Association between intrinsic capacity and trajectories of physical function among older adults: findings from a 10-year longitudinal cohort study

Abstract

To identify trajectories of basic activities of daily living (BADL) and instrumental activities of daily living (IADL) and determine whether the baseline intrinsic capacity (IC) deficit score predicts 10-year functional decline in older adults. Data were from the Chinese Longitudinal Healthy Longevity Survey (2008–2018, N  = 2,045). A six-domain IC deficit score was constructed using the Integrated Care for Older People (ICOPE) framework. Group-based trajectory modeling, generalized linear models, and multilevel mixed-effects models (stratified by age) were used. Two BADL trajectories (high-stable 81.9%; high-declining 18.1%) and three IADL trajectories (mild, moderate, severe decline) were identified. A higher IC deficit score predicted declining BADL (odds ratio [OR] = 1.22, 95% confidence interval [CI]: 1.09–1.37), severe IADL decline (OR = 1.94, 95%CI: 1.66–2.27), and moderate IADL decline (OR = 1.37, 95%CI: 1.22–1.53). Each one-unit increase in the IC deficit score was associated with an additional annual BADL decline of 0.007 points (β = −0.007, 95% CI: −0.010 to −0.003, p = 0.001), equivalent to approximately 0.07 points over 10 years on the 0–6 scale. This effect was statistically significant but small in clinical magnitude and is better interpreted as a marker of preclinical functional change than as overt loss of independence. The IC × time association for IADL was not statistically significant in the primary complete-case analysis and was sensitive to missing-data assumptions. Annual IADL decline was greater for adults aged ≥80 vs. 60–79. A higher IC deficit score was associated with adverse physical-function trajectories and a small acceleration in BADL decline. Although the annual effect was unlikely to represent clinically perceptible loss of independence, it may indicate early functional vulnerability.