A systematic literature search was conducted in five electronic databases and the ClinicalTrials.gov registry. Controlled trials of mindfulness-based stress reduction or mindfulness-based cognitive therapy programs for older adults measuring any physiological outcome were identified. The combined p-value analysis, following the Synthesis Without Meta-analysis reporting guidelines, was used for data synthesis. Based on 22 eligible studies, the synthesis shows a positive effect of MBIs on 43 physiological outcomes grouped by five stress-related systems, i.e., brain circuits and signalling (combined p-value < 0.001), the sympathetic-adrenomedullar axis (combined p-value = 0.004), the hypothalamus-pituitary-adrenal axis (combined p-value = 0.011), the immune system (combined p-value = 0.037), and gene expression and epigenetic mediators (combined p-value < 0.001). The file xls includes the data needed to replicate the findings.