A fox in the henhouse: the influence of lifespan on the study of health and healthspan

Abstract

Modern aging biology aims to understand how health and morbidity evolve over an individual’s life. To conceptualize health and “healthspan” in different ways that may be useful for biological or sociological study, several common analyses quantify lifetime health using statistics that combine measures of health and lifespan. While such efforts appear reasonable, we argue that such statistics confuse what types of processes contribute to health and lifespan; and, in fact, they risk circular reasoning by treating as an assumption what is in fact a very specific hypothesis: that lifespan and healthspan are tightly correlated. While this hypothesis is not impossible a priori, it remains a matter of active debate. Such hypotheses must not be unwittingly smuggled into the literature as hidden assumptions of specific analytic techniques. Consequently, we caution against generally quantifying lifetime health by any metric that combines both healthspan and argue that investigators should not mix longevity statistics with health measurements.