Slowing Disease Accumulation but Persistent Complexity: Multimorbidity Dynamics from Age 70 to 100 in the Swedish Population

Karin Modig , Karolinska Institutet
Yuge Zhang, Karolinska Institutet
Katharina Schmidt-Mende, Karolinska Institutet
Sven Drefahl, Stockholm University
Marcus Ebeling, Max Planck Institute for Demographic Research

Background: At the individual level, diseases accumulate steadily with age. At the population level, however, selective survival may alter this trajectory, producing an apparent slowing of disease accumulation in advanced ages—analogous to the mortality plateau seen in demographic studies. Whether such dynamics extend to multimorbidity remains unclear. Methods: Using nationwide registers covering the entire Swedish population, we followed birth cohorts born in 1920–1922 from ages 70 to 100 to examine how morbidity and multimorbidity evolve over three decades of late life. We analyzed age-specific changes in disease accumulation and assessed the role of selective survival in shaping population-level patterns of disease prevalence and complexity. Results: Disease accumulation accelerated with age but decelerated beyond age 90, largely due to slower transitions from having few to multiple conditions. In contrast, individuals with five or more diseases showed relatively stable accumulation from ages 85 to 100. Cardiovascular diseases dominated the morbidity burden at all ages. Although overall accumulation slowed in the oldest-old, multimorbidity complexity persisted, with new disease combinations—especially among cardiovascular conditions—continuing to emerge. Conclusion: This population-based study reveals the natural course of multimorbidity in late life. While the rate of disease accumulation flattens after age 90, the complexity of disease combinations continues to increase. These findings challenge the notion that late-life populations become healthier through selective survival and highlight the need for health strategies that address not only disease counts but also the growing complexity of multimorbidity in aging societies.

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 Presented in Session 10. Non-Communicable Diseases and Cardio-Metabolic Health