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. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12877-020-01939-4.