Imagine two people. They are both women, they are both 46 years old, and they both work in engineering. They even live in the same city.
Despite these similarities, the women’s lives and lifestyles are very different. One of them is exacting about her health. She eats well, exercises, spends lots of time with friends, and sleeps eight hours every night. She’s also lucky to have parents and grandparents who all lived long lives free of illness.
Meanwhile, her counterpart smokes heavily, lives on fast food, and hasn’t exercised since childhood. She also has a family history of early death and chronic disease.
You don’t have to be a health expert to recognize that these two women are not at the same risk for disease and untimely death. And this is where the concept of biological age comes into play.
“The question that’s most important to people is not ‘How old am I?’ but ‘How long have I got to live?’ and biological age attempts to answer that,” says John Beard, PhD, professor and director of the International Longevity Center at Columbia University in New York City.
Complex and dynamic biological changes underpin aging and an individual’s risk for disease and functional declines, Dr. Beard says. “Biological age is about identifying the underlying changes driving all of that.”
RELATED: 10 Steps to Health, Happy Aging
What Is Chronological Age vs. Biological Age?
The distinction between the two is straightforward. One is a measure of time, and the other is a measure of health, disease risk, and functioning.
“While chronological age is a measure of the years a person has been alive, biological age is an attempt to estimate an individual’s physiologic age in order to more accurately reflect their functionality and risk of age-related diseases or death,” says Alexandra White, PhD, a cancer epidemiologist at the National Institute of Environmental Health Sciences in Durham, North Carolina.
RELATED: 8 Tips to Keep Your Brain Sharp and Health as You Age
How Is Biological Age Measured?
This is where things get tricky.
“People have tried to measure biological age by looking at various internal biomarkers or physical manifestations of aging, and there are a lot of them,” says Michal Jazwinski, PhD, director of the Tulane University Center for Aging in New Orleans.
For example, some researchers have attempted to assess a person’s biological age based in part on cellular or blood biomarkers, according to a mini-review article published in Frontiers in Genetics in March 2019. There are also physical or functional things experts can measure — like lung capacity, grip strength, and nerve conductance — that some researchers use to gauge biological age, says Dr. Jazwinski.
“If you look at just one of these biomarkers, it probably won’t tell you much,” he explains. “So what a lot of people have tried to do is to take a bunch of these — a dozen or more — and generate an algorithm that combines them into one measure of biological age.”
There are also several DNA-based measures of biological age that are now being studied either alone or in combination with other biomarkers.
For example, a lot of expert attention has been paid to the length of telomeres, which are caps on the ends of chromosomes that shorten as a person ages, according to a review article published in Frontiers in Genetics in January 2021.
Other research has focused on DNA methylation, which is a chemical modification that causes some genes to be switched on or off, according to the National Human Genome Research Institute.
DNA methylation-based biomarkers are often referred to as “epigenetic age” or “epigenetic clocks,” because they are strong estimators of the chronological age of an individual, and may also help reveal biological age, according to a study published in Aging in September 2016.
As of right now, there is no “agreed-upon standard” when it comes to measuring biological age, Jazwinski says.
Beard agrees. “There are all sorts of people working in different fields — whether telomere length or inflammatory markers — and this work is increasing our understanding and giving us a more nuanced picture of health and aging,” he says. “But we’re a ways away from identifying some test that tells you everything you want to know.”
As for the online companies or calculators that offer biological age estimates, at this point, experts say their validity is shaky.
“There are various companies that offer kits to measure epigenetic or biological age,” says Steve Horvath, PhD, a professor of human genetics and biostatistics at UCLA in Los Angeles. “My recommendation is to use epigenetic testing for scientific research only at this point.”
Is Biological Age a Good Indicator of Health?
If you want to get a helpful assessment of your health status, Dr. Horvath says visiting a doctor and having a thorough exam — weight, blood pressure, full blood panel (cholesterol, blood sugar) — is still the way to go.
“Tests that are commercially available should not be taken to be more meaningful than a doctor’s assessment,” he says. “Getting an epigenetic test may give an individual the wrong answer and cause that person to become overly worried or stressed.”
Could Knowing Your Biological Age Help You Live Longer?
The moonshot hope is that, someday, biological aging breakthroughs could lead to the development of interventions that stop or even roll back the aging process — either in a specific part of the body or throughout it.
Already, there are researchers looking into various kinds of treatments to reverse epigenetic aging, says Horvath. He mentions research efforts targeting the thalamus, as well as nerve cells in the eye. “No treatment has been approved yet for rejuvenating humans,” he adds. But hopefully those are coming.
Experts also say that as measurements of biological aging become more refined, they should help doctors and other care providers offer more effective individualized advice and treatments for their patients.
Beard offers an example. “When it comes to physical activity, we still give people pretty generic advice that may not suit everybody,” he says. Accurate biological-age estimates could help researchers better assess the benefits of different forms of exercise, and so help doctors give more useful and specific guidance — more walking for this patient, more high-intensity interval training for that one.
“I think we’re going to go through a transformative period where rather than looking at people as batches of diseases, we’re going to look more holistically at the underlying drivers of aging and illness,” Beard says.
The concept of biological aging will underpin that transformation, he says. But medical science still has a lot of work to do to take us there.