Effects of Positive Psychology Interventions on Inflammatory Biomarkers and Cortisol: A Systematic Review and Meta-Analysis

Abstract There is growing interest in how well-being-enhancing activities influence stress and health. Positive psychology interventions (PPIs) foster such activities, but evidence regarding their physiological effects remains fragmented. This review aimed to examine the effects of PPIs on two physiological indicators of stress via a systematic literature review and meta-analysis. We included randomized controlled trials (RCTs) assessing the effects of PPIs on inflammatory biomarkers and/or cortisol in adult clinical and non-clinical populations. Searches were conducted in MEDLINE, Embase, PsycINFO, Epistemonikos, and clinical trial registries (from January 2000 to June 2023). Two reviewers independently screened studies, extracted data, and assessed risk of bias. Random-effects meta-analyses using robust variance estimation accounted for statistical dependencies. Effects were reported as Cohen’s d with 95% confidence intervals (CIs) and heterogeneity as prediction intervals (PIs). Twenty-five RCTs ( N = 1,641) were included. Common PPIs included music, nature exposure, gratitude, optimism, kindness, and meaning-focused activities. The overall effect was d = 0.39 (95% CI: 0.16, 0.62). The effect estimates were significant for inflammatory biomarkers ( d = 0.46, 95% CI: 0.02, 0.89), but not for cortisol ( d = 0.30, 95% CI: − 0.10, 0.71). A significant effect was observed in clinical groups ( d = 0.61, 95% CI: 0.17, 1.04); the effect in non-clinical groups was non-significant ( d = 0.23, 95% CI: − 0.01, 0.79). High heterogeneity and risk of bias warrant cautious interpretation. These findings suggest that PPIs may reduce inflammatory biomarkers. The clinical relevance of these effects remains uncertain and warrants further investigation, particularly in relation to long-term outcomes. Registration : The study protocol was registered with PROSPERO (CRD42023438736).