Epigenetic clocks are increasingly recognized as biomarkers of biological age, yet their biological foundations remain largely elusive. This study investigates the role of blood cell composition in influencing DNA methylation age and age acceleration, shedding light on their distinct biological interpretations.
What this study does not show
This study does not establish a direct causal relationship between blood cell composition and health outcomes, nor does it quantify the clinical implications of these findings.
Evidence scorecard
- Analytic validity: established
- Clinical validity: not established
- Clinical utility: not established
The research utilized a robust principal component analysis (PCA) method to address the collinearity of blood cell counts, allowing for biologically meaningful insights. The study analyzed 4,058 samples to quantify the contribution of cell composition to DNA methylation age and age acceleration, as estimated by six different epigenetic clocks. Notably, the findings revealed that up to 53% of the variation in DNA methylation age could be attributed to cell counts, particularly highlighting the balance between naïve and memory T cells.
In contrast, the associations between age acceleration and cell counts were weaker, explaining up to 21% of the variance, with neutrophils playing a significant role in 2nd-generation clocks. The study also validated the contribution of cell counts to epigenetic clocks through artificial cell mixtures.
Interestingly, the research found that cell composition significantly attenuated the association between age acceleration and 176 incident health outcomes, although the effect was modest. This suggests that while DNA methylation age and age acceleration are influenced by blood cell composition, they may reflect different biological processes.
Ultimately, the study concludes that the variation in age acceleration attributed to blood cell composition has only a minor contribution to its association with mortality and incident disease outcomes. This highlights the complexity of biological aging and the need for further research to unravel the underlying mechanisms.