Why 60 isn’t the same for everyone?

I’m sure, like everyone else, you’ve looked at a celebrity turning 60 and thought, “Wow, they look great for their age!” and not just celebrities. Doesn’t it seem like some people wear their age differently to others? We know people age differently, and fresh research into epigenetic clocks might have revealed new information as to why 60 isn’t the same for everyone, and how we can measure the wear and tear on our bodies. But does the new testing measure up? What are “epigenetic clocks,” anyway? You’ve probably heard the idea: your chronological age is just how many years you’ve been alive. But your biological age, or how “worn” your body really is, may well be very different. That’s where epigenetic clocks come in. These tools look at markers on your DNA (specifically, DNA methylation) that tend to shift as we age, to estimate how “old” your tissues are biologically. In principle, that can help scientists, and maybe one day doctors, figure out whether you’re aging faster or slower than average. So far though, most of these clocks were built using blood samples. But saliva swabs or cheek-swabs (less invasive!) are gaining popularity, including among commercial “biological age tests.” So, the big question: do these clocks still work if you use mouth-based tissue instead of blood? Here’s what the new study tested. Researchers grabbed samples from 83 volunteers, aged between 9 and 70, collecting five different tissue types from each: Cheek-based (buccal) cells. Saliva. Dry blood spots. Buffy coat (a blood fraction rich in certain white blood cells). Peripheral blood mononuclear cells (PBMCs, which is also a blood fraction). In total, the researchers studied 284 separate tissue samples. Then they applied a range of commonly used epigenetic clocks to each, to see how much the “biological age” estimates bounced around, depending on what tissue was tested. And here’s what they found... Big discrepancies between the samples studied. For many participants, the age estimate from saliva or cheek-swab was wildly different from the age from their blood. In some cases, the difference was almost 30 years. That’s not a small error.  Low correlation across tissues. Even within the same person, the “biological age” from oral tissue often didn’t match the blood-based estimate, even after adjusting for technical factors like cell composition.  One clock marker stands out. Among all the clocks they tested, the one called “Skin and Blood” clock performed best. It gave relatively consistent age estimates across both blood- and oral-based tissues. It was the “least bad,” but even then, only relatively. So, what’s the bottom line here? It appears that using a clock designed for blood, on saliva or cheek cells, is risky and often gives misleading results. By now, you might be asking what does this mean, and why does it matter? Well... If a lab or a consumer test uses saliva or cheek swabs to estimate your biological age, the results could be seriously off. For scientists building “aging clocks,” these results underline a big limitation: you can’t assume one clock works for all tissue types. DNA methylation patterns differ across cell types.  So, for now, blood remains the gold standard if you care about accurate biological age. In short, the research shows tissue type matters a lot. As one of the study authors put it, if you want a valid reading, “the tissue used to measure someone’s biological age must match the tissue used when the clock was created.” So, what can you, as an everyday reader, take away from this research? Treat claims about biological age (especially from cheek-swabs or spit) with a healthy dose of skepticism. If you ever try a “biological age test,” ask: What tissue did they use? And: Which clock? For reliable comparisons (say, tracking your “age” over time), consistency matters. Always use the same tissue type and clock. Finally: remember this: biological age is only a proxy. It can be informative, but it’s not a crystal ball. So there you have it: a clear, no-nonsense look at what this new research means. The idea of measuring “biological age” is exciting. But science is rarely simple. And sometimes, like when you mix up tissue types, the results just don’t add up.

Yours in good health, Andrew Peloquin Editor-in-chief, The Longevity Journal