Measuring your biological age with a saliva test? Here's how reliable that actually is
More and more people are having their "biological age" determined through commercial tests -- a cheek swab here, a drop of blood there. The results promise insight into how fast you are really aging. But what does that number actually tell you, and how solid is the science behind it?
The popularity of biological age tests is easy to understand. Chronological age -- the number of years you have lived -- is a poor predictor of how someone is doing on the inside. Two sixty-year-olds can look completely different biologically: one has the heart, blood vessels and immune system of a fifty-year-old, the other of a seventy-year-old. If aging is the single biggest risk factor for virtually every serious disease, then an accurate measurement of that aging process would be enormously valuable.
The most widely used method is the epigenetic clock: an algorithm that looks at methylation patterns on DNA. Those patterns change in predictable ways as we age, and the degree to which they deviate from the expected pattern is expressed as a "biological age." Well-known versions include the Horvath clock and the newer GrimAge and DunedinPACE.
The gap between the lab and clinical practice
The problem is that these clocks were developed and validated in specific populations, under specific conditions, using carefully controlled samples. Commercial tests ask consumers to mail in a cheek swab themselves or dry a drop of blood on paper -- methods that are sensitive to variation in sample collection, transport, temperature and processing time. Small technical differences can produce measurably different results.
On top of that, epigenetic clocks measure just one dimension of a multifaceted process. Aging happens simultaneously at the level of chromosomes, mitochondria, proteins, metabolites, the immune system and more. A methylation profile captures only part of that complexity. Two people with identical clock scores can have very different health profiles.
What that number does and does not tell you
The authors of the analysis on Lifespan.io are not opposed to biological age measurement in principle -- they caution against selling a certainty that science cannot yet deliver. The clocks are statistically interesting at the group level and useful as a research tool. But as a personal diagnostic instrument, especially in a direct-to-consumer context, their predictive value for any given individual remains uncertain.
The comparison with horoscopes is provocative but not entirely unfair. Both offer a narrative that sounds compelling and is difficult for the user to disprove. The difference is that the biological age industry uses scientific language, which raises expectations and deepens the disappointment when a test fails to deliver on its promises.