A Discussion of Natural Limits on Lifespan, for Some Definition of Natural

A recently published analysis of the nature of limits to human life span under our present rapidly changing circumstances is receiving a lot of press attention today. The press being the press, you might skip the popular science articles in favor of the paper. Since it is not open access, you'll have to obtain it from the usual unofficial sources. It is an interesting read, and serves as a reminder that the research community actually knows very little about the demographics of aging at very advanced age. The data is so sparse past age 110 that the statistics of mortality, very reliable in earlier old age, rapidly turn into a sludge of uncertainty. It is possible at this point in time to argue either side of the position that there is or is not a limit to longevity under present circumstances, though most of us probably think that one or the other side is weak. On the one hand we can theorize that maximum human life span is increasing, in a way analogous to the fact that life expectancy at 60 is inching upward at a year every decade, but more slowly, and we might suggest the data for extreme old age is so bad that the ongoing change can't be identified. On the other hand we can instead theorize that there is some limiting process that hasn't changed at all over the course of recent human history, is not impacted meaningfully by modern medicine, plays a very large role in supercentenarians in comparison to younger old people, and renders mortality rates so very high at the extremes of human life spans as to form a limit.

This is actually a point worth making twice: when limits to lifespan are discussed, we're not talking about actual limits per se, but effective limits. A very large mortality rate, possibly coupled with rapid growth in mortality rate over time, looks a lot like a hard barrier to further progress in practice, but there is still the chance that someone could beat the odds. Where the data for supercentenarians is good enough to fill in tentative mortality rates with large error bars, up to age 115, that rate is around 50% annually. The mortality rate may increase greatly after that point, and that would be entirely expected given the absence of more than the one certified example making it past 120, but it is very unclear from the limited data. Mortality rates reflect actual physical processes, the accumulation of forms of cell and tissue damage that cause the suffering, death, and disease of old age. The damage is the same, but the proximate causes of death for supercentenarians are quite differently distributed from those of younger old people, prior to a century of age. The majority appear to be killed by transthyretin amyloidosis that clogs up the cardiovascular system, and that is becoming known to play a much lesser - but still significant role - in heart disease in earlier old age. Could this form of amyloidosis be the candidate for a process that is not all that affected by the past century of changes in medicine and lifestyle, and that becomes much more important in extreme old age than early old age? Possibly. The only way to know for sure is to build ways to clear this form of amyloid and see what happens.

The natural state of aging is a function of damage and how medicine addresses that damage - which is poorly and next to not at all at the present time. Almost all medicine for age-related conditions fails to address their root causes, the cell and tissue damage of aging, and takes the form of patching over that damage in some way or coaxing biological machinery to cope slightly better with running in a damaged environment. Predictably it is expensive and only marginally effective in comparison to true repair. As above in the comments on amyloidosis, find a way to repair that problem and life span will increase, as the machinery of biology will be less damaged and less worn down into high rates of failure. That is the point to take away from this discussion. It has to be said that the lead of the study, Jan Vijg, comes across as very pessimistic on aging in his comments here when considered in comparison to past remarks and collaborations with SENS folk that I've seen from him. That is the case even granting that he is in the camp of researchers who believe there is no alternative to a very slow and expensive reengineering of human metabolism in order make incremental gains in life span and slowing of the aging process.

What's the Longest Humans Can Live? 115 Years, New Study Says

On Aug. 4, 1997, Jeanne Calment passed away in a nursing home in France. The Reaper comes for us all, of course, but he was in no hurry for Mrs. Calment. She died at age 122, setting a record for human longevity. Jan Vijg doubts we will see the likes of her again. True, people have been living to greater ages over the past few decades. But now, he says, we have reached the upper limit of human longevity. "It seems highly likely we have reached our ceiling. From now on, this is it. Humans will never get older than 115." his is the latest volley in a long-running debate among scientists about whether there's a natural barrier to the human life span. "It all tells a very compelling story that there's some sort of limit," said S. Jay Olshansky, who has made a similar argument for over 25 years. James W. Vaupel has long rejected the suggestion that humans are approaching a life span limit. He called the new study a travesty. "It is disheartening how many times the same mistake can be made in science and published in respectable journals," he said. Dr. Vaupel bases his optimism on the trends in survival since 1900.

But when Dr. Vijg and his students looked closely at the data on survival and mortality,they saw something different. The scientists charted how many people of varying ages were alive in a given year. Then they compared the figures from year to year, in order to calculate how fast the population grew at each age. The fastest-growing portion of society has been old people, Dr. Vijg found. In France in the 1920s, for example, the fast-growing group of women was the 85-year-olds. As average life expectancy lengthened, this peak shifted as well. By the 1990s, the fast-growing group of Frenchwomen was the 102-year-olds. If that trend had continued, the fastest-growing group today might well be the 110-year-olds. Instead, the increases slowed down and appear to have stopped. When Dr. Vijg and his students looked at data from 40 countries, they found the same overall trend. The shift toward growth in ever-older populations started slowing in the 1980s; about a decade ago, it stalled. This might have occurred, Dr. Vijg and his colleagues said, because humans finally have hit an upper limit to their longevity.

Human lifespan may have maxed out

RG: Could you explain the research you did and the method you used in your analysis?

Vijg: We tested if human maximum life span is fixed or fluid and we found it to be fixed at around 115 years. We did this by looking at the maximum reported age at death in France, Japan, the United Kingdom and the United States. Firstly, we tested if improvement in survival also shifts to older age groups over time. We showed that improvement in survival in the oldest age group peaked in about 1980. This suggests - but does not prove - that we are reaching a maximum lifespan. Then we tested the maximum reported age at death since the 1960s. At first, this increased, but only up until the early 1990s. It then seemed to settle on a plateau, or even decline slowly, which is why we believe there is strong evidence that we have reached our ceiling.

RG: Why do you believe that humans have a natural age limit that is unlikely to be exceeded?

Vijg: Probably because the multiple longevity assurance systems humans have to prevent or fix damage and respond to stress are limited. This is also likely to be true for all animal species. A mouse lives much shorter than a human, possibly because it possesses inferior longevity assurance systems and can only get rid of damage and stress up until about three years.

Evidence for a limit to human lifespan

Driven by technological progress, human life expectancy has increased greatly since the nineteenth century. Demographic evidence has revealed an ongoing reduction in old-age mortality and a rise of the maximum age at death, which may gradually extend human longevity. Together with observations that lifespan in various animal species is flexible and can be increased by genetic or pharmaceutical intervention, these results have led to suggestions that longevity may not be subject to strict, species-specific genetic constraints. Here, by analysing global demographic data, we show that improvements in survival with age tend to decline after age 100, and that the age at death of the world's oldest person has not increased since the 1990s. Our results strongly suggest that the maximum lifespan of humans is fixed and subject to natural constraints.