Biological Age Tests: What Your DNA Age Really Means
– 1 min read
A 55-year-old receives a longevity test reporting a “DNA age” of 61. The six-year difference looks precise. But what does it actually measure?
New research from Leiden University Medical Center (LUMC), published in Genome Medicine on 2 October 2026, suggests that the answer is more complicated than the language used by commercial biological-age tests implies.
Biological Age Tests: What They Actually Measure
Epigenetic age tests analyse chemical markers on DNA, particularly DNA methylation, rather than changes to the DNA sequence itself. These patterns are processed through mathematical models known as epigenetic clocks to estimate DNA methylation age.
LUMC researchers examined six established epigenetic clocks using blood samples from 4,058 people. They found that blood-cell composition accounted for up to 53% of the variation in DNA methylation age. The strongest relationships involved the balance between naïve and memory T cells.
Why DNA Age Is Not Your Whole-Body Age
The distinction matters. A biological age test may produce a single number, but that number does not mean that every tissue, organ or physiological system in the body is ageing at the same rate.
The study also found differences between DNA methylation age and age acceleration—the difference between predicted and chronological age. For age acceleration, blood-cell composition explained a smaller proportion of variation, up to 21%, with second-generation clocks particularly associated with neutrophils.
The researchers did not conclude that epigenetic clocks are useless. Rather, their findings suggest that DNAmAge and AgeAccel reflect partly different biological processes.
What to Ask Before Taking a Longevity Test
Before paying for a biological age test, ask which clock is being used, what biological measure it actually estimates, what sample is analysed, and whether the result has been validated for a specific health outcome.
A number such as “61” may be informative. It should not, however, be read as a literal age for the entire body.
