Radical extension of the human lifespan, science fiction or reality?
Humans have long been fascinated with maximizing lifespan, driven perhaps by a universal desire for more time. The 20th century witnessed a dramatic increase in average life expectancy at birth, thanks to improved sanitation, reduced infant mortality, decreased infectious diseases through antibiotics, and preventative treatment of cardiovascular diseases. However, the question remains: will this trajectory of rapid lifespan extension continue? A recent study examined mortality trends over the last three decades to determine if the projected average lifespan at birth is expected to keep increasing at rapid rates in the world's longest-lived countries.
Measuring Changes in Expected Lifespan at Birth
At the start of the 20th century, life expectancy at birth in the United States was about 47 years. By midcentury, it had risen to around 66 years for men and 71 years for women, eventually reaching approximately 78 years by the century's end. This 66% increase in life expectancy averages to about 0.33 years per year, the current standard for what is considered radical life extension (a yearly increase of 0.3 years, or 3 years per decade).
In the present study, investigators Olshansky and colleagues utilized annual age-specific and sex-specific death rates and period life expectancy at birth data from 1990 to 2019, sourced from the Human Mortality Database. They assessed whether the trend of radical life extension has continued over the past three decades in the eight countries with the longest-lived populations, including Hong Kong and the United States for comparison.
What the Study Found
The study revealed that the annual rise in life expectancy has largely slowed over the past thirty years. The defined 0.3-year annual or 3-year-per-decade improvement in life expectancy was only observed in South Korea from 2010 to 2019 and from 1990 to 2000 in Hong Kong. In most of the observed populations, the most recent decade (2010-2019) saw a decelerating annual rise in life expectancy at birth, dropping to below 0.2 years annually for eight of the ten populations. Additionally, most countries only increased survivorship to 100 years of age by 1-2% over the three-decade period, with slightly higher increases in Japan and Hong Kong, approximately 4% and 6%, respectively. However, none of these trends, even if they continued at the same rate, would lead to a 50% or greater survivorship to 100 by the next century.
The Challenge of Sustained Life Expectancy Increases
To continue increasing life expectancy, all-cause mortality (ACM) would need to be reduced at all ages by a greater percentage than was required thirty years ago. For example, in current-day Japanese men, a 9.5% reduction in ACM at all ages would be necessary to raise life expectancy from 82 to 83 years. For Japanese women, who already have a higher average lifespan, a one-year extension would require an astounding 20.3% reduction in ACM across all ages. These data suggest that as average life expectancy increases, each additional year of life requires increasingly significant reductions in mortality, making radical life extension more challenging in the longest-lived nations.
Interpreting the Data
Health improvements in the 20th century were largely due to better living conditions and the elimination or treatment of diseases, which occurred at different times across various nations. For instance, the radical rise in life expectancy in Hong Kong during the 1990s was attributed to economic prosperity and tobacco control, while Japan's later increase was linked to advancements in medical technology and the establishment of a national healthcare system in 1961.
These improvements were achieved by enhancing survivorship at all ages through disease reduction, not by altering aging-associated mortality. This distinction is crucial as humanity approaches the biological limits of aging. Similar to an oak tree, which can only grow so much before natural decline sets in despite protection from external threats, humans are likely approaching an upper limit to lifespan determined by the biology of aging itself.
The Future of Lifespan Extension
Olshansky et al.'s data indicate that while life expectancy has increased, maximum lifespan has stagnated, and lifespan variation has declined. This means that although people are living longer on average, the age at death is becoming more compressed into a narrower window, bringing humans closer to their biological limits without altering the fundamental processes of aging.
However, the study acknowledges that it cannot predict future advances in medicine or aging biology that might significantly impact lifespan. Potential breakthroughs in geroprotective drugs, genetic engineering, and human-machine interfacing could challenge the current understanding of aging and extend human lifespan beyond existing limits.
For example, geroprotective drugs like rapamycin have shown promise in increasing the lifespan of mice by 9-14% in the Interventions Testing Program (ITP). Genetic engineering has demonstrated significant lifespan increases in simple organisms like yeast and worms, hinting at possible future applications in humans. Moreover, advancements in technology, such as artificial brains and machine-brain interfaces, might redefine how we perceive and achieve lifespan extension.
The Bottom Line on Radical Lifespan Extension
While the study by Olshansky et al. suggests that radical lifespan extension through current methods is unlikely, it does not eliminate the possibility of future breakthroughs that could significantly alter this trajectory. Humans have a history of overcoming perceived limits, much like the development of flight or modern technology. Although there is no evidence to suggest humans can live to 150 years without transformative interventions, the potential for future advancements in aging biology and medicine remains open.
In the meantime, the best approach to reducing mortality risk and extending healthy lifespan involves maintaining a healthy lifestyle—regular exercise, a balanced diet, social engagement, and adequate sleep. These foundational practices offer the most reliable means of staying healthy and potentially extending lifespan within the current biological constraints.
Conclusion
The study by Olshansky and colleagues underscores the challenges in continuing the rapid increase in life expectancy seen in the 20th century. As we approach the biological limits of aging, each additional year of life requires more significant efforts to reduce mortality. While current trends suggest a slowing in life expectancy growth, the potential for future medical and technological breakthroughs offers hope for continued advancements in lifespan extension. Until then, embracing a healthy lifestyle remains the most effective strategy for enhancing longevity and quality of life.
Update from Peter Attia, on 2024-11-09Source