We are talking here of life expectancy at birth. And, it represents the average (or probably the median) number of years one can expect to live when born in a given year. This estimate is based on the current relevant mortality rate for each age-year.
We already have centenarians now. As a % of the population, the proportion of centenarians is likely to increase somewhat due to continuing progress in health care. However, health care improvement may be partly countered by deterioration in health trends (rising diabetes, obesity rate, and declining fitness levels).
To advance that in the near future we may reach a life expectancy of 100 is incredibly more challenging and unlikely than having a rising minority of the population reaching 100. Here is why... for each person who dies at a more regular age of 70, you need 3 who make it to 110. For each one who dies at birth, you need 10 who make it to 110.
How about 90? For each who dies at 70, you either need 2 who make it to a 100, or 1 who makes it to 110.
You can see how the average life expectancy arithmetic is very forbidding.
You can see my research on the subject at Slideshare.net and SlidesFinder.
The above is a 35 slides presentation that is very visual and reads quickly. Nevertheless, let me go over the main highlights.
I looked at the life expectancy of just a few countries with very long life expectancy plus China and the US.
Next, I looked at the UN forecasts of such life expectancy out to 2099. And, I found such forecasts incredibly optimistic.
As shown, all countries' respective life expectancy keeps on rising in a linear fashion by 1.1 year per decade. This seems highly unlikely. The longer the life expectancy, the harder any further increase becomes. The forecasts instead should probably be shaped as a logarithmic curve reflecting smaller improvements as life expectancy rises.
I did attempt to generate forecasts for a few countries (Japan and the US) using linear-log regressions to follow the above shape, but without much success. This was in part because the historical data from 1950 to 2020 is often pretty close to being linear ... just like the first half of the logarithmic curve above is also very close to being linear. Maybe if I had modeled Korea, I may have had more success using a linear-log model. But, there was no way I could have successfully used this model structure for all countries covered because the country-level historical data had often not yet entered its logarithmic faze (slower increase in life expectancy). The UN forecasts entailed that if the history was linear, the forecasts would be linear too ... a rather questionable assumption.
Also, as mentioned current deteriorations in health trends are not supportive of rising life expectancy... especially life expectancy keeping on rising forever in a linear fashion. I call this questionable forecasting method the danger of linear extrapolation.
As shown below, the rate of diabetes is rising worldwide.
Also, BMI is rising worldwide.
This deterioration in health trends represents material headwinds against life expectancy keeping on rising into the distant future.
The full presentation includes much more coverage on all the countries, more info on health trends; and it also looks at healthy life expectancy, a very interesting and maybe even more relevant subject than life expectancy. Who wants to live to a 100 if it entails 30 years of disability. Healthy life expectancy is what we really want. At a high level, healthy life expectancy is typically a decade shorter than life expectancy. For more detailed information go to the full presentations.
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