Age trajectories of disability in instrumental activities of daily living and disability-free life expectancy among middle-aged and older adults in Taiwan: an 11-year longitudinal study

Background This study aims to identify the age trajectories of disability in instrumental activities of daily life (IADLs) over 11 years and their correlates, and to estimate disability-free life expectancy for identified trajectory groups in middle-aged and older adults. Methods We included 3118 participants aged 50 and over without IADL limitations at baseline from the Taiwan Longitudinal Study in Aging, followed across 1996-2007. We used group-based trajectory models to identify age trajectories of IADL disability, and multiple logistic regressions to examine their correlates. Sullivan method was used to compute IADL disability-free life expectancy for trajectory groups at different ages. Results We identified two trajectories groups: 67.7% of participants classified as the late-onset group and 32.3% as the early-onset group. Female (adjusted odds ratio [aOR]: 1.93, 95% confidence interval [95% CI]: 1.54, 2.41), not being employed (aOR: 1.30, 95% CI: 1,08, 1,56), poor/fair self-rated health (aOR: 1.31, 95% CI:1.09, 1.58), hypertension (aOR: 1.32, 95% CI: 1.07, 1.63), diabetes mellitus (aOR: 2.29, 95% CI: 1.72, 3.07), arthritis (aOR: 1.42, 95% CI: 1.11, 1.81), stroke (aOR: 2.21, 95% CI: 1.04, 4.70), and one-point increase in a 10-item depression scale (aOR: 1.04, 95% CI: 1.02, 1.06) were associated with early-onset of disability, whereas higher education (aOR: 0.59, 95% CI: 0.42, 0.81), regular exercise (aOR: 0.76, 95% CI: 0.62, 0.93), and participating voluntary or club activities (aOR: 0.78, 95% CI: 0.65, 0.93) related to the late-onset. IADL disability-free life expectancies at 65 years old in the late-onset group were 15.6 years for women and 14.4 for men, respectively, comprising 56.6 and 64.2% of their remaining life, whereas those of the early-onset group were 4.8 and 4.6 years for women and men respectively, comprising 22.5 and 27.2% of remaining life. Conclusions Early-onset of IADLs disability may correlate to chronic conditions, and engagement in employment, exercise, and social participation were associated with a reduced risk of early disability in IADLs.