The mutual longitudinal mediating effects of psychological and physical disorders on cognitive impairment among older adults

Background
The potential mutual effect of physical and psychological disorders on cognitive function is critical for preventing cognitive impairment among older adults. We aimed to investigate the mediating role of physical and psychological disorders in their associations with cognitive function.

Methods
We conducted a prospective cohort study using the Health and Retirement Study, involving 5308 adults aged 60 years or older. Physical disorders included seven self-reported physician-diagnosed conditions. Psychological disorder and cognitive function were ascertained using the 8-item Centers for Epidemiologic Research Depression scale and the 27-point HRS cognitive scale, respectively. Multivariable linear regression models were used to assess the association of the baseline scores of physical and psychological disorders with subsequent cognitive scores. Second-order cross-lagged panel models (CLPM) were used to assess the longitudinal mediating roles, respectively.

Results
The higher psychological disorder scores (β = −0.15; P < 0.0001) and physical disorders scores (β = −0.18; P < 0.0001) were, the worse the cognitive function was. CLPM revealed a significant longitudinal mediating effect of baseline physical disorders through changes in psychological disorder from 2002 to 2010 on the cognitive scores changes from 2002 to 2010 (β = −0.02; P < 0.0001). Meanwhile, the longitudinal mediating effect of baseline psychological disorder scores through physical disorders changes from 2002 to 2010 on the cognitive scores changes from 2002 to 2010 was significant (β = −0.004; P = 0.005).

Conclusions
The mutual longitudinal mediating effects of psychological disorder and physical disorder indicate that among older adults, physical and psychological disorders accelerate cognitive impairment as a whole and mutually reinforcing process.