Background: Characterizing the effects of physical activity (PA) and cardiorespiratory fitness (CRF) on mortality is challenging because the causal relationship between PA, CRF, and other cardiovascular risk factors is unclear. Methods: To better understand the effects of PA and CRF on mortality, we re-analyzed data from 42,373 participants in the Aerobics Center Longitudinal Study (ACLS) using a modified version of VanderWeele's four-way causal effect decomposition method. The method was applied to decompose the causal effects of PA and CRF on median time to death into parts reflecting mediation, interaction, mediated interaction, and neither interaction nor mediation. Results: We found that 67% of the effect of PA on mortality was mediated by CRF, while the effect of CRF was not significantly mediated by PA. The effects of both PA and CRF were mediated to a small extent by hypertension and diabetes. There were no meaningful interactions. Conclusions: Our findings strengthen the evidence that the benefit on mortality from PA is largely mediated by its effect on CRF, and support efforts to increase longevity by encouraging PA.
Bibliographical noteFunding Information:
The collection of the original data and analyses for the previously published paper (Lee et al. 2011) was funded by the National Institutes of Health grants AG06945 and HL62508, an unrestricted research grant from the Coca-Cola Company, the Korea NEST Foundation for the Next Generation Sports Talent, Spanish Ministry of Education (EX-2008-0641) and European Community Sixth RTD Framework Programme (Contract FOOD-CT-2005-007034).
The authors thank the Cooper Clinic physicians and technicians for collecting the baseline data, and staff at the Cooper Institute for data entry and data management.
© 2019 The Authors
- Cardiorespiratory fitness
- Causal effects
- Physical activity