Epigenetic clocks, which serve as biomarkers of biological age, have gained significant attention in recent years. However, their biological underpinnings remain somewhat elusive. In this study, the authors investigate the role of blood cell composition in determining DNA methylation age and age acceleration.
What this study does not show
This research does not establish a direct causal relationship between blood cell composition and health outcomes, nor does it provide definitive conclusions about the clinical utility of DNA methylation age as a standalone predictor of health.
Evidence scorecard
- Analytic validity: Established
- Clinical validity: Partial
- Clinical utility: Not established
The study employs a robust principal component analysis (PCA) method to address the collinearity of blood cell counts. This approach allows for biologically meaningful insights into the relationship between cell composition and epigenetic clocks. The analysis is based on a substantial dataset of 4,058 samples, providing a solid foundation for the findings.
One of the key findings is that up to 53% of the variation in DNA methylation age can be attributed to blood cell counts, particularly the balance between naïve and memory T cells. This suggests that the composition of blood cells plays a significant role in influencing biological age as measured by DNA methylation.
In contrast, the association between age acceleration and cell counts is weaker, explaining up to 21% of the variance. Notably, for second-generation epigenetic clocks, neutrophils appear to be the primary cell type involved.
Furthermore, the study explores the impact of cell composition on the association between age acceleration and 176 incident health outcomes. While the results indicate that cell composition significantly attenuates this association, the effect is described as modest.
Overall, the findings suggest that DNA methylation age (DNAmAge) and age acceleration (AgeAccel) reflect different biological processes, as evidenced by their distinct associations with blood cell composition. Despite the significant contribution of cell counts to epigenetic clocks, the variation in age acceleration attributed to blood cell composition has only a minor impact on its association with mortality and incident disease outcomes.
Conclusion
This study highlights the intricate relationship between blood cell composition and epigenetic markers of aging. While it sheds light on the biological interpretations of DNA methylation age and age acceleration, further research is needed to fully understand the implications for health outcomes.