How healthy is the healthspan concept?

Geroscience, the study of biological mechanisms of aging, has seen a surge in interest in the concept of healthspan since the year 2000. The number of publications referencing "healthspan" has dramatically increased, yet a consensus definition and validated measurement methods are lacking. The paper questions the widespread use of phrases like "increases healthspan" without established metrics. The author acknowledges their own past contribution to this imprecise usage. A common definition of healthspan is the duration of life spent in good health, free from age-related diseases and disabilities. This definition, while appealing due to its quantitative nature, suffers from several significant flaws. The primary issue is the subjectivity of "good health." Individual perceptions of health vary greatly, even among those with the same medical conditions. Furthermore, health is not a binary state (good or bad) but a continuous variable that dynamically changes throughout life. Determining the endpoint of healthspan is also problematic, as the number and severity of diseases required to mark its end remain unclear. The definition also struggles to account for health problems unrelated to aging, such as childhood disorders.

The paper reviews existing literature on healthspan, highlighting the increasing number of publications using the term without a clear operational definition. It cites studies claiming to increase healthspan based on limited measurements of age-related phenotypes. The author points out that even studies showing broad improvements in age-related declines (e.g., rapamycin treatment in mice) lack robust methods to assess healthspan extension statistically. The controversies surrounding rapamycin's effects in mice and the impact of DAF-2 mutation in C. elegans are partly attributed to imprecise healthspan definitions. This literature review underscores the need for a more standardized approach to healthspan research.

The paper uses a conceptual analysis approach to examine the limitations of the current healthspan concept. It doesn't employ empirical data collection or statistical analysis. Instead, it critically evaluates existing definitions and their implications for research. The author proposes alternative approaches, such as a "healthspan index" similar to frailty indices or geropathology platforms, which could incorporate multiple aspects of health (physical, emotional, psychological). The paper suggests calculating the area under a health metric curve over a lifetime as a potential single healthspan metric for individuals. This would provide a more comprehensive assessment than solely relying on chronological time.

The paper's central finding is the lack of a standardized and validated method for measuring healthspan. The existing definition of healthspan is subjective, relying on the undefined concept of "good health" and struggling to account for the dynamic and continuous nature of health. The end point of healthspan is difficult to objectively define. Various attempts to quantify healthspan are critically examined and found to be insufficient for rigorous scientific comparisons. The author argues that without a robust and widely adopted metric, claims regarding healthspan improvements should be made with caution. Studies focusing on one or two age-related phenotypes are particularly problematic when making broad healthspan claims. The use of the area under the curve for a healthspan metric is suggested to allow for valid comparison of different interventions.

The absence of a reliable healthspan metric undermines the rigor of current geroscience research. The current state of affairs leads to confusion and may create a perception of less rigor compared to other scientific fields. While the concept of healthspan has proven useful in popularizing geroscience among the general public, this benefit does not justify the lack of precision in its scientific application. The author emphasizes the need for a comprehensive approach to assess health across multiple domains and ages before making claims about healthspan extension. The debate surrounding the effects of interventions like rapamycin in mice highlights the necessity for standardized measures. Until a robust healthspan metric exists, the paper cautions against the use of the term beyond a conceptual level.

The paper concludes that the current lack of standardized metrics for healthspan presents a significant challenge to the field of geroscience. It urges researchers to avoid using the term "healthspan" imprecisely in scientific publications until a comprehensive metric is established. The focus should shift towards developing and validating such metrics to ensure rigor and comparability in future research. Although the concept has value in public outreach, scientific rigor necessitates a more precise and measurable approach.

The paper primarily relies on a conceptual analysis and review of existing literature, rather than presenting original empirical data. It does not propose a specific, fully developed healthspan metric but highlights the need for such a metric to be created. The discussion is largely theoretical, focusing on the conceptual limitations rather than providing a practical solution for immediate implementation.