Study analyzes impact of blood cell composition on DNA methylation age and age acceleration estimates

A large-scale study published in Genome Medicine reports that up to 53% of the variation in DNA methylation age is driven by blood cell counts, showing that epigenetic clocks reflect distinct biological processes and highlighting the necessity of correcting for cell-type composition in longevity trials.

Researchers evaluated the contribution of blood cell composition to DNA methylation age (DNAmAge) and age acceleration (AgeAccel) across six first- and second-generation epigenetic clocks in 4,058 samples.

The study developed a principal component analysis (PCA) method robust to collinearity in blood cell counts to examine the biological drivers of these epigenetic measures.

Up to 53% of the variation in DNAmAge was attributed to blood cell counts, with a strong contribution from the balance between naïve and memory T cells.

Associations between AgeAccel and cell counts were weaker, explaining up to 21% of the variance, and for second-generation clocks, primarily involved neutrophils.

The study tested the influence of cell composition on the association between AgeAccel and 176 incident health outcomes in 18,859 individuals, finding that cell composition significantly but modestly attenuated these associations.

The finding that DNAmAge is heavily driven by blood cell counts suggests that changes in this metric may reflect shifts in the immune cell profile rather than cell-intrinsic epigenetic changes.

The distinct associations of DNAmAge and AgeAccel with cell composition indicate that they reflect different underlying biological processes, meaning they cannot be treated as interchangeable measures of biological age.

Because the cell-composition-related variance in AgeAccel has only a minor contribution to its association with mortality and incident disease, the predictive power of AgeAccel remains clinically valuable and largely independent of simple blood count fluctuations.

Developers of longevity therapeutics using epigenetic clocks as surrogate endpoints will need to integrate detailed blood cell profiling (such as flow cytometry or advanced epigenetic deconvolution) to validate that their candidates achieve true cellular rejuvenation.

Biomarker companies and diagnostic developers may face increased demand for second-generation clocks or multi-omic clocks that are less sensitive to confounding immune cell shifts, or for platforms that natively incorporate cell-count correction algorithms.

The adoption of the study's collinearity-robust PCA method by other academic and commercial teams analyzing epigenetic clock data in ongoing clinical trials.

Regulatory feedback from agencies like the FDA regarding the validated use of epigenetic clocks as biomarkers, particularly concerning how trials control for immune system remodeling during therapy.