A limit to human lifespan?

Many demographers are fascinated by whether there is a limit to how long we can live.  The long-held record for lifespan is 122 years, and it doesn’t look as if that is going to be broken soon. The more pressing question is the pattern of life and death after age 95 or so.

Life expectancy is an indicator of the average lifespan of a population. We also know that, in nearly all countries, life expectancy has gradually increased over long time periods, and we are expected to keep living longer. Key questions in the study of ageing are to do with the relationship between the average and the maximum lifespan:

  1. will the average lifespan keep increasing to catch up with the maximum, so that everyone dies very close to the maximum, and
  2. will the maximum lifespan increase, and if so, to a limit or can it keep on going?

The longest known maximum lifespan in the world is over 122 years old.  Jeanne Calment lived in France from 1875 to 1997. The average lifespan for her cohort was 49 years. But the average is skewed by deaths at very young ages, and half of Mlle Calment’s cohort lived to age 59. However, only 1 per cent lived to age 96 and beyond. Living to age 122 was remarkable as even living into her 90s was very unlikely.

Compare to a cohort of today’s women. I’ll use data from England & Wales for convenience; the point is made even though we’ve switched countries. The cohort born in 2011 is the first in which half are expected to live to at least age 96. It has taken less than 140 years for the chances of reaching age 96 to increase from 1 per cent to 50 per cent. This shows the success of reducing deaths across a range of causes and at all ages from birth to old age.

The average lifespan expected for this cohort is 93 years – this is the cohort life expectancy indicator. The gap between average and median (the age to which half of the cohort can expect to live) is only 3 years, compared to 10 years for Mlle Calment’s cohort – the difference between age 59 and age 49. Then, many deaths occurred at young ages. Today, deaths are more likely to occur at old ages. This is the context for the first question above. In the jargon, mortality has been compressed towards the oldest ages – will it continue to compress still further?

The chances of living beyond age 96 have improved as well. So for our modern cohort, half are expected to live to age 96 and a third to age 100. But this does not necessarily point to the maximum human lifespan pushing out beyond Mlle Calment’s 122 years. After all, we have not yet seen anyone else living that long, even though each year more people live to age 100, which means the chances are increasing of more people aged 101, and more people aged 102 and so on.

The Office for National Statistics estimates there were fewer than 20 supercentenarians (people aged 110 and older) alive in the UK in 2014. There has been a discernible increase over the last few decades: see this chart. But these are still very small numbers on which to base a trend. On a global database of validated supercentenarians, there are said to be only 53 living. Only one of these is in the UK, which indicates the difficulty of reconciling actual numbers to population estimates.

We have little evidence to go on to help answer the second question. If there is a limit to human lifespan, we simply haven’t seen enough very old people to demonstrate it. In practical terms, it’s more important to understand the future prospects for compression of mortality at the very oldest ages – late 90s and into the 100s – so that we can understand healthcare needs and the likely limits of pension payouts.

 

This post was prompted by two interesting recent articles in The Gerontologist. One by Eileen Crimmins reviews evidence from the US to suggest that life- and health-spans there can continue to improve but that to increase the average beyond age 95 would require new medical technologies. Another by Hanayama and Sibuya estimates on the basis of mathematical modelling using Japanese data that the upper limit of human lifespan is 123 years.

 

Sources used in the above:

Calculations for Jeanne Calment’s cohort used data from the Human Mortality Database University of California, Berkeley (USA), and Max Planck Institute for Demographic Research (Germany). http://www.mortality.org. Data downloaded on 24 Jan 2016.

Calculations for the 2011 England & Wales cohort using data from E&W Life tables (1841-2064) based on actual and estimated historical mortality rates and projected mortality rates from the 2014-based principal population projections, ONS.
Data downloaded 25 Jan 2016.

Estimates of the population aged 90 and over in the UK, by sex, 1981 to 2014, published November 2015, ONS.
Data downloaded 25 Jan 2016.

 

 

3 thoughts on “A limit to human lifespan?

  1. Great article – longevity risk is definitely becoming a hot topic. The Society of Actuaries (USA) is actually dedicating a series of webcasts in 2016 to the topic, there should be some interesting findings coming out of those.

  2. Very interesting it seems that the age has definitely been extended I haves in nursing homes all my life and there has definitely been an increase in the years lived who knows where it ends

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