Bidirectional Relationship Between Insomnia and Depressive Symptoms in Family Caregivers of People with Dementia: A Longitudinal Study.

Bidirectionality between insomnia and depression is well documented in general and clinical populations but remains under-researched in family caregivers of people with dementia. This study aimed to explore this relationship using a longitudinal design with 155 family caregivers assessed annually over three years. Data collected included sociodemographic information, health behaviors, medical data, caregiving stressors, and depressive and insomnia symptoms. Two linear mixed models were tested: Model 1 considered insomnia symptoms as the independent variable and depressive symptoms as the outcome; Model 2 considered depressive symptoms as the independent variable and insomnia symptoms as the outcome. The results showed that caregivers with more insomnia symptoms over time had significantly higher depressive symptoms, even after adjusting for covariates. Insomnia accounted for an additional 7.47% of the variance, with a total explained variance of 57.93%. Conversely, higher depressive symptoms over time were associated with increased insomnia. Depressive symptoms explained an additional 7.28% of the variance, with a total explained variance of 25.74%. These results were consistent with previous studies on non-caregiving populations, adding empirical evidence to the notion that both insomnia and depression may operate as a risk factor for the other disorder. Caregiver support interventions could improve their psychological well-being if they incorporate sleep-focused strategies.