Life Expectancy and Health Expectancy in the Twenty-first Century: The Unthinkable, the Inconceivable, and the Unknowable.

The last century witnessed an unprecedented rise in life expectancy; however, in recent decades the "unthinkable" has occurred-life expectancy stagnation, a dramatic drop in the U.S. international life expectancy ranking, rising midlife death rates, and widening socioeconomic and geographic disparities. The "inconceivable" has occurred with the high level of mortality from the COVID-19 pandemic in the United States, which further exacerbated racial, ethnic, and socioeconomic disparities and highlighted the vulnerabilities of long-term care systems and fragmented health policies. The "unknowable" future of mortality is explored through the lens of emerging work in geroscience based on an integration of biology with studies of aging populations, which offers some promise of potential interventions in the process of aging that underlies chronic disease resulting in mortality at older ages. However, transformative changes in social policy, health equity, behaviors, and legal rights are needed for the United States to improve its current situation. While the integration of biological understanding is likely to point to new avenues for improving population health and life expectancy, without immediate social changes, only a portion of the U.S. population is likely to be able to take advantage of these improvements, and the United States is likely to lag other countries in the level of life expectancy.