Back to Arguing for a Mortality Rate Plateau in Extremely Old Humans

I'm of the opinion that there simply isn't enough data on extremely old humans to do more than roll the dice on the outcome produced by any one statistical analysis, though the results noted here are based on a large enough study population to perhaps demand more attention than past efforts. The researchers have avoided the very sparse data for supercentenarians (110 and older) by focusing on people aged 105 to 110. They conclude that mortality rates stay much the same across that span, at more or less a 50% yearly attrition. This disagrees with one of the more recent attempts to run the numbers for supercentenarian mortality rates.

Aging is defined as the increase of intrinsic mortality rate over time, and a lack of increase is therefore classed as functional immortality by some researchers. Not the useful, desirable sort of immortality, of course. This phenomenon has good supporting data in flies, a species that readily exhibits a late life mortality rate plateau. Whether this happens in mammals, and particularly in humans, is much debated. There are arguments on both sides. It is interesting to ponder whether this functional immortality represents only a temporary buffer in the state of a few critical systems, or would instead continue for much longer, were there enough data to follow mortality that far into physiological loss of function.

The answers may never be known. It is unlikely that many times more physiologically extremely old people than exist today will ever exist. Rejuvenation therapies will emerge over the decades ahead as a counterpoint to demographic aging. The natural state of aged humanity, the fate of everyone absent the ability to repair the root causes of aging, will come to an end. Whether the few survivors at the end of a natural lifetime are strangely immortal will be a question for future computational scientists and their advanced models, not future demographers. Given the lack of interest in modeling exact outcomes of extinct disease states today, I'm not convinced that future scientific and funding communities will care enough to investigate.

Researchers tracked the death trajectories of nearly 4,000 residents of Italy who were aged 105 and older between 2009 and 2015. They found that the chances of survival for these longevity warriors plateaued once they made it past 105. The findings challenge previous research that claims the human lifespan has a final cut-off point. To date, the oldest human on record, Jeanne Calment, died in 1997 at age 122. "Our data tell us that there is no fixed limit to the human lifespan yet in sight. Not only do we see mortality rates that stop getting worse with age, we see them getting slightly better over time."

Specifically, the results show that people between the ages of 105 and 109, known as semi-supercentenarians, had a 50/50 chance of dying within the year and an expected further life span of 1.5 years. That life expectancy rate was projected to be the same for 110-year-olds, or supercentenarians, hence the plateau. The trajectory for nonagenarians is less forgiving. For example, the study found that Italian women born in 1904 who reached age 90 had a 15 percent chance of dying within the next year, and six years, on average, to live. If they made it to 95, their odds of dying within a year increased to 24 percent and their life expectancy from that point on dropped to 3.7 years.

The researchers used data from the Italian National Institute of Statistics. They credit the institute for reliably tracking extreme ages due to a national validation system that measures age at time of death to the nearest day: "These are the best data for extreme-age longevity yet assembled." As humans live into their 80s and 90s, mortality rates surge due to frailty and a higher risk of such ailments as heart disease, dementia, stroke, cancer, and pneumonia. Evolutionary demographers theorize that those who survive do so because of demographic selection and/or natural selection. Frail people tend to die earlier while robust people, or those who are genetically blessed, can live to extreme ages.