The path linking disease severity and cognitive function with quality of life in Parkinson’s disease: the mediating effect of activities of daily living and depression

BACKGROUND: Research on quality of life (QOL) with Parkinson’s disease (PD) has examined direct influencing factors, not mediators. The study aim was to explore whether PD severity and poor cognitive function may decrease physical and mental QOL by reducing activities of daily living (ADL) and increasing depression in sequence. METHODS: We conducted a cross-sectional questionnaire study of 150 PD hospital patients in China. PD severity, cognitive function, ADL, depression, and QOL were evaluated. We used structural equation modeling to analyze the mediating effects of ADL and depression on the association between PD severity/cognition and the physical health and mental health component summary scores measured by the SF36 quality of life instrument. RESULTS: There was a significant mediating effect of PD severity on physical health via ADL and depression (95% CI: − 0.669, − 0.026), and a significant direct effect (p < 0.001). The mediating effect of PD severity on mental health via ADL and depression was significant (95% CI: − 2.135, − 0.726), but there was no direct effect (p = 0.548). There was a significant mediating effect of cognitive function on physical health via ADL and depression (95% CI: 0.025, 0.219) and a significant direct effect (p < 0.001). The mediating effect of cognitive function on mental health via ADL and depression was significant (95% CI: 0.256, 0.645), but there was no direct effect (p = 0.313). The physical health models showed a partial mediation, and the mental health models showed a complete mediation, of ADL and depression. CONCLUSIONS: PD severity and cognitive function increase depression by reducing ADL, leading to lower QOL, and directly or indirectly affect physical health and mental health through different pathways.