The mediating role of pain-related disability in the relationship between biological rhythms and the severity of depressive symptoms in fibromyalgia

OBJECTIVE: To estimate the role of disability mainly in the link between chronobiological factors (sleep, light exposure, and rest/activity patterns) and depressive symptoms in people with fibromyalgia (FM). METHODS: A cross-sectional study was conducted on a cohort of 197 women, aged 18-65, diagnosed with FM. Depressive symptoms were measured using the Beck Depression Inventory-II (BDI), while FM-related disability was assessed through the Fibromyalgia Impact Questionnaire (FIQ). Actigraphy data (activity and light exposure) over 10 consecutive days and sleep-related behaviors were assessed. Mediation models were performed to investigate the direct and indirect (through FIQ) effects of chronobiological parameters on depressive symptoms. RESULTS: A negative Direct Effect (DE) was identified between BDI scores and light interdaily stability (DE = -4.89), as well as sleep duration on free days (DE = -0.81). There were also Indirect Effects (IE) through FIQ of both intradaily variability of activity rhythms (IE = 3.02) and sleep duration on workdays (IE = -0.47) on BDI scores. CONCLUSION: Our findings offer evidence that disability due to fibromyalgia symptoms mediates the relationship between rhythm fragmentation and severity of depressive symptoms, providing insights for improved care and therapeutic interventions in fibromyalgia.