Human life expectancy has increased through two distinct process; firstly a reduction in child mortality, and second a reduction in the burden of damage accumulated over an adult life span. Control of infectious disease has played a large role in both components of gains in life expectancy. The trend has been slow. In recent decades, something like 0.2 years of life expectancy at birth and 0.1 years of remaining life expectancy at age 60 have been added with each passing calendar year.
Life expectancy is an artificial measure, of course: it is the length of life remaining, on average, assuming that nothing changes in the state of medical science and public health practices. But there are always improvements. At present, the medical research community is shifting from a paradigm in which the mechanisms that cause aging were ignored, to a paradigm in which the mechanisms that cause aging are deliberately targeted. Meaningful slowing and reversal of degenerative aging are now on the table as options for the years ahead. This will cause considerable, and welcome, disruption to the slow historical increase in life expectancy. The future is bright.
A recent study analysed data from the Human Mortality Database (HMD), specifically looking at the probability of death at a given age. For various countries, including the US, Sweden, and Japan, individuals over 50 years had their mortality postponed, on average, by a decade for every age group (50s, 60s, 70s, etc.) from 1967 to 2017. In the example of Sweden, mortality remained constant more or less over the 19th and 20th centuries, until 1950 where an international life expectancy revolution took place.
This could be due to the colossal medical advancements that took place: the discovery of the structure of DNA, novel vaccines, the first successful kidney transplant, a novel antibiotic tetracycline, the first oral contraceptive and the invention of the internal pacemaker. Since then, life expectancy increased almost linearly at a rate of 2.5 years per decade all over the world. This same trend is observed in the longevity leader - Japan. Undoubtedly, the improvements in mortality stem from postponing it and thus prolonging both lifespan and healthspan. People are living longer due to being healthier and thus aging diseases are pushed back, developing later in life.
There are three predominant views on which longevity researchers speculate about the future of life expectancy: 1) life expectancy will rise, but more slowly that in the past due to reaching the 'limit'; 2) the same 2.5 year per decade increase in life expectancy will continue as in the past; 3) life expectancy will rise at a much faster rate due to biomedical advances, as previously seen in the 1950s. The future for longevity will differ from the past, as various mortality improvements play their part. A more effective public health strategy, along with devising treatments to cure aging diseases, such as dementia and cancer, would push out the current limits of healthspan and lifespan. Furthermore, developments in precision medicine, nanotechnology, regenerating tissues, and research on the biology of aging may all lead to slowing rates of aging.