Arguing Against the Appearance of a Limit to Human Life Span in Historical Data June 30, 2017, 10:34

Life expectancy at birth is rising at about two years with every decade, while life expectancy at 60 is rising at about a year with every decade. The evidence in support of this trend is robust, thanks to the enormous demographic databases collected over the past few decades. Is this trend approaching any sort of limit to human life span, however? Can historical data even be used to answer that question? This is a much more challenging proposition, as the available data for the oldest humans, the population of supercentenarians older than 110, is sparse. Very, very few people survive to these ages, to the point at which statistical methods operating on this data become ever more dubious with each additional year of age.

Still, people crunch the numbers and try to extract meaning. You might recall that last year, Jan Vijg's group put forward their argument for the data to show there to be a limit to human life span over the years in which that data was collected. It was coupled to some unexpectedly pessimistic commentary on the future development of longevity science, given that Vijg has for some time been counted among those researchers openly in favor of extending healthy life spans by treating aging as a medical condition. The paper sparked some occasionally heated discussion. I don't think the researchers expressed their argument all that well in their publicity materials, and the popular science press then generated more than the usual degree of mess and confusion when they pitched in.

So to the casual observer, it was a little difficult to see whether Vijg and company were making the obvious point, which is that human life span is effectively limited by the present level of medical technology, or whether some more subtle argument was being made. I think it is hard to disagree with the statement that medical technology determines limits to human life span. Where we can debate, given the sparse nature of the evidence to hand, is whether or not there exists one or more mechanisms of aging that have not been impacted in any meaningful way by improvements in medical technology over the past century, and which, on their own, can produce a very high rate of mortality in late life. That circumstance would look a lot like a limit when examining the consequent demographic data.

One mechanism that springs to mind here is the accumulation of transthyretin amyloid, found in one small study to be the majority cause of death in supercentenarians, but which appears to have only a smaller impact on mortality in younger old age - it is implicated in something like 10% of heart failure cases, for example. Can we argue that advances in medicine and public health over the past century have had little to no impact on the accumulation of misfolded transthyretin deposits in tissues, and thus this mechanism acts as a limit on life span? Or do some of these improvements in fact produce an small, incidental reduction in amyloid burden in later life? I think that the evidence to support any of the possible positions on these questions is presently lacking.

Whatever the state of effective limits on life span today, however, the limits on life span tomorrow are determined by progress towards rejuvenation therapies. There are treatments under development that can clear transthyretin amyloid from tissues, for example. The same is true for many of the other forms of molecular damage and waste accumulation that cause aging. Thus any debate over what the present demographics do or do not show is more academic than it might otherwise be. The natural state of human aging, already largely paved over by medicine, will be buried completely, made irrelevant in the decades ahead by the advent of means to repair the damage, restore youthful function, and eventually to indefinitely postpone all of the symptoms of aging.

https://www.fightaging.org/archives/2017/06/arguing-against-the-appearance-of-a-limit-to-human-life-span-in-historical-data/