consequently, life expectancy increases.
"The results are very interesting and surprising," says Dr. Siegfried Hekimi, a biologist at McGill University in Montreal. Hekimi co-wrote a critical paper in 2017 in response to Vij's research. This study now provides the best evidence that mortality declines in extreme old age.
The new study has not been without critics. Dr. Brandon Milholland, who helped define the 115-year limit, says the new study was too limited and only observed a small fraction of the human population in one geographic area. It remains to be seen whether such results extend to the rest of humanity.
Why does death suddenly recede from the oldest?
The new study does not provide answers to this question, but the authors have several ideas. One of them is natural selection. Some people may have genes that make them more vulnerable to disease than others. Such people can die long before they reach the age of 105 and leave behind most of the elderly.
Another option - perhaps more interesting - is that at some point the body's repair mechanisms compensate for the damage. Super-livers can simply enjoy slower life at the molecular level: their cells don't divide as often and may have a lower metabolic rate, resulting in less damage.
We see this in cancer, explains study author James Vaupel. “Cancer is a fairly common cause of death in people in their 70s, 80s or 90s. But very few die of cancer over the age of 100.”
“The fact that there is such a plateau indicates that something is keeping the poor outcome in check at a large age,” says Wachter. We do not yet know what genetic effects are responsible for this inhibitory phenomenon, but they certainly appear at a young age - and finding them could be important for understanding aging and possible recovery.
The new study is unlikely to resolve the age dispute, but if the findings are proven through larger datasets, it will open up an incredible anti-aging opportunity. Many experts believe that very old people do not respond to medication. But if the likelihood of death does not increase with age at some point, then medication or calorie restriction interventions may help the oldest.
In other words, we can prevent death. Perhaps at any age.
Ilya Khel
