Preplanned Studies: A Multi-State Model Study of the Disability-Free Life Expectancy Among Older Adults with Chronic Multimorbidity Based on CHARLS — China, 2011–2020

The World Health Organization (WHO) defines multimorbidity as the coexistence of two or more chronic diseases in an individual (1). In China, the prevalence of multimorbidity among older adults is approximately 50%, with resulting disabilities and cognitive impairments posing a significant threat to their health (2). As the number of chronic diseases continues to increase, the patient’s physical function gradually declines, and the risk of activities of daily living (ADL) disability increases (3). While previous studies using traditional statistical methods have identified combinatorial patterns and influencing factors of multimorbidity, they often fail to explain the dynamic relationship between multimorbidity and disability during the aging process (4). This study addresses this gap by using data from the China Health and Retirement Longitudinal Study (CHARLS) to construct a multi-state Markov model (MSM). This model explores the risk ratio and transition probabilities between ADL independence, disability, and death in adults aged 60 years and older in China, estimating both life expectancy (LE) and disability-free life expectancy (DFLE) with and without multimorbidity. Our findings indicate that multimorbidity significantly increases the risk of disability and reduces both LE and DFLE in older adults. This study provides a comprehensive assessment of the dynamic impact of multimorbidity on the functional status and mortality risk of older Chinese adults, offering valuable insights to policymakers developing targeted health interventions.

Data were drawn from five waves of the CHARLS collected between 2011 and 2020. The study sample included adults aged 60 years and older at baseline with complete information on ADL, chronic conditions, and mortality during the follow-up. Sample size and composition for each wave are presented in Table 1. CHARLS ascertained chronic disease information through respondent self-report, including hypertension, dyslipidemia, diabetes, cancer, chronic lung disease, liver disease, heart disease, stroke, kidney disease, stomach or other digestive disease, emotional, nervous, or psychiatric problems, memory-related disease, arthritis or rheumatism, and asthma. Multimorbidity was defined as having at least two chronic diseases. The ADL scale used in CHARLS includes six indicators: eating, dressing, getting in and out of bed, bathing, using the toilet, and controlling urination and defecation. Disability was defined as limitations in two or more ADLs (5). Health state (ADL independence, disability, and death, Supplementary Figure S1) transition probabilities and risks were calculated using R (4.3.1, R Foundation for Statistical Computing, Vienna, Austria). An MSM was used, assuming that health state transitions depend only on the current state and can occur multiple times between observation periods. The maximum likelihood method was used to estimate parameters and obtain health state transition probabilities for different characteristic groups (6). Age- and sex-specific LE and DFLE by multimorbidity status were estimated using the micro-simulation method in SAS (version 9.4, SAS Institute Inc, Cary, USA). A cohort of 100,000 individuals aged 60 years and older was simulated, and survival time in different health states from age 60 to death was obtained by controlling the cohort’s health and survival trajectory.

Table 2 demonstrates that multimorbidity is a significant risk factor for transitioning from an independent state to disability [hazard ratio (HR) 1.49, 95% confidence interval (CI) 1.25, 1.77]. However, multimorbidity did not significantly affect transitions from independence to death, recovery from disability, or disability to death.

As shown in Supplementary Table S1, multimorbidity significantly affected LE, DFLE, and the percentage of DFLE in older adults, with variations observed across gender and age. Specifically, multimorbidity had a more pronounced adverse effect on the LE and DFLE of males younger than 75 years, while its impact was greater on females aged 75 years and older. The percentage of DFLE exhibited a consistent decline across genders before the age of 75, but a steeper decline was observed among males aged 75 years and older.

Figure 1 illustrates the influence of multimorbidity on LE, DFLE, and the proportion of disability life expectancy (DLE) to LE (DLE/LE) in older men and women. Multimorbidity significantly impacts DLE/LE, exhibiting age-related variations. Before age 75, men have a slightly lower proportion of DLE/LE than women. However, around age 75, the proportion for men surpasses that of women and increases at a significantly faster rate, creating a widening gap. Conversely, without multimorbidity, DLE/LE ratio remains comparable between sexes and is not significantly affected by age.

Figure 1. 

Expected remaining lifespan and disabled life expectancy for males and females aged 60–90 with and without multimorbidity. (A) Females with multimorbidity; (B) Males with multimorbidity; (C) Females without multimorbidity; (D) Males without multimorbidity.

Abbreviation: LE=life expectancy; DLE=disability life expectancy; DFLE=disability-free life expectancy.