In 2023, multimillionaire tech entrepreneur Bryan Johnson created a huge buzz when he revealed he’d devised a “blueprint” for reducing biological age and had made significant progress in rewinding the clock on his 45-year-old body. Not surprisingly, the internet — from news outlets like BBC to TikTok beauty and wellness influencers — lit up, with the topic continuing to create conversation. But what exactly is biological age, and can you actually reverse it?

We all know our chronological age, aka how many birthdays we’ve celebrated. But what if you’re 40, and your doctor says you have the physical conditioning of a 30-year-old? In that case, your doctor is referring to your biological age.

According to Jason De Leon, M.D., an emergency medicine physician with specialized training in bio-identical hormone replacement therapy (BHRT), biological aging (or senescence) is an intricate process marked by the steady decay of an organism’s vital functions. “As time passes, adaptability wanes, and vulnerability to stress, disease, and ultimately, death, surges,” he explains. “A medley of factors, including genetics, environment, and lifestyle, can mold the pace and consequences of aging.”

In lay terms, a number of biological and physiological development factors, including genetics and cellular turnover, can determine your biological age. For example, each strand of DNA is made up of chromosomes X or Y. At the tip of each point of the X (or Y) is a telomere. Scientists have discovered that telomeres get shorter with chronological age, and those with shorter telomeres are more likely to have chronic illness and early death. So, if you have shorter telomeres than someone with the same birth year as you, while you’re chronologically the same age, you’d be biologically older than them.

Why is any of this important? Research shows that adopting a healthy lifestyle lengthens telomeres, which then reduces the aging process — thereby decreasing biological age and potentially increasing the odds for a longer, healthier life.

So, biological aging is a real thing?

Yes. While chronological time signifies the time since birth, Dr. De Leon says biological aging delves deeper, reflecting an individual’s functional and physiological state in relation to their years.

“Accounting for a diverse range of factors, biological age encompasses genetics, lifestyle, and environmental influences, offering a more precise gauge of one’s health and aging trajectory,” he explains. “Thus, two individuals with identical chronological ages may exhibit divergent biological ages, shaped by variations in their genetic makeup, dietary choices, physical activity levels, and exposure to environmental stressors.”

De Leon says researchers rely on an array of biomarkers, such as telomere length, DNA methylation patterns, and blood-based indicators, to determine biological age. “A deeper comprehension of an individual’s biological age paves the way for tailored interventions to bolster health and, perhaps, decelerate the march of time.”

How do I find my biological age?

Determining your biological age isn’t an easy thing — after all, we aren’t all multimillionaire techies like Bryan Johnson. According to De Leon, it takes specific medical and blood tests governed by a medical professional, including determining telomere length and DNA methylation.

Elevated inflammatory markers like CRP, ESR, and cortisol in routine blood tests can suggest increased biological age, says De Leon, and higher baseline glucose levels and higher insulin levels are also associated with increased biological age “given the impact insulin resistance has on cells in the body.” Higher cholesterol levels are also associated with advanced biological age.

Additionally, De Leon explains that physiologic measurements, including muscle strength and cardiovascular fitness measurements like VO2 max, lung capacity, and cognitive function, all provide insight into one’s biological age.

And if you’re thinking of trying one of those online calculators or biological age tests, De Leon warns not to place too much weight on your results. “It may provide an estimate, but without actually evaluating telomere length or considering the pattern of DNA methylation, my impression is that these calculators may not provide an accurate age value,” he says.

Why does finding out my biological age matter?

If you can determine your biological age compared to your chronological age, you can make alterations to improve your lifestyle, says De Leon.

“Elevated biological age leads to age-related diseases like diabetes, heart disease, and neurodegenerative disorders,” he says. “Early detection proves an opportunity for timely intervention and additional preventative measures. It is distinctly possible that one’s indestructible perception of themselves is significantly misinformed.” In other words, you might think you have the healthy body of a 35-year-old woman, but in reality, your biological age might be closer to that of a 55-year-old body.

Most of us want more time — not less — with our family, friends, and kids. Learning more about biological age may give you the insight or encouragement you need to make changes that ensure you’re around longer for those people.

The good news is, unlike your chronological age, you can change your biological age, which will make blowing out those candles on the cake that much sweeter.