Metformin has heterogeneous effects on model organism lifespans and is beneficial when started at an early age in Caenorhabditis elegans: A systematic review and meta-analysis

There is growing interest in the use of metformin to extend lifespan and prevent the onset of age-related disorders in non-diabetic individuals. The impact of metformin on lifespan and aging has been studied in several model organisms, with varying effects. We conducted a systematic review of studies that performed laboratory experiments investigating the effect of metformin on overall lifespan in healthy Mus musculus mice and in Caenorhabditis elegans nematodes. Lifespan results for mice and nematodes were analyzed in separate meta-analyses, and there was a significant amount of heterogeneity across experiments within each species. We found that metformin was not significantly associated with an overall lifespan-prolonging effect in either mice or nematodes. For nematodes, however, there was a lifespan-prolonging effect in experiments using live OP50 Escherichia coli as a food source, an effect that was larger when metformin was started earlier in life. Our work highlights the importance of testing compounds in a diversity of model organisms. Moreover, in all species, including humans, it may be necessary to study the effect of metformin on aging in both younger and older cohorts.