Your Biological Age
You've probably stood at this fence before: You're chatting with someone who's approximately your age, but one of you seems much older than the other one.
This mildly awkward scenario illustrates the difference between chronological and biological age. Tomorrow each one of us will be exactly one day older, but our bodies are aging at different rates, biologically speaking.
This newsletter was prompted by an NPR Morning Edition report earlier this week entitled "You can order a test to find out your biological age. Is it worth it?" I want to address four questions:
1. What is biological age?
2. Should you order a test to find out your biological age?
3. Can you influence the rate at which you age?
4. How accurate are recent news reports on biological aging?
I'll also be saying a few words about flaws in statistical reasoning that routinely crop up in discussions of health data.
1. What is biological age?
Aging can be thought of as physical deterioration that accumulates over time. Biological age refers to how much deterioration has accumulated.
That's an intentionally vague definition, because scientists don't agree yet on the specifics. (I'll share some examples in a moment.)
A useful characteristic of biological age is that it's more accurate than chronological age at predicting outcomes such as how long people live.
For instance, over time, parts of your DNA acquire hydrocarbons known as methyls. Methyls don't alter your DNA, but they do change the way genes function, and some of those changes affect your health.
Methylation in specific DNA sites turns out to be a better predictor than current age of how much longer people will live.
I find that pretty amazing. If a biologist wanted to predict the life expectancies of a large group of people, she wouldn't need to know the peoples' ages. Just by analyzing tiny samples of saliva or blood, she could make more accurate predictions overall.
At the same time, methylation is malleable. Each person's lifestyle can positively or negatively impact the process – and thus health and life expectancy. This is one reason the biologist's predictions wouldn't be perfectly accurate.
(Is this newsletter going to turn into one of those slightly annoying calls for a healthier lifestyle? Well, yes. But there are also some reassurances if you're not a teetotaling vegan whose idea of a wild evening is swapping out yoga for a spin class.)
Another useful characteristic of biological age is that it can be calculated for specific organs and tissues, and the values for any one person might not turn out to be the same.
Saying that my liver might be older than my bone marrow sounds odd, but only when you think of aging in terms of calendar time. It's not so odd when you think of it as accumulated damage at the cellular level.
Measuring biological age
Biological age is measured in dozens of ways. Measurements that include DNA methylation are widely considered to be most accurate, and are referred to as epigenetic clocks.
"Epigenetics" refers in part to environmental influences on gene expression that don't alter the underlying DNA sequence. A simple example woud be some of the differences in appearance that emerge among identical twins, in spite of their shared DNA.
What does it mean to say that epigenetic clocks are the "most accurate" approach to measuring biological age? In what sense are they accurate?
One meaning of this statement is that epigenetic clock values outperform other measures at predicting later health and life expectancy.
These values are not expressed as years, but rather in technical terms (e.g., patterns of methylation). To better understand this, I reached out this to Dr. Jesse Poganik at Harvard Medical School. Among other things, Dr. Poganik is one of the principal authors of a 2023 framework for the identification and evaluation of epigenetic clocks and the many other biomarkers of aging.
As Dr. Poganik noted in his email to me, "aging biomarker values are often transformed to correspond to chronological ages of a reference population, as this is a readily understandable way of conceptualizing [biological] age."
This makes sense. It would be more understandable to learn that your biological age is 28 than to be presented with technical details about your methylation.
Although different biomarkers are transformed to chronological ages in different ways, Dr. Poganik pointed out that the transformation is often done to match the chronological age of the average person who has the same biomarker values.
In other words, people whose biological age is 34 have DNA methylation levels (or some other biomarker values) of the average 34-year-old.
This way of using averages raises some statistical issues that I'll tease out in the next section.
2. Should you order a test to find out your biological age?
If you're willing to spend anywhere from $100 to $500, you can find out your biological age. Just mail one of the dozens of companies a small sample of blood, or saliva, or stool (or all three), and within a few weeks you'll receive personalized results.
There's a lot of variety in the results you might get. Some companies offer a single age. Some tell you how rapidly you're aging, a separate but less well-established kind of measure.
I mentioned earlier that different regions of the body age at diferent rates. Indeed, some companies will provide this kind of disaggregation. Elysium Health, for instance, tells you the biological age of nine "systems", including your immune system, metabolism, heart, and brain.
