The impact of short-lived controls on the interpretation of lifespan experiments and progress in geroscience - Through the lens of the "900-day rule".

Although lifespan extension remains the gold standard for assessing interventions proposed to impact the biology of aging, there are important limitations to this approach. Our reanalysis of lifespan studies from multiple sources suggests that short lifespans in the control group exaggerate the relative efficacy of putative longevity interventions. Results may be exaggerated due to statistical effects (e.g. regression to the mean) or other factors. Moreover, due to the high cost and long timeframes of mouse studies, it is rare that a particular longevity intervention will be independently replicated by multiple groups. To facilitate identification of successful interventions, we propose an alternative approach particularly suitable for well-characterized inbred and HET3 mice. In our opinion, the level of confidence we can have in an intervention is proportional to the degree of lifespan extension above the strain- and species-specific upper limit of lifespan, which we can estimate from comparison to historical controls. In the absence of independent replication, a putative mouse longevity intervention should only be considered with high confidence when control median lifespans are close to 900 days or if the final lifespan of the treated group is considerably above 900 days. Using this "900-day rule" we identified several candidate interventions from the literature that merit follow-up studies.