Another study came out this week that suggested a future of human longevity unlike anything most of us have really considered. (In fact most of us don’t think all that often about the fact that the average human lifespan worldwide has doubled in the last century.)
Could that happen again – so that kids being born in a hundred years will expect to live to around 150?
A new study suggests it might at least be possible.
The bottom line from the study, published this week in the Journal Science: “human death rates increase exponentially up to about age 80, then decelerate, and plateau after age 105.”
In other words, if you can make it to 105, you’re statistically just as likely to live another year as not, at least for a few more years. So, if you’re 105, the odds you’ll make it to 106 are about 50-50. (Sorry to be the bearer of bad news – those aren’t really all that great odds). If you’re 106, your odds of getting to 107 are about the same – about 1 in 2. Same if you’re 109 – it seems about half the people who make it to 109, make it to 110. We don’t know if this continues indefinitely, because, at some point, with half of the people over 100 dying each year, you run out of people to study.
But, “our data tell us that there is no fixed limit to the human lifespan yet in sight,” study senior author Kenneth Wachter, a UC Berkeley professor emeritus of demography and statistics, said in a statement this week. “Not only do we see mortality rates that stop getting worse with age, we see them getting slightly better over time.”
It’s similar to the findings from a study last year published in the journal Extremes.
“We find that in western countries and Japan and after age 110 the risk of dying is constant and is about 47% per year,” the authors of that paper found.
The idea that your likelihood of death doesn’t skyrocket once you hit a very old age means there’s hope that medical technology could continue to prolong life. Or, as the authors of the article in Extreme wrote, “Data does not support that there is a finite upper limit to the human lifespan. Still, given the present stage of biotechnology, it is unlikely that during the next 25 years anyone will live longer than 128 years in these countries.”
Or, as the lead demographer on the study published Thursday in Science, Elisabetta Barbi, at the University of Rome told the New York Times, “If there’s a fixed biological limit, we are not close to it.”
While the data may not support the idea of eventually hitting some finite limit, there’s broad lack of agreement on the whole question, for the obvious reason that as long as there’s no record of anyone living past the current record of 122, we don’t really know if it’s possible. In other words, before the invention of the airplane, it was possible to fly in an airplane – if one had existed. But since nobody had made an airplane and done it, nobody knew for sure whether it was possible.
The Washington Post noted this week that a couple of things are increasing our lifespans – one is actually more of a statistical “trick.” That’s the reduction in infant mortality, which simply raises the average age at death by removing many of the very low numbers from the data set. That has improved remarkably in many parts of the world over the last century. But medical care of the elderly is also improving, actually increasing the number of people who are actually very “old.”
It’s worth noting that there are some aging experts who are skeptical that the plateau continues. The New York Times story cited researchers who posited a couple years ago that the upper limit was likely to exist, and that it was around 115. One of them was quoted by the Times this week, questioning the new study and standing by the older one. Currently, however, the oldest living person in the world is Chiyo Miyako of Japan, who is 116.
It’s also worth noting that there may be an interesting selection effect going on – people who live past 100 may be the strongest (genetically or otherwise) among us. That’s because the chances of continuing to live aren’t quite as good as you age when you’re under 100.
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.
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