Life expectancy has advanced in developed countries at unprecedented rates over the last 125 years: 32 years in the US, 34 in the UK, and approximately 35 (and perhaps more) in Japan for example. If life expectancy was to continue in a straight line, as it sometimes seems destined to do, our progeny could expect to live to close to 120, on average. It’s a pretty enticing future.
It's also likely a pretty fanciful future. A new forecasting study by researchers from the Max Planck Institute, the Institute for Demographic Studies in France, and the University of Wisconsin has found that the rate of longevity growth for current cohorts will likely decline by somewhere between 37% and 52% from previous generations. Using six forecasting methods, the researchers projected mortality for people born between 1939 and 2000. Every approach pointed to the same conclusion: the rapid improvements in life expectancy of the early 20th century will not continue forward at the same pace. To be clear, that doesn’t mean that life expectancy will decline in the future. Far from it. But the observed rate of increase over the last century (about half a year more, on average, for every birth cohort since 1900) will be smaller in the future.
In a way, it’s good news. Much of the decline in projected life expectancy comes from a diminished pace of mortality improvements at very young ages, with over half of the deceleration linked to trends of children under age 5. That sounds bad, but it really reflects the fact that we have made such large strides over the last century in reducing infant and childhood mortality, that future gains will necessarily be smaller in comparison.
Life expectancy has already hit stunningly high rates in some places: the median life expectancy for Japanese women is now almost exactly 90, and that will likely continue to grow into the future, but just not as fast as before.