You have two ages. One is printed on your driver’s license. The other is written in your cells, and nobody hands you a card with it.

The first one is easy. Count the birthdays. The second one is harder to pin down, and it’s the one that decides how the next few decades go.

CNN ran a story with a headline I still like: “You have two ages.” It featured a Yale scientist named Morgan Levine, who had just built a better way to measure the second one.

Why the first clock wasn’t enough

As I wrote in the last post, the first epigenetic clock was trained to guess your birthday. It did that well. But two people can share a birthday and not share a future. That gap between birthday and biology is the reason I got into this work.

Levine’s team changed the question. Instead of training DNA to guess a person’s age, they trained it to read a person’s health.

They started with nine ordinary values from a routine blood panel. Blood sugar, a marker of inflammation, kidney function, white blood cell counts and a few others. Combined with age, those nine numbers predicted who died over more than twenty years of follow-up in a large national health survey.

Then they found 513 spots on the DNA whose methylation tracks that combined number. The result is a clock called PhenoAge. It reads your biology, not your birthday.

What it found

People whose DNA read older than their years died sooner. Each extra year on the clock carried about a 4.5 percent higher risk of death, after accounting for actual age.

Spread that across a population and the gaps get big. Among 50-year-olds, the fastest-aging 5 percent had a predicted median life expectancy of about 81. The slowest-aging 5 percent: about 86.

Same birthday. Five years apart.

The clock also lined up with how people live. People who exercised more, ate more fruits and vegetables, and had more education and income tended to read younger.

Age versus speed

PhenoAge tells you where you are. A different team asked a different question: how fast are you going?

They followed about 1,000 people in Dunedin, New Zealand, all born within the same year in the early 1970s. At ages 26, 32, 38 and 45, researchers measured 19 markers of how well each body was holding up. Heart, lungs, kidneys, liver, metabolism, immune system, even teeth and gums.

Then they tracked how fast each person’s numbers declined. Some people aged about one biological year per calendar year. Some aged less than half that fast. Some aged more than twice as fast. Same birth year. Very different trips.

The team trained a DNA test, called DunedinPACE, to read that speed from a single sample. A score of 1.0 means one year of biological aging per year on the calendar. A score of 1.2 means you’re aging 20 percent faster than average. In older adults, faster scores went with more chronic disease, more disability and earlier death.

Think of a car’s odometer and its speedometer. One tells you how far you’ve come. The other tells you how fast you’re using up the road ahead. I care more about the speedometer, because that’s the one I can still change.

Can you move it?

Here is the result that got my attention. In a two-year trial, 220 healthy adults were assigned either their normal diet or a 25 percent cut in calories. The calorie-cutting group’s pace of aging slowed by 2 to 3 percent.

That sounds small. Other studies suggest a slowdown that size could mean a 10 to 15 percent lower risk of death. That’s about what you would expect from quitting smoking.

Now the honest part. The same trial found no change on two other well-known clocks. Different clocks measure different things, and they don’t always agree. And cutting a quarter of your calories for two years is not for everyone. The researchers said so themselves.

What “biologically younger” means

I’ve had my biological age measured, and I liked the number. I also know what it is and what it isn’t.

It is a risk signal. It tells you whether your body is wearing out faster or slower than average for someone your age, based on patterns seen across thousands of people.

It is not a diagnosis. It doesn’t tell you which disease is coming or when. One test on one day is one reading. Different clocks can give the same person different numbers, so a score only means something next to the clock that produced it.

And it’s not a report card on your character. Some of what speeds up aging is out of your hands. The Dunedin researchers found faster aging in young adults with histories of poverty and victimization. Some of it is yours to change.

That’s why I like the idea of two ages. The first one only goes up. The second one responds to how you live.

The next question is the hard one. If your DNA says you’re aging fast, what does that mean for how long you’ll live? That’s the subject of the next post.

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.