Dynamics of multimorbidity, health expectancy, and survival in middle aged and older individuals

Background: Life expectancy has increased, but such increase has disproportionally expanded the period of life with diseases. Whether expanding health expectancy (HE), defined as years of life free of chronic diseases, could also affect rate of multimorbidity accumulation is uncertain. Objective: to investigate the dynamic relationship between HE and rate of multimorbidity accumulation and their impact on survival. Methods: Four thousand two hundred seventy-four (3511 > 50 years) participants from the Health and Retirement Study (HRS), healthy at baseline and developing at least one disease overtime were included. Mean baseline age was 55.1 years and average follow-up was 9.4 years. Multimorbidity was operationalized as count of diagnosed diseases from a list of nine chronic conditions. HE was operationalized as years from birth until when the first disease was ascertained, and percentage of life in good health calculated as percentage of life lived free of chronic diseases. Mixed models investigated the association between HE and rate of multimorbidity accumulation, while survival analyses evaluated association with time to death. Results: HE were positively associated with multimorbidity rate (P < .001). Shorter HE and faster multimorbidity rate were independently associated with higher mortality (P < .001). Their interaction was negatively associated with mortality (P < .001). Results were confirmed restricting the analysis to individuals 51 or older and using HRS specific weights. Individuals with longer HE experienced a greater survival, almost regardless of multimorbidity rate, while a positive gradient was found in percentage of life in good health linked to multimorbidity rate. Conclusions: Expanding health expectancy is likely followed by compression of morbidity.