Today I'll point out an interesting paper on the demographics of aging, one that I hope indicates the spread of more nuanced and useful views into forecasts of the future of aging and longevity. While a good read, and helpful for our cause in that it will further spread the message that increases in healthy life span are both realistic and currently taking place, it is nonetheless still the case that this and all of the other long-term projections arising from the demographic community are essentially fantasies. They are simple extrapolations of trends in adult life expectancy established over the past few decades, and are thus based on a model of the future in which methods of rejuvenation are never invented and commercialized. In this future, progress in medicine consists only of incremental improvements to the present marginally effective therapies that attempt to patch over or compensate for the damage of aging. These treatments fail to repair or otherwise address that damage in any meaningful way, which is precisely why they produce only marginal outcomes at best.
This proposed continuation of the present gentle upward trend in life expectancy will not come to pass. The trend was established across decades in which no therapy attempted to address the cases of aging, the accumulation of molecular damage to cell and tissue structures that produces age-related disease and degeneration. Consider that for any failing machinery, it is very hard to keep it running when unable to fix the root cause of that failure. This is also the case for our biology: damage accrues, causing progressively greater system failures that we experience as age-related disease. Aging is no longer inevitable, however, as the first generation of rejuvenation therapies are even now nearing the clinic. To pick one example, selective destruction of senescent cells has been carried forward by venture funded companies these past couple of years, with human trials starting soon. Further, successful trials have been carried out in the past few years for clearance of forms of amyloid from old individuals, and again there is sizable backing for those lines of development.
Old age in the future of deliberate efforts to repair the damage that gives rise to aging will be profoundly different from old age in the past, in which medicine failed to address the causes of aging. There will be an abrupt upward discontinuity in the past trend of life expectancy, a sudden and considerably faster rate of increase in years of health and vigor. It is the difference between doing nothing for the causes of aging versus doing something to tackle those causes, and here and now is the dividing line between those two periods of development in medicine.
Traditional population projections categorize "old age" as a simple cutoff at age 65. But as life expectancies have increased, so too have the years that people remain healthy, active, and productive. In the last decade, researchers have published a large body of research showing that the very boundary of "old age" should shift with changes in life expectancy, and have introduced new measures of aging that are based on population characteristics, giving a more comprehensive view of population aging. The study combines these new measures with UN probabilistic population projections to produce a new set of age structure projections for four countries: China, Germany, Iran, and the USA.
One of the measures used in the paper looks at life expectancy as well as years lived to adjust the definition of old age. Probabilistic projections produce a range of thousands of potential scenarios, so that they can show a range of possibilities of aging outcomes. For China, Germany, and the USA, the study showed that population aging would peak and begin declining by 2040 in Germany and by 2070 in China, well before the end of the century. Iran, which had an extremely rapid fall in fertility rate in the last 20 years, has an unstable age distribution and the results for the country were highly uncertain. Population aging - when the median age rises in a country because of increasing life expectancy and lower fertility rates - is a concern for countries because of the perception that population aging leads to declining numbers of working age people and additional social burdens.
Probabilistic population forecasts were motivated by Keyfitz. Keyfitz wrote: "Demographers can no more be held responsible for the inaccuracy in forecasting population 20 years ahead than geologists, meteorologists, or economists when they fail to announce earthquakes, cold winters, or depressions 20 years ahead. What we can be held responsible for is warning one another and our public what the error of our estimates is likely to be."
There is now an extensive literature of probabilistic forecasting. All the probabilistic measures of aging produced by the United Nations assume that the threshold of old age is a fixed chronological age, regardless of time, place, education, or other characteristics of people. Researchers have questioned this assumption: "To the extent that our concern with age is what it signifies about the degree of deterioration and dependence, it would seem sensible to consider the measurement of age not in terms of years elapsed since birth but rather in terms of the number of years remaining until death." It is suggested the old age threshold be defined on the basis of some plausible remaining life expectancy rather than any specific chronological age. We call the ages, that are obtained when life expectancy is the characteristic that is held constant, prospective ages and measures that use them prospective measures of population aging.
New measures of population aging are useful because tomorrow's older people will not be like today's. They may well have longer life expectancies, better cognition, better education, and fewer severe disabilities. In most OECD countries, the labor force participation of people 65+ years old is increasing as are the ages at which people can receive a normal national pension. Since changes in the characteristics of people are ignored in the conventional measures of aging, they become more outdated with the passage of time. The use of prospective ages is one way to create measures of aging that are more in line with observable changes.
We chose a remaining life expectancy of 15 years. That was the life expectancy at age 65 in many low mortality countries around 1970. We show estimated and forecasted old age thresholds based on a remaining life expectancy of 15 years for China, Germany, Iran and the US for the years 2013 through 2098. In 2013, the old age threshold was 66 in China and 72 in Germany. By 2098, the old age threshold is forecasted to increase to 79 in Germany and 77 in China. Most of the population aging that we measure in China, Germany, and the US occurs between now and around 2040. The probabilistic forecasts show that it is highly likely that the prospective median age of the population of Germany and the US will be lower in 2098 than it is today. Even in China there is around a 50 percent chance that the prospective median age will be lower at the end of the century than it is today. It is possible that people's concern about the future is related to the number of additional years they expect to live. Lower prospective median ages in 2098 than now indicate that the people at the median age will have even more years of additional life ahead of them than people at the median age have currently, despite that median age being higher.