Are DNA methylation tests for biological age worth the money?

DNAm PhenoAge, a widely used epigenetic clock, predicts mortality, cancer, physical functioning and Alzheimer's disease better than earlier-generation clocks. Multiple population studies show an independent association between an accelerated epigenetic pace and higher mortality and chronic disease. That is scientifically interesting, but these are purely statistical associations. Whether a higher score is also a cause of health problems, or merely a by-product, has not been established.

The technology can capture biologically relevant signals. For example, the skin & blood clock detects accelerated ageing in a rare disease in which people age extremely rapidly, while older clocks missed that signal. A model combining two types of methylation measures achieves a margin of error of approximately 2.5 years in an Italian group of 194 individuals, but the researchers themselves note that validation in other populations is needed. These are research findings, not evidence that commercial tests perform to the same standard.

That is precisely where a major problem lies. A review identified that many methylation models suffer from methodological shortcomings, such as data leakage during training and groups that are too small or one-sided. As a result they overestimate their own performance, and that overestimation flows directly into a commercial product. Moreover, a clock that works well in adults cannot simply be applied to children or other groups: a clock developed specifically for children achieves a median error of just 0.35 years, while standard clocks perform far worse in children.

What does your test result actually tell you? The fact that your biological age turns out higher or lower than your chronological age is a population-level figure. It does not mean that your personal risk of disease increases or decreases proportionally. There are also no proven intervention studies demonstrating that you can improve your epigenetic age score in a way that also benefits your health. In the development of a new index for cellular ageing, several authors had furthermore filed patents on the technology: weigh findings from that particular study with some caution.