In the realm of epigenetics, the concept of biological age has gained significant attention, particularly through the use of epigenetic clocks. These clocks, which estimate biological age based on DNA methylation patterns, have been widely applied as biomarkers. However, the biological mechanisms underlying these clocks remain largely unclear. This study, published in Genome Medicine, delves into the role of blood cell composition in influencing DNA methylation age and age acceleration.
What this study does not show
While the study highlights the influence of blood cell composition on DNA methylation age, it does not establish a direct causal relationship between these factors and specific health outcomes.
The researchers began by developing a principal component analysis (PCA) method that effectively addresses the collinearity issues commonly found in blood cell count data. This innovative approach allowed for a more nuanced understanding of how variations in blood cell types contribute to the estimation of biological age.
In their analysis, the authors examined a substantial dataset comprising 4,058 samples. They quantified the contribution of various blood cell types to DNA methylation age and age acceleration, using six different epigenetic clocks. Notably, the study found that up to 53% of the variation in DNA methylation age could be attributed to blood cell counts, with a significant impact from the balance between naïve and memory T cells.
In contrast, the association between age acceleration and blood cell counts was weaker, accounting for up to 21% of the variance. For the second-generation epigenetic clocks, neutrophils emerged as the primary cell type influencing this relationship. To validate their findings, the researchers employed artificial cell mixtures, further supporting the role of cell composition in shaping epigenetic clock outcomes.
Furthermore, the study explored the implications of blood cell composition on the relationship between age acceleration and health outcomes. The authors investigated 176 incident health outcomes in a larger cohort of 18,859 individuals. They discovered that cell composition significantly attenuated the association between age acceleration and these health outcomes, although the effect was modest.
In conclusion, 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. Interestingly, while blood cell composition plays a role in shaping these epigenetic measures, its contribution to the association with mortality and incident disease outcomes appears to be minor.
Evidence scorecard
- Analytic validity: Established
- Clinical validity: Not established
- Clinical utility: Not established
This evidence is derived from primary research involving human participants.