L-deprenyl extends lifespan across mammalian species: A meta-analysis of 22 longevity experiments

Identifying interventions that reproducibly extend lifespan is a central aim in geroscience, with hopes of translating these findings to enhance the health and longevity of older adults. L-deprenyl, an FDA approved medication, has been investigated for its role in aging for over three decades. To evaluate the effect of L-deprenyl on lifespan in mammals we performed a random-effects meta-analysis on 22 rodent lifespan experiments. The results indicate L-deprenyl significantly increases average lifespan with moderate effect size (SMD = 0.6773, p = 0.0002). We identified no significant evidence of publication bias in the examined studies, but did observe substantial heterogeneity. Accounting for experimental factors revealed significant effects of dose (p = 0.0233) and age at initiation (p < 0.0001), with higher doses and older age associated with larger effects. Assessment of treatment effects by mean lifespan of controls suggests short-lived controls are not responsible for the observed effects. In addition to the meta-analysis, we reanalyzed a dog survival study by Ruehl et al. When accounting for age at enrollment and sex, the study no longer displayed a significant effect on survival, though power was limited by small sample size. Together, this analysis of 23 L-deprenyl lifespan experiments spans 27 years of research in 6 countries, 8 strains of rodents, 4 species, 6 doses, and 2 delivery methods, providing some of the most comprehensive data supporting the effect of a compound on lifespan in mammals. Future clinical studies examining L-deprenyls effects on health outcomes in older adults will be critical to determine the translatability of these findings.