This article is from The Checkup, MIT Technology Review's weekly biotech newsletter. To receive it in your inbox every Thursday, sign up here.

It’s spring here in the Northern Hemisphere. There are daffodils, tulips, and hyacinths in full bloom in parks and window boxes where I live in London. I even saw some lambs on the weekend. But here I am, thinking about how close I am to death.

Last year, I took a test to find out my biological age. These tests, which involve assessing chemical markers on your DNA, aim to estimate how much wear and tear you’ve experienced so far—and, essentially, how many years of life are left in you.

I was 35 when I took the test. And my results suggested that my biological age was 35 too. That indicates I’m aging at a normal rate compared with other people we have data for. But the company that ran the test has updated its offering since then. A couple of months ago, it reanalyzed my results to give me an individual biological age for each of nine systems, including my brain, liver, heart, and blood.

I was disappointed when I learned last year that despite a plant-based diet and regular yoga, I am no more biologically youthful than average. So imagine how upsetting it was to learn that the biological age of my brain is four years above my chronological age. My liver is a shocking seven years older. Yes, I’m British, but I don’t think I drink that much. How much should we read into results like this?

The first aging clocks, developed around a decade ago, were designed to analyze epigenetic markers on DNA from saliva samples. These markers are essentially chemicals that attach to our DNA and control how our genes make proteins. Research has shown that the patterns of these markers align with age. Scientists can train algorithms to estimate a person’s age just by analyzing them.

Since then, scientists have improved on the technology. New clocks incorporate not only your epigenetic markers but a range of other health biomarkers, such as blood sugar levels and white blood cell count. These tests may give us some idea of a person’s biological age—not just how many birthdays have passed, but how many years of healthy life might lie ahead.

Today, there are plenty of aging clocks out there. Some have been developed for specific organs, and others have been designed for particular animal species. Some analyze blood samples, and others assess the microbiome. The test I took last year, developed by the company Elysium, uses saliva samples and assesses epigenetic markers.

The team at Elysium has since expanded the remit of the test. Send off a miniature tube of saliva, and you’ll soon be told not only your overall biological age, but the specific biological ages of your heart, brain, liver, kidneys, and blood; your metabolic, immune, and hormonal systems; and what they call your inflammation system.

These scores were developed by assessing how various biomarkers associate with the health of those individual systems, says Lenny Guarente, chief scientist and founder of Elysium and the Novartis Professor of Biology at MIT. (MIT Technology Review is funded by the university but remains editorially independent.) Scientists at the company have incorporated health and mortality data from large studies of volunteers (although they won’t say how many). These studies have thrown up biomarkers that indicate the health of individual organs. By linking these to patterns in the epigenetic markers on DNA samples, the company’s proprietary algorithms can estimate biological ages for each system.

Elysium’s analysis of my saliva, which I sent them last year, revealed that even though my biological age matched my chronological age at the time, the ages of my individual systems are all over the place.

My brain was given a biological age of 39, and my liver 42. My hormonal system isn’t looking great either, with an age of 41. On the other hand, my kidneys and inflammation and blood systems are all estimated to have a biological age of 34—slightly below my chronological age. And my heart is faring best of all, with a biological age of 31. Yes, I am officially young at heart.

Presented with these results, I found it difficult to stop my mind from going into overdrive trying to interpret them. My brain must be old because I’m stressed and I don’t get enough sleep. Maybe I drink too much, or I’ve taken too many painkillers over the years, and my liver has struggled to keep up. I have endometriosis—could that have affected the way my body makes and responds to hormones? The young heart comes as a surprise, given that heart problems run in my family. But I’ll take it.

The next step is working out what to do with these results. Elysium offers a set of recommendations for each of your scores. For my old brain, the company recommends I get more exercise, socialize more, get enough sleep, and avoid smoking and alcohol. It also recommends I take the supplements the company sells on its website.

