Smaller, Older, Sicker: The SOS of Reduced Fertility and Increased Longevity
Editor’s note: This is the third article in the Public Health 101 blog series, which aims to keep users of Public Health 101 up to date on changes in public health and public health education. The series will be published throughout 2026 and 2027, leading up to publication of the 5th edition of Public Health 101 in spring 2028.
Each article highlights a change using a case study or key content that can be used in teaching. The series informs instructors on how the content relates to the 4th edition of Public Health 101 and to the upcoming 5th edition.
See the first article in the series here and the second article here.
Decreased fertility has become a defining demographic trend in the United States during the 21st century. Even more dramatic declines are occurring overseas, where similar patterns are occurring across Europe, Japan and increasingly, China.
Demographers estimate that an average of approximately 2.1 children per woman is required to maintain a stable population size. This is referred to as replacement fertility. In 2000, U.S. fertility rates were slightly above replacement, having declined from over 3.0 in the 1950s and 1960s. In the 2020s, fertility rates have fallen to approximately 1.6 and continue to decline. If sustained, this trend will eventually lead to a decline in the total U.S. population later in the century.
At the same time, increases in longevity — driven by advances in public health and healthcare — are reshaping the population. The result is a profound shift in age distribution, with the population aged 65 and older projected to more than double over the course of the century.
These challenges can be summarized as “smaller, older and sicker” (SOS), capturing the central demographic future facing public health.
The Impacts of Population Dynamics
Population projections show that while the number of people under age 18 and those aged 18 to 64 will remain relatively stable or decline modestly, the 65-and-older population will grow dramatically. This shift has several implications, and chief among them are:
- Increased prevalence of chronic diseases
- Greater demand for healthcare services
- Rising healthcare expenditures.
The Congressional Budget Office estimates that if current trends continue, healthcare spending could rise from approximately 20% to 40% of the U.S. gross domestic product by 2050. These levels are considered unsustainable.
Options for Addressing the SOS of Population Dynamics
Countries facing below-replacement fertility have implemented a range of strategies to increase birth rates. The most effective approaches, such as paid parental leave and subsidized childcare, have produced modest success but have not restored replacement fertility.
Other policy options include:
- Increasing immigration and facilitating workforce integration
- Extending retirement age to retain older workers
- Leveraging technology, including AI, to offset workforce shortages.
These strategies, even if politically acceptable, must be paired with efforts to address the health needs of an aging population. This must include chronic disease management, dementia care, and frailty prevention, plus research to identify more effective approaches. Such progress will require not only innovation in prevention and treatment, but also fundamental changes in how healthcare and public health systems are organized and delivered.
Implications for Public Health
Public health, by definition, focuses on populations. Thus, understanding population dynamics is essential to anticipating future public health challenges. The aging of the population is highly predictable: Those who turn 65 in 2050 are in their 40s today.
Responding to public health challenges stemming from population dynamics requires:
- Elevating prevention as the central strategy for improving health and controlling costs
- Expanding research investments to address chronic disease, aging and longevity
- Emphasizing cost-effectiveness in resource allocation decisions
- Redesigning systems to deliver high-quality care at lower cost
- Integrating population dynamics into public health education.
Incorporating the Healthy Aging Framework
Addressing the “older and sicker” components of the SOS dynamic requires a comprehensive approach to healthy aging. The Healthy Aging Framework developed by the Association of Schools and Programs of Public Health (ASPPH) provides a valuable structure for rethinking public health priorities in an aging society.
The framework emphasizes that healthy aging is not simply the absence of disease, but the maintenance of functional ability, independence, and quality of life. Its key principles, outlined below, are essential to addressing the challenges of an older, sicker population:
- Life course prevention: Health in older age is shaped by exposures and behaviors across the lifespan. Early and sustained prevention efforts are essential.
- Focus on health span: Extending years of independent, functional living is as important as increasing life expectancy.
- Social and environmental determinants: Age-friendly communities, social connection, housing, and transportation are critical to healthy aging.
- System integration: Coordinated efforts among public health, healthcare, and long-term care systems are needed to manage chronic conditions effectively.
- Workforce and caregiving capacity: Expanding and supporting the caregiver workforce is essential to meet growing demand.
This framework shifts the narrative from viewing aging populations as a burden to recognizing the opportunity to promote health, social participation, and well-being at older ages.
Implications for Public Health Education and Workforce Development
The SOS challenges and the ASPPH Healthy Aging Framework imply that the following concepts should be integrated into public health education and workforce preparation:
- Competency in population dynamics: understanding fertility, mortality and migration trends
- Prevention and health promotion skills across the life course
- Systems thinking and integration across healthcare and public health
- Policy analysis and economic evaluation, including cost effectiveness
- Interprofessional collaboration, especially in geriatrics and long-term care.
These content areas are consistent with expectations of the contemporary public health workforce and are reflected in the National Board of Public Health Examiners Certified in Public Health (CPH) exam.
Meeting the SOS Challenge
The convergence of decreased fertility and increased longevity will define the future of public health. The resulting SOS dynamic — smaller, older and sicker populations — presents both challenges and opportunities.
Addressing these realities will require:
- A renewed emphasis on prevention
- Integration of public health and healthcare systems
- Adoption of frameworks such as the ASPPH Healthy Aging Framework
- Transformation of public health education and workforce development.
The 4th edition of Public Health 101: Improving Community Health addresses many of these issues. The 5th edition (coming in 2028) will integrate population dynamics with the Healthy Aging Framework to provide a comprehensive, forward-looking core curriculum for undergraduate public health education in the 21st century.
About the Author: Richard Riegelman, MD, MPH, PhD, is the series editor for Jones and Bartlett Learning’s Essential Public Health Series and author of Public Health 101. Dr. Riegelman is Professor of Epidemiology, Medicine, and Health Policy, and Founding Dean of the George Washington University Milken Institute School of Public Health. He led the development of the Educated Citizen and Public Health initiative, which brought together arts and sciences and public health education associations to implement National Academy of Medicine’s vision for undergraduate public health education.
Dr. Riegelman earned an MD from the University of Wisconsin, and an MPH and PhD in Epidemiology from Johns Hopkins University. He practiced primary care internal medicine for more than 20 years. Dr. Riegelman has authored or edited more than 70 publications, including six books for students and practitioners of medicine and public health.