Resilience as a Mediator in a Web-Based Intervention (MINDxYOU) to Reduce Stress Among Health Care Professionals: Stepped-Wedge Cluster Randomized Trial.

Background: The mechanisms through which mindfulness and third wave-based digital programs exert their effects on stress reduction remain poorly understood. Identifying these mediators is essential to optimize their implementation, particularly in health care settings. This approach is particularly relevant for health care professionals, who are constantly exposed to high levels of emotional demands, work overload, and risk of burnout, especially in the aftermath of the COVID-19 pandemic. Despite the growing need for scalable and accessible mental health support in this population, such digital programs remain scarce and underused. Objective: The primary aim of this study was to analyze the psychological mechanisms through which the MINDxYOU online program may contribute to stress reduction among health care professionals, focusing on a mediation model. Specifically, we explored if variables such as resilience and facets of mindfulness, compassion, and acceptance mediated the effects of the intervention on perceived stress. Methods: In a stepped-wedge cluster randomized design, 357 health professionals from health centers in Aragon and Málaga, Spain, were recruited. They were divided into 6 clusters, 3 per region, and randomly assigned to one of the 3 sequences, each starting with a control phase and then transitioning to the intervention phase (the MINDxYOU program) after 8, 16, or 24 weeks. This self-guided, web-based program, designed to be completed over 8 weeks, included weekly contact (via WhatsApp, call, or email) from the research team to promote adherence. Participants were assessed on the web every 8 weeks for 5 assessments. Perceived stress was the study's primary outcome, with additional measures of clinical factors (anxiety, depression, and somatization) and process variables (resilience, mindfulness, compassion, and acceptance). Mediation models using mixed-effects regressions and bootstrap resampling (1000 iterations) were applied to analyze the direct and indirect effects of the treatment on psychological outcomes. Results: Resilience emerged as the most consistent and significant mediator, exerting a relevant indirect effect on reducing stress (β=-1.41; P=.02), anxiety (β=-0.88; P=.03), and depression (β=-0.97; P=.01), even in multivariate models. Mindfulness facets such as observing, describing, and nonreacting also showed significant, albeit less consistent, mediating effects. In contrast, compassion and acceptance were weakly associated and did not play a significant mediating role. Conclusions: These results demonstrate resilience as the key psychological mediator. Strengthening resilience through online interventions appears to be a crucial pathway for reducing stress and emotional symptoms in this population. Specific mindfulness skills may also contribute to the intervention's therapeutic effect, although with less robust evidence.