We all know how old we are. But the measure of years since when we were born, also called “chronological age,” is just one way to think about age. Epidemiologists, gerontologists, and geneticists also study “biological age” and the wide range of variables that affect it, as well as which populations are most at risk for accelerated aging, in an effort to better understand how to preserve our health for longer.
Intuitively, you might guess that biological age measures how old you are physically. That’s somewhat true—it’s a way to assess whether a person’s body, or even individual organs, are as healthy as those of others of the same age. For an individual in their 30s, a biological age of 50 means their biology more closely resembles someone 20 years their senior.
In research, the term “biological age” can mean slightly different things depending on how it’s measured, says Andrea La Croix, a professor of epidemiology at the University of California San Diego. You could measure walking ability, and see how fast and agile or slow and stiff a person is compared to others their age. Or you could measure something much more granular, like whether the inflammation levels in their body are as expected for how old they are. Simply put, biological age is a way to gauge how people compare to others with different health metrics, La Croix says.
Oftentimes when talking about biological age, researchers will also refer to “epigenetic age.” Epigenetics is the study of how genes turn on or off depending on an individual’s behaviors and environment. There are certain parts of our genome we want to keep off, and others we want to keep on, “but as we age, those distinctions become less pronounced,” says Steve Horvath. As a biogerontologist at Altos Labs, he developed the first epigenetic clock to look at which genes are active or not, and use that data to pretty accurately measure the age of specific organs and tissues in the human body. A higher-than-expected biological age means a person’s genes are activated in a way that deviates from what scientists would consider normal or expected for their chronological age.
What affects biological age?
The variables that determine biological aging overlap with the ones that influence health more generally. Smoking, obesity, and inflammation markers in your blood are all factors that causally increase your biological age, Horvath says; women who enter menopause earlier also have higher biological age.
There are social and environmental factors to consider too, says Jamaji Nwanaji-Enwerem, a physician and environmental health scientist at Emory University. He has analyzed how exposure to air pollutants, metals, and life stressors are associated with higher biological age. In one 2021 study, he and his team found that mothers in California who had adverse childhood experiences (like experiencing violence, abuse, or neglect, for example) were more likely to give birth to babies with slightly higher epigenetic ages. Another US-based study published in June found that people living in neighborhoods with more access to green spaces had biological ages that were on average 2.5 years younger than those with limited access. The authors found further disparities when also looking at race, sex, and socioeconomic status.
There is one caveat to biological age to consider, Nwanaji-Enwerem notes. Assessing someone’s biological age, regardless of what variable you’re looking at, means jotting down their stats and comparing them to the rest of the population on a bell curve. But more research is needed to know exactly how biological age translates to good health, he says—if a 40-year-old person has a liver with a biological age of 40, does that automatically mean they’re healthy? We don’t have exact answers.
Regardless, Nwanaji-Enwerem thinks biological age is a useful metric for researchers because it gives them a quick, quantitative explanation for the myriad variables that affect the health of individuals and populations. If experts look at a community and notice that “people who live in this certain region all have accelerated aging,” he adds, they can then ask “is there a larger factor that we need to be looking at to help explain that?”
Can you control biological age?
If biological aging is a proxy to assess health and mortality, is there a way to slow it down? The strategies to prevent accelerated aging are pretty much the same ones we always hear about, La Croix says: balanced nutrition, adequate physical activity, clean air and water, low stress, strong social support systems, and access to healthcare—“all of those things that we associate with good health will be important.”
That said, experts don’t think regular individuals need to be thinking about biological age in everyday life. It’s not realistic for most people to test or measure, say, epigenetics on their own, and even if they could, it’s not like we have a pill or some other easy intervention to reverse it, Horvath says. There have been reports that specific diets and marathon training can knock years off an aging body, but in reality, we don’t have an anatomical time machine.
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La Croix points out that many of us already “think about [biological age] without even knowing that we think about it.” We notice how our bodies, cells, and abilities change over the years, and feel the effects of biological age even if we don’t use those words. Unfortunately, as the science stands, “you can’t turn yourself back into a 25-year-old,” La Croix says. But by keeping healthy habits and reducing risk factors, “all we can do is kind of optimize and enjoy life.”