Bidirectional relationships between disability and cognitive decline: a 6-year longitudinal study

Disability and cognitive impairment are two significant age-related health issues in older adults. This study aims to simultaneously identify the bidirectional relationship between disability and cognitive impairment, and further pinpoint which one holds a more pivotal role in the relationship.

A total of 628 participants aged 66.0 (SD = 7.3) were retrieved from the 2000 and 2006 Social Environment and Biomarkers of Aging Study (SEBAS). Cognitive function was assessed using the modified Short Portable Mental Status Questionnaire (SPMSQ). Disability was measured as a count of activity of daily living, instrumental activity of daily living, and mobility scales. Structural equation models with cross-lagged analysis were used to examine the temporal relationship between cognitive impairment and disability over six years.

The cross-lagged model was well constructed (χ2 (9) = 34.5941, p < 0.0001, RMSEA = 0.0673, CFI = 0.99, SRMR = 0.03). Baseline disability significantly predicted future cognitive impairment (β=-0.25, p < 0.05), and baseline cognition significantly predicted future disability (β=-0.03, p < 0.05). Fisher's Z test indicated a stronger pathway from disability to future cognitive impairment compared to cognitive impairment to future disability (p < 0.001).

This longitudinal study suggested that disability and cognition change were bidirectional, with disability showing a stronger impact on future cognitive impairment. Further dynamic investigations and mechanisms between cognitive change and disability are warranted.