Is the Association Between Late Life Morbidity and Disability Attenuated Over Time? Exploring the Dynamic Equilibrium of Morbidity Hypothesis.

Objective: There is evidence suggesting that the prevalence of disability in late life has declined over time while the prevalence of chronic diseases has increased. The dynamic equilibrium of morbidity hypothesis suggests that these patterns are due to the attenuation of the morbidity-disability link over time. This study aimed to test this assumption empirically.

Methods: Data were drawn from three repeated cross-sections of SWEOLD, a nationally representative survey of the Swedish population aged 77 years and older. Poisson regression models were fitted to assess the trends in the prevalence of Activities of Daily Living (ADL) disability, Instrumental ADL (IADL) disability, and selected groups of chronic conditions. The changes in the associations between chronic conditions and disabilities were examined on both multiplicative and additive scales.

Results: Between 1992 and 2011, the prevalence of both ADL and IADL disabilities decreased whereas the prevalence of nearly all chronic morbidities increased. Significant attenuations of the morbidity-disability associations were found for cardiovascular diseases, metabolic disorders, poor lung function, and psychological distress.

Discussion: In agreement with the dynamic equilibrium of morbidity hypothesis, this study concludes that the morbidity-disability associations among the Swedish older adults largely waned between 1992 and 2011.