Some companies seem credible and are supported by leading scientists. The institutional affiliations of the scientists are mentioned on the websites.
Other companies try a little too hard to simplify the technical material, and the credibility of their in-house experts seems questionable.
For instance, the Purovitalis website says that seeing your biological age "is like finding out how young or old your body feels and acts". I find this statement confusing. Maybe I'm just cranky, but my body isn't something separate from me that leads its own emotional and behavioral life. I don't need a test to tell me how my body feels.
Also, the only scientists on the Purovitalis team seem to be a pharmacist and a "biochemist & formulation specialist". They're identified on the Purovitalis website by their first names only, which is a friendly touch, but nothing is mentioned about their backgrounds or expertise.
Inevitably, most of these companies not only sell biological age reports, but also supplements, consultations, and other resources that will allegedly help you slow or reverse the aging process. The fact that they do so doesn't mean their tests are invalid, but it is a reminder to be cautious.
So, should you spend your money on one of these tests?
A compliment sandwich
The so-called compliment sandwich is the notion that when criticizing someone, you should start by praising them, then offer criticism, and then close with additional praise.
I will attempt one of these sandwiches here, but I can tell you in advance: the bread is pretty thin.
As some researchers have pointed out, knowing your biological age, expressed in years, could be useful. For instance, if it's much higher than your chronological age, you should consider seeking medical attention.
Still, you might question the value of paying for an estimate of your biological age when a routine physical exam might provide roughly comparable information. For example:
—If a doctor says your blood pressure is high, you should be concerned because of known associations between high blood pressure at your age and cardiovascular disease later in life. This is aggregate data though; it doesn't yield much certainty about outcomes for one particular person (i.e., you).
—If the biological age of your heart is greater than your chronological age, you should be concerned, because the risk of cardiovascular disease increases with age, and you already have an "older" heart. This is also aggregate data, and doesn't yield much certainty about outcomes for you.
So, why not just go the doctor and get more information of relevance to your cardiovascular health (blood pressure, lipid levels, etc.)?
Main concerns
So far I've only suggested that knowing your biological age doesn't benefit you much more than a physical exam, even if biological ages are easier to understand than all that data in your patient portal.
Here are the three main reasons why I wouldn't recommend spending money on finding out your biological age:
(a) Validation issues.
Research on epigenetic clocks and other measures of biological age is still relatively new, and so the validity of these measures hasn't been fully established. Here's how Dr. Poganik put it:
"My opinion is that any claim of individual-level biological age predictions should be taken with a grain of salt at this point in time. Many companies are selling the tests to the public, but the reason these measures are not yet widely used in clinical trials is that they have not been systematically validated."
(b) Generalizability issues.
Once again, Dr. Poganik:
"We need more rigorous validation of biological age biomarkers across populations so that we can be confident that the measures are broadly applicable beyond the population/group in which they were developed."
In other words, more extensive study is needed to determine population values for each biomarker. We need to study more 34-year-olds, for instance, to understand what the average DNA methylation levels are for people that age.
I reached out separately to Dr. Brian Chen, an expert at UCSD. His assessment was comparable, and he added the following:
"The other key aspect that is often overlooked is the level of “technical reproducibility” (ie, if you ran the same sample multiple times, how wide is the spread of results) each model has."
In other words, if you just take one sample of North American, female-at-birth, generally healthy individuals, and you calculate the DNA methylation levels (or whatever) for the average 34-year-old in this group, you still won't know the true average, because a different sample is likely to yield different values. More sampling is needed to better estimate the average and the extent of variability around it.
(c) Ecological fallacy issues.
The "ecological fallacy" refers to unwarranted inferences about individuals based on group data.
If your biological age is 34, it's not clear that you'll have the same health outcomes and life expectancy as the average 34-year-old, because there hasn't been enough longitudinal research yet on individual changes in biological age and its health impacts to make clear predictions about what will happen to you, the individual. Over time your health may or may not change in the way that the 34-year-old's does.
Dr. Poganik attributes the dearth of longitudinal studies to the cost of biomarker measurements, while noting one prominent exception, the Dunedin Study, that has been tracking a cohort of roughly a thousand New Zealanders since birth.
