Social and biological pathways linking relationships with companion animals to human well-being.

Introduction: Companion animals are widely recognized for their potential to support human mental health and well-being. These benefits may arise through changes in social relationships and physiological processes. This study examined whether dog and cat ownership and attachment promote closer social relationships and higher well-being, the relative magnitude of direct and indirect effects of companion animals on well-being, and whether physiological factors, including cortisol concentration and gut microbiota composition, are involved in these processes. Methods: Two complementary studies were conducted. Study 1 used the Experience Sampling Method (ESM) to record daily social interactions over 2 weeks. Participants also completed questionnaires assessing pet ownership, attachment, social attitudes (including the Cultural Estrangement Inventory), self-esteem, general trust, and well-being. Structural equation modeling was used to examine direct and indirect pathways from human-animal relationships to well-being. Study 2 examined physiological correlates by analyzing urinary basal cortisol concentrations and gut microbiota composition. Results: In Study 1, dog ownership was associated with closer relationships with others. Family interaction was associated with well-being through two pathways: when confined to the household, it was associated with lower self-esteem and well-being, whereas when accompanied by interactions with the local community and friends, it was associated with higher self-esteem and well-being. These indirect effects were particularly pronounced among female participants, while no significant direct effects of companion animals on well-being were observed. In Study 2, lower cortisol concentrations were associated with greater daily conversation with close others, and gut microbiota profiles differed according to dog ownership and the frequency of family social contact. Discussion: These findings suggest that companion animals may contribute to human well-being through interconnected social and biological pathways. Dogs may promote well-being not simply by strengthening family relationships, but by facilitating broader social connections beyond the household. The findings also suggest that physiological processes, including cortisol regulation and gut microbiota composition, may be involved in the relationship between human-animal interactions and well-being.