Once you reach a very advanced age, you reach a sort of "aging plateau," according to some experts in aging. You get so old that your aging slows down. This idea is reasonably widely held, or at least taken seriously. But a new study suggests it could be result of a statistical error.
Here's how the theory of the aging plateau works: You continue to spend more years on Earth, but your body stops getting meaningfully older, or at least the rate at which it gets older slows down. Researchers call this effect "late-life mortality deceleration" or "LLMD."
Scientists began to wonder whether an aging plateau exists after studying the odds of dying during each specific year of life. When people reach the age of 90, it seems they're much more likely to die that year than they were at 75. But the odds of a person dying the year they turn 105, assuming they reach 105, aren't too much higher than they were when they turned 90. The very-very old and the very-very-very old are all more likely to die soon, but it's not clear whether the very-very-very old are much more at risk than the merely very-very old.
At least, that's what scientists thought. [8 Tips for Healthy Aging]
Now, a new paper published yesterday (Dec. 20) in the journal PLOS Biology suggests that this whole notion of an aging plateau is wrong — and instead, it's the result of a repeated statistical error. Researcher Saul Justin Newman found that a series of mistakes in the way aging data is collected and interpreted could explain most, if not all, of the evidence for an aging plateau in humans.
Newman told Live Science that most researchers who study aging accept the plateau as a given, even though there isn't a single agreed-upon biological explanation for why it might happen.
The problem, his paper argues, is that the evidence for the plateau is based on the assumption that ages are reported correctly to the databases researchers use. But some of those ages are probably entered incorrectly, Newman asserts. Seventy-five-year-olds could accidentally turn up in the database as 85-year-olds, and 98-year-olds could turn up as 84-year-olds.
But there are a lot more 75-year-olds who could get accidentally marked as older than there 98-year-olds who might get accidentally marked as younger. That means that the average senior has a better chance of being recorded as having died at an older age than they really were, rather than younger than they really were.
Newman found that just a handful of mis-recorded ages of death in a database could wildly skew the results, accounting for a large proportion of the error.
In a separate paper also published yesterday in the journal PLOS Biology, Newman challenged the findings of a specific paper published in June in the journal Science. That paper looked at a database of the lifespans of Italians and seemed to find evidence for a mortality plateau. Newman showed that an error rate of 1 in 500 seriously misreported ages could explain the results that study found.
Kenneth Wachter, a demographer at the University of California, Berkeley, and one of the authors of that paper, responded in a third paper, also published yesterday in the journal PLOS Biology.
"Newman offers a hypothetical scenario and shows that a certain stylized form of age misreporting can generate the appearance of a plateau," he wrote, pointing out that Newman didn't actually find any direct evidence for those errors in the data set.
For Newman's assumptions about reporting errors in that case to be correct, he pointed out, nearly every 110-year-old in the study would have to in fact be a 100-year-old with a misrecorded age. [Health Stats: The Best and Worst States]
"Such calculations tell us that [Newman's papers] imply wildly implausibly high rates of misreporting at extreme ages," he wrote.
There's just no evidence that this sort of error is actually present in the Italian data set, he added.
So what does this mean for the rest of us?
"This study [Newman's] reveals that human lifespan has upper limits," Newman said, adding, "Aging does not 'stop' in old age. Your biological machinery will get relentlessly worse from puberty until death."
The reality, according to Sara Hägg, an expert in molecular epidemiology focused on aging at the Karolinska Institutet in Sweden, is that aging is just not well-understood at a biological level. That makes claims of an ""aging plateau" difficult to account for, but also difficult to entirely dismiss, she said.
"When we look at trajectories using the epigenetic clock, which is a biological age measurement [based on chemical analysis] ... we actually see a deceleration effect in the oldest old," she told Live Science.
In other words, very old peoples' bodies exhibit some evidence of slower aging. But researchers don't attribute this to a plateau effect, she said, because it's possible that people who live to be that old are just slower agers.
"Today it is impossible to say what is the truth, although most data and results currently support technical artifacts [statistical issues] as explanations for the aging plateau, she said.
Originally published on Live Science.