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How old are you really? Counting birthdays may be a common tally, but your “age” isn’t determined by time alone. New research increasingly shows the importance of considering chronological age as something very different from biological age, in which the body and its cells, tissues, and organs all have separate “clocks” that can tick at different speeds.

“Calculating biological age, I think, is core to the advances we’ve made in the science of aging,” says Eric Topol, a cardiologist and genomics professor at Scripps Research in California. “It’s a way you can tell if a person, organ, or any biological unit is at pace of aging—if it’s normal, abnormal, or supernormal.”

In his new book Super Agers: An Evidence-Based Approach to Longevity, Topol delves into the recent surge in public interest in biological aging and the accelerating quest to refine ways to measure it, giving a more precise picture of a person’s longevity prospects and of potential ailments that can be prevented or treated early. Scientific American spoke with Topol about the latest research in biological aging, factors that might speed it up or slow it down, and what it can tell us about our health.

How is biological age determined, and how has the research evolved?

The real beginning of this research started more than a decade ago by geneticist Steven Horvath with his “clock” [test], with which, basically using saliva, you could look at specific genetic markers in a genome and predict a person’s biological age. His clock is really known as an epigenetic clock, or methylation clock. As people age, DNA changes and gets methylated—this is when a methyl group [molecule] attaches to specific nucleotides of DNA. I kind of liken it to the body rusting out. Basically, you’re getting marks at specific parts of the genome that track with aging in humans and every other species of mammal.

In Horvath’s initial test, there clearly was a detection of both alignment with the person’s real age, or chronological age, and when it wasn’t matching up. In other words, if a person’s biological age was off by a few years from their real age, you’d wonder why that is.

Then what’s proliferated in the more than 10 years since has been all these other clocks: protein clocks, RNA clocks, immune system clocks—you name it. Using plasma proteins from a blood sample, we can also clock organs—whether it’s the heart, brain, liver, or kidney. So we have seen just enormous advances in these clocks, and they keep getting refined with added features. There’s a race to get the best clocks to predict survival.

What can biological age tests tell us clinically?

We can detect in an individual if something’s not right at different levels. For example, if your biological age is five years older than your real age, is there an organ that might be linked with that? Then you can use these clocks to see if lifestyle, prevention, or treatment can slow down the pace of aging and get it into alignment with your actual age.

The question is: When will doctors actually start using them? The medical community is very hard to change. So it hasn’t happened yet, but I believe it will eventually. Tests are also made available by commercial companies, but they can be very expensive. You can run an epigenetic test in a very simple way for $10 or $20, while some of these companies are charging $200.

I haven’t seen their publications to be able to say with confidence that they are doing things right, and the lack of standards from one company to the next is disconcerting. They don’t want to shock [customers by telling them] that they’re 10 years older than their real chronological age. Eventually, I believe, we’re going to have high-fidelity epigenetic clocks with no motivation for a provider to hold things back if a person’s data are really bad.

Why might someone biologically age “faster” or “slower” than their actual age?

If you had to pick one mechanism behind why biological age and chronological age are misaligned, it would most likely be because there are some genes that are either protective or linked with accelerated aging, but that’s such a small part of the story. Another root cause appears to be that our immune system gets weaker and less functional as we get older. In the average person, this starts around age 55 to 60. It drops its level of protection, or it gets dysregulated—off track—and it can have an untoward, hyperactive response. Now, when you have that happen, you start to see inflammation in the organs, such as in the arteries of the heart or the brain—it’s what I call “inflammaging.”

Obviously, our lifestyle also has a big impact—eating a really healthy diet that’s not proinflammatory and doesn’t have a lot of ultraprocessed foods or red meat. Good sleep health helps reduce inflammation. There’s only one thing that’s been definitively shown to slow the epigenetic aging process, and that’s exercise. I think these clocks ultimately are going to be very good incentives for people to adopt a healthy lifestyle. We can’t get everybody to do all these things that we know help them, but if they get their own data and they see something’s off track, the hope is that they’d [change their lifestyle]. That’s, of course, just one of the ways to prevent diseases. There are also drugs and other treatments.

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