Mapping the integration of adult friends into the study of close relationships and health

Close relationships are associated with many positive outcomes throughout life, including improved physical health and well-being. Traditionally, theory and research on the health benefits of close relationships have focused on either the total amount of support perceived available within a person's entire social network or the support provided by romantic partners (Shankar et al. in Psychology and Health, 30(6), 686–698; 2015). Limited work has examined the impact of distinct relationship types, particularly friends. In this article, we address this critical gap in our current knowledge. First, we identify the features of friends and friendship networks that distinguish them from other types of adult relationships, especially romantic relationships. Second, we use the strength and strain model (Slatcher & Selcuk in Current Directions in Psychological Science, 26(1), 16–21; 2017) as a framework to consider how adult friendships might impact physical health in ways similar to but also distinct from romantic partners. Utilizing this specific model, we identify features of friendships—the size and structure of friendship networks, the norms that define friendships, and the levels of interdependence in friendships—and discuss how each feature can amplify or blunt the strengths and strains afforded by friends, including their impact on health. Finally, we provide a roadmap and identify priorities to advance research on friendships and physical health.