The Question of a Limit to Human Life Span

There has been much discussion in the aging research community these past few years on the topic of whether or not there is a limit to human life span, and how one might even go about defining such a thing. While life spans are in a slow upward trend due to general improvements in medical technology, can this trend continue without end, or will it run into a roadblock? In essence this is a debate over what can be extracted from poor data, and which data is in fact poor. Since there are few extremely old people, and since verifying age becomes ever harder the further back one has to go to search for records, the data for human mortality at advanced ages is very open to interpretation and reinterpretation, highly dependent on statistical methodologies used, and opinions on reliability of various sources of data.

In a more practical sense, this is all a storm in a teacup. Obviously there are mechanisms at work that ensure that even the statistical outliers don't make it much past 120. Autopsies carried out on supercentenarians revealed transthyretin amyloidosis, and consequent heart failure, as the dominant cause of death. It is reasonable to hypothesize that this form of age-related damage ensures the effective upper limit on human life span - in the sense that there is no hard limit, but if critical organ dysfunction ensures that mortality rates are 50% yearly or higher, then the odds catch up pretty quickly.

Equally obviously, all of this is absolutely dependent on the present state of medical technology. If transthyretin amyloid can be broken down, such as via the theraputic approach developed by Covalent Bioscience, then the result will be that everyone who periodically undergoes the treatment will live longer. The same goes for clearance of senescent cells, and all the rest of the SENS program of ways to repair the causes of aging. If medical technology addresses the damage of aging, then the length of life changes.

A related topic is the question of whether or not mortality rates stop increasing in very late life. Studies show that extremely old flies stop aging, in the sense that aging is defined as an increase in mortality rate per unit time. The flies have very high mortality rates, as is fitting for being in very poor shape, burdened by the damage of aging, but those very high rates appear to plateau. Over the past fifteen years, various analyses have suggested and then refuted that such a plateau exists in humans. Again we come back to the point that the data for very advanced ages isn't all that great, and so there tends to be a great deal of debate. At present, the balance of evidence and argument suggests that, for our species at least, mortality rates do keep increasing past the age of 110.

Are We Approaching a Biological Limit to Human Longevity?

Until recently human longevity records continued to grow in history, with no indication of approaching a hypothetical longevity limit. Also, earlier studies found that age-specific death rates cease to increase at advanced ages (mortality plateau) suggesting the absence of fixed limit to longevity too. In this study we re-examine both claims with more recent and reliable data on supercentenarians (persons aged 110 years and over).

We found that despite a dramatic historical increase in the number of supercentenarians, further growth of human longevity records in subsequent birth cohorts slowed down significantly and almost stopped for those born after 1879. We also found an exponential acceleration of age-specific death rates for persons older than 113 years in more recent data. Slowing down the historical progress in maximum reported age at death and accelerated growth of age-specific death rates after age 113 years in recent birth cohorts may indicate the need for more conservative estimates for future longevity records unless a scientific breakthrough in delaying aging would happen.

Many gerontologists are now more conservative regarding the future growth of longevity, citing results confirm that further growth of maximum lifespan for humans becomes an increasingly difficult task. Still there are reasons for cautious optimism here. Systematic analysis of human mortality throughout the 20th century revealed that, once a particular cause of death is accounted for, there is a proportional increase in both median age of death and maximum life span. So the authors of this study believe that application of aging-focused interventions could result in a continued increase not only in the median, but in maximal life span in humans as well.

Further research is needed to overcome obvious limitations of our study by addressing remaining concerns about data quality and representativeness, as well as increasing sample sizes. Still the data used in our study are the best available data so far, and their analysis suggests that there may be a provisional limit to human life in our current state of biomedical knowledge.