It’s considered an inescapable fact of life: the older you get, the more likely death becomes. But new research suggests that the chances of dying may level off – at least for those who make it to 105 years old.

The study found that death rates, which rise exponentially in adulthood, begin to decelerate after 80 years old and appear to eventually plateau, or even decline slightly, after the age of 105. By that point, the chances of passing away in a given year are approximately 50-50.

“It’s the equivalent of tossing a coin each year,” said Prof Jim Vaupel, a specialist in ageing at the Max Planck Institute for Demographic Research in Germany and one of the authors.

The findings add fuel to an unusually hostile debate between two camps of scientists, who are locked in an escalating dispute about whether humans are approaching their upper limit in terms of lifespan.

The latest paper, from Vaupel’s team who argue there is no evidence of a looming longevity limit, is based on data tracking the survival trajectories of almost 4,000 Italians older than 105 between 2009 and 2015. And they believe it bolsters their position.

“If [mortality] stays constant, as more and more people survive to very old ages, the record will be broken,” said Vaupel.

The latest study is not the first to tackle the question of what trajectory the human mortality curve takes for those who survive into extreme old age. However, previous efforts were hindered by small sample sizes and a failure to meticulously check birth records. “Age exaggeration is common among the oldest old”, according to the analysis in the journal Science.

Demographic data suggests that the chance of dying at 68 is around 2%, rising to 4% at 76 and 30% by 97. This doubling in the chance of death every eight years, known as the Gompertz law, implies an intrinsic ceiling to the human lifespan as the chance of death would hit 100% at around 111. But the data showed that instead of continuing to double, the risk of dying levelled off.

One explanation for the result is purely statistical: those who die in a certain age group in a given year tend to be the frailest. The following year, the survivors are one year older, but they are also relatively stronger and healthier. “Eventually the two factors, the ageing and the weeding out, counterbalance each other,” said Vaupel.

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Biological factors may also play a role. Cancer, for instance, becomes less common in the oldest people alive, which some have put down to a slow-down in cell division in this age range. “Cancer is quite a common cause of death for people in their 70s, 80s or 90s,” said Vaupel. “But very few people die from cancer over 100.”

Similar mortality plateaus are observed in a range of other species, including fruit flies and nematode worms, which the scientists said could hint at a common evolutionary explanation. Other animals, including certain fish and tree species, follow the reverse pattern, with the chances of death lessening for each year alive as they continue to grow in size.

The oldest human to have lived, according to official records, was Jeanne Calment, a French woman who died at the age of 122 years in 1997. Some claim the fact that this record has not been broken, despite an expanding pool of centenarians, is evidence that humans cannot live much beyond this age. And the latest findings appear to have escalated the ongoing debate.

“It seems rather far-fetched that after increasing exponentially, the chance of dying should suddenly stop in its tracks,” said Jan Vijg, a geneticist at Albert Einstein College of Medicine in New York. Vijg previously published a paper in Science’s competitor journal, Nature, suggesting that the human species has hit its maximum shelf-life that prompted five separate teams to submit critiques of the work. “I do not consider the evidence for a plateau presented in this paper to be especially strong,” Vijg added.