Biological Age vs. Chronological Age: Understanding the Key Differences

Most of us are familiar with the idea of aging being tied to the number of years we have lived, and that’s what we refer to as chronological age. It’s the traditional way of measuring how old or young we are. But there's another, perhaps more revealing, concept called biological age, which looks at the state of our body on a cellular level.

If someone asks how old we are, we tend to instinctively respond with our chronological age. But that number may not always tell the full story; two people of the same chronological age could very well live entirely different biological realities. One might have the internal health of someone much younger, while the other’s body could already be showing signs of premature aging.

Though biological age is still a developing concept in science, it offers a new lens through which we can view aging. And by looking at how both perspectives intersect, we move one step closer to understanding the aging process — a phenomenon that, to this day, holds many unanswered questions.

What is biological age?

Biological age refers to how our body ages on a cellular and molecular level — internally, so to speak. The term first emerged in 1988 as researchers sought to better understand age-related changes in the body.

The concept of biological age challenges the notion that chronological age is the best predictor of a person’s physiological state. See, while chronological age simply refers to the time from birth to the present day, biological age takes into account specific biomarkers and several other factors that aim to reflect how the body is functioning.

And so this leads to the theory that biological age might provide a more accurate indication of a person’s true age and overall health. Research today suggests that biological age may, in fact, become a more reliable indicator of age than the conventional chronological measure.

But while it has been decades since the concept of biological age first came about, practical difficulties in estimating biological age still persist. Identifying the most reliable biomarkers and standardizing methods remain significant hurdles, making this field still very much a work in progress.

The aging process: chronological vs. biological age

Aging as a term can be defined as a time-dependent functional decline of an organism at all levels, from nanoscopic (extremely small, at the molecular level) to the whole person. But aging as a process is inherently complex — one that, when viewed through the lens of either chronological age or biological age, can be interpreted quite differently. As I mentioned earlier, there are still many unknowns when it comes to the aging process, with much of it remaining unexplained.

Much of what we now know about aging we draw from biological processes called hallmarks of aging. There are 12 identified hallmarks, some of which include cellular senescence, chronic inflammation, epigenetic changes, and mitochondrial dysfunction.

These hallmarks do point to the root causes of aging, but most of our understanding of them today still comes from animal studies. And because human biology is far more complex, applying these findings directly is not always feasible.

We do, however — and when I say 'we,' I’m referring to the scientific community — attempt to measure these processes in laboratories and pinpoint the biomarkers associated with them. These biomarkers are then used to find correlations between them and either a person’s chronological age or the state of health that typically corresponds to that age.

Reflecting on what we just discussed here, it becomes clear that while chronological age simply marks the time passed since birth, biological age is the concept that can capture physiological deterioration, or aging, better. The challenge, however, is still with finding the most reliable biomarkers.

Now, if, and perhaps once, these biomarkers are fully understood and validated, they could help us evaluate aging interventions more effectively and make more accurate predictions about age-related diseases and conditions, including the ultimate measure of biological and functional decline — mortality.

Side-by-side comparison of chronological and biological age

Now let's have a look at chronological and biological age side by side to better understand their differences and how each serves as a measure of aging.

Measuring biological age

The process of accurately measuring biological age is fundamentally intricate but know that there is no single test or method that would say, “Your biological age is X.” Instead, to measure and predict biological age, researchers run a combination of tests. Let's now take a closer look at some of these tests and methods.

Lifestyle factors that influence biological age

If I were to suggest that our appearance is a good reflection of our age, most people would probably nod in agreement. How we look and age over time is, of course, largely determined by our genes, but it is also determined by lifestyle factors. For example, think of someone who's smoked for years versus one who has not smoked but instead done a relatively good job of taking care of their body — it's likely we could easily tell which one appears younger. And indeed, scientific research supports this idea, showing that people who maintain a healthy lifestyle tend to experience slower biological aging.

