Most people believe their lifespan is written in their genes. Look at your parents, the thinking goes, and you know what you’re getting.

I used to believe a version of that. In my book I wrote that genetics explains 20 to 30 percent of who we become. Then researchers studied family trees covering more than 400 million people and concluded that the heritability of lifespan is likely no more than seven percent. Whatever the exact number turns out to be, the direction is clear. Most of what decides how long you live is not in the code you were born with.

So what is it?

The blueprint and the builder

Every one of your roughly 30 trillion cells carries the same DNA. A brain cell and a skin cell hold identical instructions. What makes them different is which instructions get read.

That is epigenetics. “Epi” means on top of. Sitting on top of your DNA is a layer of chemical switches that turns genes on and off. The best understood of those switches is DNA methylation: small chemical tags at specific spots along the genome, called CpG sites, that tend to keep a gene quiet. Your genome has about 28 million of those spots.

Think of your DNA as sheet music. Every cell has the entire score. Methylation is the conductor, deciding which parts get played, how loud and for how long.

The music changes

Here is what changed how I think about aging. Methylation is not fixed at birth. It shifts across a lifetime, and it responds to how we live.

Identical twins make the case better than any argument. They start life with the same DNA. In one study of 40 pairs of identical twins, researchers found that young twins had nearly identical methylation patterns, but the patterns drifted apart with age. Among twins older than 28, more than 60 percent of pairs showed significant differences. The twins who had spent the most years living apart showed the biggest gaps.

Same genes. Different lives. Different gene activity.

Some of what writes on our DNA we can’t control: chance, illness, where and how we grew up. Some of it we can. Smoking leaves one of the clearest methylation fingerprints scientists have found. Diet, exercise, sleep, stress and alcohol all show up in the research too, some more strongly than others.

Why it matters for a long life

If your lifespan were mostly genetic, there would be little point in planning. You would look at your family tree and make a guess. The evidence says the opposite. The choices you make show up in your biology, day after day, decade after decade.

That doesn’t mean there is one right way to live. I’m skeptical of anyone selling a single formula. Eat well, move more, sleep, stay connected: everyone knows the basics. For me it’s daily journaling, strength training, eating clean and the sauna three or four days a week. I know it’s good for me. Your version will look different.

What matters is the shift in thinking. Your DNA is the starting point, not the verdict.

And if methylation changes with age in a predictable way, a curious person might ask whether you could read someone’s age from it. A biostatistician at UCLA asked exactly that question. His answer became the epigenetic clock, and it’s the subject of the next post in this series.

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.