LAUSR

Abstract Close others often serve as a source of support for our pursuit of personal goals. Although social psychological research indicates that individuals and relationships benefit when couple members provide each other with secure base support for personal goals, few studies have investigated the physiological bases of these types of support interactions. This study of married older adults examined support providers' cardiovascular challenge‐threat responses while they engaged in a laboratory social interaction about the most important goal that their partner (the target) wanted to make progress toward during the next year. Consistent with our hypothesis, support providers' cardiovascular challenge responses were positively associated with targets' ratings of their secure base support provision during the discussion. This study also used structural equation modeling to test a theoretical model of support providers' cardiovascular challenge responses as a physiological basis of secure base support provision that promotes targets' goal progress and thriving over time. Consistent with our theory, support providers' cardiovascular challenge responses were positively associated with targets' goal progress at Year 2 follow‐up. In turn, targets' goal progress at Year 2 predicted increases in targets' overall thriving from Year 1 to Year 3. This investigation provides novel evidence for attachment theory's assertion that biobehavioral caregiving system activation facilitates the provision of secure base support that promotes close others' goal progress and thriving over time. Results of this study also contribute to recent evidence that cardiovascular challenge responses are associated with social behaviors during dyadic interactions.