Increases in life expectancy do not necessarily produce faster overall population aging, according to new open-access research published in the journal PLOS ONE.

This counterintuitive finding was the result of applying new measures of aging, developed at the International Institute for Applied Systems Analysis (IIASA) to future population projections for Europe up to the year 2050.

IIASA World Population Program Deputy Director Sergei Scherbov led the study in collaboration with IIASA and State University of New York, Stony Brook researcher Warren Sanderson.

“Age can be measured as the time already lived or it can be adjusted,” said Scherbov, “taking into account the time left to live.

If you don’t consider people old just because they reached age 65, but instead take into account how long they have left to live, then the faster the increase in life expectancy, the less aging is actually going on.”

Traditional measures of age simply categorize people as “old” at a specific age, often 65. But previous research by Scherbov, Sanderson, and colleagues has shown that the traditional definition puts many people in the category of “old” who have characteristics of much younger people.

“What we think of as old has changed over time, and it will need to continue changing in the future as people live longer, healthier lives,” says Scherbov.

“Someone who is 60 years old today, I would argue is middle aged. 200 years ago, a 60-year-old would be a very old person. The onset of old age is often used as an indicator of increased disability and dependence, and decreased labor force participation.

“Changing what we consider as the onset of old age is crucial to understanding population aging to create policies consistent with our current demographic.”

Three scenarios for future population aging

In the study, the researchers compared the proportion of the population considered “old” — using conventional measures labeling people “old” at age 65 — and the proportion based on a new measure of age that considers changes in life expectancy.

The study looked at three scenarios for future population aging in Europe, using three different rates of increase for life expectancy, from no increase to an increase of about 1.4 years per decade, the level projected by the Wittgenstein Center’s European Demographic Datasheet.

The results show that, as expected, faster increase in life expectancy leads to faster population aging when people are categorized as “old” at age 65 regardless of time or place, but, surprisingly, that they lead to slower population aging when the new measures of age are used.

 

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Abstract | Faster Increases in Human Life Expectancy Could Lead to Slower Population Aging

Counterintuitively, faster increases in human life expectancy could lead to slower population aging. The conventional view that faster increases in human life expectancy would lead to faster population aging is based on the assumption that people become old at a fixed chronological age.

A preferable alternative is to base measures of aging on people’s time left to death, because this is more closely related to the characteristics that are associated with old age. Using this alternative interpretation, we show that faster increases in life expectancy would lead to slower population aging. Among other things, this finding affects the assessment of the speed at which countries will age.