Hair Cortisol Concentration among Siblings Caring for a Parent with Dementia: A Dyadic Approach to Sibling Relationship Quality and Perceived Caregiving Stress

Objective: Sibling relationship quality and perceived caregiving stress contribute to dementia caregivers’ well-being. However, few studies have examined the biopsychosocial mechanisms underlying sibling interdependence in the caregiving context, particularly using cortisol. The aim of this study was to examine the dyadic associations between sibling relationship quality (i.e., closeness, tension, ambivalence: simultaneous positive and negative feelings), perceived caregiving stress (i.e., emotional and physical stress experienced by caregivers) and hair cortisol concentration (HCC) among siblings caring for a parent with Alzheimer’s disease and related dementias (ADRD). Methods: Data came from 66 sibling dyads ( M age=56.5; 91% women) caring for a parent with ADRD. Participants reported their sibling relationship quality and perceived caregiving stress through a self-report survey. Cortisol was extracted from hair samples using optimized liquid chromatography-tandem mass spectrometry. Results: The actor-partner interdependence model revealed that individuals exhibited higher HCC when they felt emotionally closer to their sibling (i.e., actor effect), as well as when their sibling reported greater ambivalence toward them and more severe emotional caregiving stress (i.e., partner effects). Neither the actor nor partner effects of sibling tension or physical caregiving stress on HCC were significant. Conclusions: This study contributes to the understanding of the biopsychosocial processes shaping siblings’ experiences in parental dementia caregiving by highlighting the dyadic associations between sibling relationship quality, perceived caregiving stress, and HCC.