Give a lab a small tissue sample and no other information, and it can tell you roughly how old you are. Within a few years, most of the time.

Not from your skin or your hair or your X-rays. From your DNA.

The man who found the clock

Steve Horvath is a biostatistician at UCLA. He wanted to know whether the methylation marks on our DNA, the chemical switches I described in the last post, change with age in a way that is regular enough to measure.

He gathered about 8,000 samples from 82 existing data sets, covering 51 kinds of healthy tissue and cells, from blood to brain to liver. Then he looked for spots on the genome whose methylation rises or falls steadily with age. He found 353 of them that, read together, keep time.

In the test data, the clock’s estimates lined up with people’s real ages almost perfectly. The typical miss was 3.6 years. And it worked across tissues, which surprised a lot of scientists, because different organs were assumed to age on different schedules.

One result hinted at something deeper. Embryonic stem cells, and adult cells reprogrammed back into stem cells, read as close to zero. Reset the cell, and you reset the clock.

Why the misses matter

A typical miss of 3.6 years means some people read older than their birthday and some read younger. That gap is the most interesting thing the clock measures. Researchers call it age acceleration.

Horvath and others kept finding the same pattern. People whose DNA reads older than their calendar age tend to develop age-related disease sooner and die sooner, even after accounting for their actual age. Smokers tend to read older. People who exercise and eat well tend to read younger.

I’ve had mine measured. My biology came back about ten years younger than my birth certificate. I give the credit to habits I started decades ago. I can’t prove that’s the cause. I’d bet on it.

From one lab to everywhere

In 2014, Nature profiled Horvath as “The Clock-Watcher.” A copy of that profile landed on my desk and changed the direction of my career, a story I tell in another post. In 2017, the Paul G. Allen Frontiers Group named him an Allen Distinguished Investigator to push the clock research further. Today, epigenetic clocks are standard tools in aging research and are being used to test whether drugs, diets and supplements slow biological aging.

What the first clock can’t do

The first clock was built to predict calendar age, and it does that well. But predicting your birthday is not the same as measuring your health. Two 60-year-olds can have the same epigenetic age and very different futures.

So the next generation of clocks was trained on something more useful than birthdays: blood chemistry, disease and death. Those clocks are the subject of the next two posts. They are where the measurement starts to matter for how long, and how well, you live.

This is not medical advice.

Sources

Jon Sabes is a named inventor on U.S. Patent No. 11,817,214 and managing member of LongevityFP Technologies, LLC, which holds an exclusive license to FOXO Technologies’ epigenetics technology.