Though I'm hinting here that a biological age report would be a waste of money, you might still be tempted to get one. (I have to admit it sounds intriguing.) If do you want to proceed, I suggest avoiding the "best biological age test" web pages, because they appear to be sponsored in part by the companies they review. Instead, look at individual websites and choose a company that mentions close collaboration with at least one academic expert. You're still buying a product, and it might still be snake oil, but this may help steer you toward the best option.
The final part of the criticism sandwich is this: The research is new, and in spite of the many financial incentives, it's mostly good science rather than "you can live forever" fluff. Biological age research has forensic applications (e.g, identifying approximate age based on DNA samples) as well as the potential to help slow or perhaps even partially reverse the aging process. This brings me to my next topic, and the best news of the day.
3. Can you influence the rate at which you age?
Scientists may not agree on the best definition of biological age, and the data may not yield accurate predictions for any particular individual, but biological age is malleable. We can speed up or slow down the rate of aging.
In a sense, there's nothing remarkable about saying this, because researchers intentionally choose measures of biological age that respond to environmental influence.
Still, I don't recommend emulating Bryan Johnson, the tech entrepreneur who claims to spend more than $2 million per year on staying young – and, unsurprisingly, monetizes his efforts via supplements and other resources you can purchase on his website. For one thing, an L.A. Times reporter who covered Mr. Johnson's latest "Don't Die" hike noted this week that he doesn't even look that much younger than his age. (He's 46; see below.)
At the same time, I do see biomarker-related evidence supporting conventional strategies for promoting health. All of the suggestions below, other than the last two, have been linked to more favorable epigenetic clock readings:
—Eat well. As Michael Polllan put it, "Eat food. Not too much. Mostly plants." This is great advice, although if you're more or less vegetarian or vegan, you need to choose your plants carefully to get enough protein, Vitamin B-12, and Omega-3 fatty acids. For more information, see here.
—Exercise regularly. Also great advice, if tweaked appropriately (engaging in micro-exercise or breaks if you sit for long periods; making age-related adjustments; etc). See here and here for additional details.
--Manage your stress. Easier said than done, but worth pursuing because roughly 70 years of research shows that stress is a direct contributor to many physical and mental problems. (For resources, see here.)
—Sleep well. Also easier said than done. See here for suggestions.
—Don't smoke. Smoking strongly influences biomarkers of aging, and similar findings are now emerging for vaping. (Anti-vaping ads should say that vaping makes you old. Isn't that the scariest thing you could tell a teenager?) Support for quitting can be found here.
—Drink minimally. As I've discussed in prior newsletters, it's not clear from the data exactly what "minimally" would mean, but if you drink every day, more or less, you might consider reflecting on how much you consume at a sitting. See here for further recommendations.
—Avoid environmental threats. This is a grab-bag of suggestions ranging from using sunscreen, to throwing out your Trader Joe's frozen rice pilaf (the USDA warned today that it contains rocks), to skipping the latest Tik Tok challenge. I have no idea what the latest challenge is, but I assume I'll read about it when someone gets hurt.
—Get an annual physical. In other words, get a physical exam, not a report on your biological age.
4. Are news reports on biological aging accurate?
Yes and no.
There's been a low but audible buzz in news and social media about biological age. Along with the NPR report this Monday, there have been articles in the past couple of months in the New York Times, the L.A. Times, The Conversation, and so on.
The best of these articles clearly describe biological aging, emphasize that the science isn't settled yet, and recommend caution about shelling out hundreds of dollars to learn your biological age.
What's missing is a concrete sense of what biological age, expressed in years, would mean.
Imagine receiving a report that you're 34, biologically speaking. The NPR piece and other reports don't make it clear that in some cases, this means that with respect to some epigenetic clock you're like the average 34-year-old, while in other cases, you won't know what it means.
As I discussed earlier, being like the average 34-year-old according to an epigenetic clock doesn't necessarily tell you much, because it's unclear whether you in particular will continue to age in the way that this 34-year-old would.
I can understand that journalists want to be cautious about dissing products grounded in an emerging science. I don't have to be. Commercial reports on biological age seem like a waste of money at the present time. Meanwhile, research on biological age is flourishing and promises to contribute to our leading longer, healthier lives.
Thanks for reading!