A recent review article found that people with healthier lifestyles may experience slower biological aging because their DNA methylation profiles and physiological biomarkers are better than those who don’t live as healthily. An earlier study from 2013 explored how behavioral and lifestyle factors influence the rate of biological aging. It observed that factors such as diet and physical activity significantly impact the rate of biological aging.

So, generally, when we talk about lifestyle factors, the ones that could influence biological age include the following:

• Diet and nutrition
• Physical activity and exercise
• Smoking status and alcohol consumption

But while studies do link lifestyle factors to biological age, I should still point out that most such studies are cross-sectional in design. This means they only provide a snapshot of data at one point in time, which is not sufficient to say for sure if these factors actually cause changes in biological aging or if they are simply associated with it. To truly establish cause and effect, we simply need more longitudinal research material.

The impact of lifestyle on the aging process

Aging is something we all experience, and it’s an inevitable part of being human. But as we grow older, the impact of our lifestyle choices becomes more apparent. Our bodies undergo changes, from physical appearance to muscle and cognitive function. Wrinkles and age spots may appear, our hair may turn gray, and we may even lose a bit of height. Muscle and bone mass naturally decline with age, and memory can fade, making it harder to process information or recall memories.

But while these changes might seem like 'just a matter of time,' our lifestyle does play a significant role in either speeding up or slowing down this aging process. Here’s what science tells us about how our habits influence aging.

A study called The Million Veteran Program, conducted by researchers in the United States, examined data from questionnaires and medical records of 276,132 veterans between 2011 and 2019. It identified eight lifestyle habits that are associated with a lower risk of early death and increased life expectancy.

1. No smoking
2. Physical activity
3. No excessive alcohol consumption
4. No opioid use disorder
5. Managing stress
6. Having positive social connections
7. Eating a balanced diet
8. Getting good quality sleep

But what I would say is particularly interesting about these lifestyle factors is that they aren’t some ahead-of-our-time-type discoveries. In fact, most of us already know that things like eating well, staying active, and managing stress are good for our health and contribute to longevity. We don’t necessarily need science to tell us that — it just makes sense.

The hard part, though, I would say, is staying consistent. Building these habits into our daily routine and avoiding harmful ones isn’t about one-time efforts; it’s more about sticking with them over the long run.

I have personally experienced this with exercise, something I have done for most of my life. There’s this idea that’s floating around that if you push yourself hard during one workout, you can somehow make up for weeks of poor eating or inactivity. But the truth is, no matter how intense that one session is, it won’t erase the damage done by weeks of processed food or excessive calories. You would need just as much consistency to balance out the negative.

And that’s really the key to longevity: small, positive choices repeated consistently over time. One great workout won’t undo weeks of bad habits, just like one year of healthy living won’t erase a lifetime of neglect. But with patience and commitment, these daily efforts, I believe, can really help us age more gracefully and, in a way, buy ourselves more time.

Can you reduce your biological age?

Reducing biological age is something that would likely interest most. However, as of today, there's no solid scientific evidence proving that lowering biological age metrics directly impacts health outcomes. Yet, this hasn’t stopped the idea from becoming a popular trend.

In fact, we are now seeing longevity leaderboards and so-called "Rejuvenation Olympics," where the most devoted biohackers and longevity enthusiasts compete to see who can slow down their biological aging the most. And while this practice has no firm backing of science just yet, it may not be as far-fetched as it seems. After all, such competitions, especially healthy competition, can actually inspire people to make positive lifestyle changes — which, in the long run, could very well prove beneficial for healthy aging. Also, with the pace at which science is evolving, we might be closer to meaningful discoveries than we think.

Bottom line

Considering everything we have discussed, it’s evident that biological and chronological age are entirely different concepts for measuring aging. Chronological age is always fixed and reflects the time since birth, while biological age captures how our body ages on a cellular and molecular level and aims to give a more accurate reflection of our true health status.

However, there is still a great deal left to learn about aging as the intricate process that it is, and advancing our understanding is absolutely key to developing future interventions that could help more accurately calculate biological aging — and perhaps even slow it down.