The importance of baseline health in linking life purpose to longevity

The well-established inverse relation between purpose in life and mortality risk is widely interpreted in the literature as evidence that higher purpose causes greater longevity. This study assesses the role of baseline health in linking purpose and longevity. Based on a prospective cohort sample of 5,953 US adults aged ≥ 50 drawn from the Health and Retirement Study (2006-2018), we replicate a recent high-quality study that documents the correlation between purpose and longevity and then examine the sensitivity of the results to varying the amount of baseline health measurement error and limiting the sample to individuals with more homogeneous levels of baseline health. The relation between life purpose and longevity strongly attenuates when using more robust measures of baseline health and excluding individuals who are already seriously ill. For instance, in a model that uses the coarse measures of baseline health typically used in this literature, individuals with low purpose exhibit a hazard ratio for the subsequent 4-year period of 2.59 (95% CI = 1.43, 4.68). Once adjusting for more robust objective measures of baseline health, the hazard ratio falls to 1.77 (95% CI = 0.97, 3.22). After adjusting for objective measures of baseline health and excluding already ill individuals, the associated hazard ratio falls to 1.20 (95% CI = 0.66, 2.20) for survival over years 5-8 and 0.75 (95% CI = 0.42, 1.32) for survival over years 9-12. The results suggest that baseline health confounding or mediation explains much of the apparent relation between life purpose and longevity, and that the strong associations reported in the literature may largely reflect inadequate measurement of baseline health rather than a causal effect of purpose on longevity.