A Systematic Cross-Comparison of Eight Longevity Interventions on Heart Rate Variability: Meta-Analysis and Custom Meta-Synthesis

Background. Eight interventions—aerobic exercise, meditation, HIIT, intermittent fasting, caloric restriction, cold exposure, heat therapy, and social connection—have meta-analytic support for longevity benefits, but lack a common-metric comparison. Methods. Effect sizes on heart rate variability (HRV) were aggregated from published meta-analyses (aerobic exercise, meditation) or custom mini-meta-analyses (HIIT, intermittent fasting, caloric restriction, heat therapy). Cold exposure and social connection were assessed via surrogate outcomes. Results. Aerobic exercise (d = 0.62, 95% CI 0.47–0.77) and meditation (d = 0.42, 95% CI 0.28–0.56) showed non-overlapping confidence intervals. Tier-2 interventions showed larger but less precise effects (d ≈ 1.0–1.2), likely inflated by small-study bias. Cold exposure (BAT activity, d = 0.66) and social connection (all-cause mortality, HR = 0.74) provided complementary evidence. Conclusion. Aerobic exercise and meditation produce distinguishable HRV effects, consistent with distinct autonomic mechanisms. A four-category classification framework is proposed. Tier-2 effects warrant confirmation in larger trials.