The thing is, I already know I should be getting more sleep and exercise. I’d wager pretty much all of us know this. Is a biological age score going to change our behavior? It won’t for me—if I had the time to exercise and sleep more, I’d be doing it already. I asked Elysium’s vice president of bioinformatics, Dayle Sampson, if knowing his own scores changed anything for him. It hasn’t.

Sampson tells me he’s 38 years old, and according to Elysium’s test, his biological age is 36. But his brain age came out at 43. He thinks he gets too much exercise, which has been linked to an accelerated rate of aging in some studies. Has he cut down since he got his test results? “No,” he tells me.

At any rate, we don’t know how accurate tests like these are. The people at Elysium are the first to admit that their test doesn’t incorporate many factors known to influence how we age. It doesn’t consider the role of the microbiome, for example. Or a process called senescence, in which aged cells generate a toxic brew of inflammatory chemicals that can damage the surrounding tissue.

And it’s difficult to evaluate how the test works, because the company won’t give much away. It won’t tell me which biomarkers the research team considered, how these biomarkers are associated with wear and tear in any particular organ, and how they align with epigenetic markers that can be measured in a saliva sample.

When it comes to assessing how old a person’s brain is, it’s very unlikely that a test based on epigenetic markers is going to give you the full picture, says Paul Shiels, who is researching biological clocks at the University of Glasgow in Scotland. “I would have thought you would want to know about performance,” he says. Scientists have developed plenty of tests for cognition, memory, and intelligence, for example. None of these have been incorporated into my brain age score.

We could say the same of the other organs too, says Shiels, who is researching how well kidneys age. “You cannot clinically use a saliva sample to give you any [information about] the functional capability of your kidney,” he says. Blood and urine tests are required to assess how well a person’s kidney is working.

That’s not to dismiss the work being done by researchers at Elysium and elsewhere. The science here is fascinating, and it’s still new. The team at Elysium says its test is the first of its kind, and a work in progress. “These clocks should not be viewed as fixed,” says Guarente. “These are things we want to continue to improve … we think that they will evolve and get better.”

Read more from Tech Review's archive

In case you missed it, here’s my piece from last year about my biological age score, and what we can make of these tests and their results.

Every year, Tech Review publishes a list of 10 Breakthrough Technologies. Last year, our readers picked aging clocks as an 11th breakthrough. I wrote about how far the technology has come.

Many people developing aging clocks hope to be able to use them to test whether life-extending treatments work. Research into longevity is getting huge investment from the uber-wealthy. I wrote about my wild experience at a conference for billionaire investors who want to live for longer.

My colleague Antonio Regalado has reported that Sam Altman, CEO of OpenAI, has invested $180 million in a company trying to delay death. Antonio has also reported on Saudi Arabia’s plans to invest a billion dollars into longevity research.

Longevity research goes beyond people. Meet the scientists trying to extend the lifespans of pet dogs. And, eventually, their owners.

From around the web

Men who support gender equity are more likely to be willing to try male contraceptives, whenever they finally become available. (Contraception)

Last week, Judge Matthew Kacsmaryk of the US District Court for the Northern District of Texas invalidated the Food and Drug Administration’s approval of the abortion pill mifepristone. His ruling was filled with language used by anti-abortion groups and statements that fly in the face of scientific evidence. (New York Times)

Michael J. Fox was awarded an Oscar last year. But his real trophy was a breakthrough in the understanding of Parkinson’s disease. Fox’s foundation has pumped hundreds of millions of dollars into a study that has been running since 2010, which provided strong evidence that the presence of a particular misfolded protein might help diagnose Parkinson’s disease and could aid the search for a cure. (STAT)

The longest-lived among us might have their microbiomes to thank. Centenarians have a gut microbiome typically associated with younger people. (Nature)

How often should you get a covid booster? The official guidance varies by country. Here’s what the science says. (Scientific American)

Update 4/19/23: This story has been updated with Guarente's MIT affiliation.