Biological Age vs. Chronological Age

Investigating the science and hype of biological age tests

- BY LAUREN J. YOUNG

HOW OLD ARE YOU REALLY? 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 have made in the science of aging,” says Eric Topol, a cardiologist and genomics professor at Scripps Research in La Jolla, Calif. “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 newest 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 of measuring it. Improved biological timekeeping can give 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 current and future health.

An edited transcript of the interview follows.

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

This research was really 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 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—a methyl-group molecule attaches to specific nucleotides of DNA. I kind of liken it to the body rusting out. Essentially you're getting marks at specific parts of the genome that track with aging in humans and every other species of mammal.