Aging & Longevity

Can Aging be Reversed? Expert Thinks Not

American biologist and expert on aging Matt Kaeberlein is skeptical of turning an elderly animal into a youthful one with double the lifespan.

By Noemi Canditi

Key Points:

  • Though there is no shortage of methods for gauging biological age, does a decline in any of these metrics suggest a slowing of the aging process?
  • Expert Dr. Matt Kaeberlein explains why he thinks that no research has shown a way to reverse aging—yet.

In the field of aging research, Matt Kaeberlein has earned a solid reputation as a scientist. People pay attention when Dr. Kaeberlein speaks publicly about aging.

So, when Dr. Kaeberlein tweeted that he pushes back on the concept of “reversing aging” and then goes on to joust with some of his esteemed contemporaries, it’s safe to say he’s not doing so just for the eyeballs—he wants to set the scientific record straight and temper expectations.

To find out if scientists can currently reverse aging, let us examine the person who tweeted this, what he said, and the responses he collected.

Who is Matt Kaeberlein?

Through his research on the aging process, Dr. Kaeberlein hopes to discover methods that will not only help people live longer and healthier lives, but will also make them happier and healthier in general.

He has written more than 200 academic articles and is the director of the Healthy Aging and Longevity Research Institute at the University of Washington. Dr. Kaeberlein has collected a plethora of honors and is a fellow and board member of numerous esteemed scientific organizations.

Dr. Kaeberlein has been in the spotlight recently for a number of reasons, but perhaps most notably for his work as co-Director and founder of the Dog Aging Project, one of the largest studies in the area of aging research. He is leading a clinical trial to determine whether the drug rapamycin, which increases longevity in rats, has the same effect on dogs, and has argued publicly and in scientific articles that clinical trials in humans are warranted.

Kaeberlein’s original tweet via X

What did Matt Kaeberlein say?

At the heart of Dr. Kaeberlein’s tweet is how to define “reversing aging.”

“Improving health is not reversing aging.”

When people talk about aging, they bring up two key concepts: “lifespan” and “healthspan.” We’re all pretty familiar with the idea of lifespan, which is the length of time for which a person or animal lives or a thing functions. Healthspan is actually something we’re probably all conceptually quite familiar with; it has to do with the number of years spent in good health compared to those spent sick.

So, what Kaeberlin may be saying here is that making someone live longer or live a life with more years in good health is not the same thing as reversing aging.

“Reversing one or a handful of age-related phenotypes is not reversing aging. I can do that with exercise, a healthy diet, or hair coloring.

When Dr. Kaeberlein says “age-related phenotypes,” he may be referring to a few things.

He seems to be pointing to things that any non-scientist would likely associate with aging, such as the graying and whitening of hair, the sagging of skin, and the weakening of our muscles and bones.

But he also seems to be referring to several characteristics or metrics for biological aging—the gradual deterioration of a living organism’s functional characteristics. Although he doesn’t directly mention it, Dr. Kaeberlein may be pointing to what some scientists call the “hallmarks of aging”—a handful of measurable things that happen within cells and tissues that are linked to or have been shown to cause aging. Some examples of aging hallmarks are the shortening of protective ends of chromosomes called telomeres and the transformation of cells into a “zombie-like” state called senescence.

So, Dr. Kaeberlein’s definition of reversing aging doesn’t have to do with living longer, healthier, or aging slower. His definition stays true to the term “reversing,” or moving backwards.

“If anyone can show that they have made an old animal into a young animal and it goes on to live twice as long as it would have, I will agree you have reversed aging and be your biggest fan.”

If anything, Dr. Kaeberlein has spent his career on the hunt for a way to reverse aging, he just doesn’t think that he or anyone else has ever shown true aging reversal.

“In fact, as far as I know, yet another year has passed and nobody has published any peer-reviewed data showing they can even match the absolute effects of rapamycin or caloric restriction on lifespan and healthspan metrics in lab animals. I would really like to be proven wrong, but until we get some hard data, I’ll keep saying that it’s dishonest to claim you’ve ‘reversed aging.’”

He just doesn’t think that anyone has actually shown that this is possible…yet.

A response from David Sinclair on X

David Sinclair

When people mention aging scientists, there may be someone who comes to mind just as readily as Dr. Kaeberlein, and that’s Dr. Sinclair (who has 434.2K X followers to Kaeberlein’s 21.8K).

He’s published a best-selling novel on aging and longevity called Lifespan and has been on major national TV networks talking about his daily regimen of vitamins and supplements that he believes will make him live longer.

He also has been a major backer of resveratrol, a molecule found in red wine (among other consumables) that he claimed reversed aging. Dr. Sinclair also used to say he drank a glass of whiskey every day and how this was essential to his anti-aging routine, only to reverse course on it not long ago. In an interview a few months ago with GQ, Dr. Sinclair said that it turns out that any amount of alcohol is bad for you and that even one glass of wine can hold you back.

Love him or hate him, Dr. Sinclair is a major voice in the field of aging, and he’s changed his direction in research as of late from what some may have thought of as gimmicky to something that’s a bit more biotechnologically driven. Dr. Sinclair has been working on a system called OSK, which stands for 3 genes that have been shown to be able to reprogram mature cells back to stem cells, testing whether applying this system to a whole organism can have a Benjamin Button effect.

In his reply, Dr. Sinclair points out the latest research from his lab:

Here, we show inducible OSK system in 124-week-old mice extends the median remaining lifespan by 109% and enhances several health parameters.

Without going too into the technical details here, the first thing to point out is that Dr. Sinclair basically disregards what was at the heart of Dr. Kaeberlein’s argument: that increasing lifespan and improving health has nothing to do with reversing aging. Not only that, this isn’t peer-reviewed, published research.

For all intents and purposes, Dr. Sinclair’s comment appears to lean more on the side of self-promotion than thoughtful scientific dialogue.

A tweet from Karl Pfleger on X

Karl Pfleger

Dr. Pfleger is one of the more prolific angel investors in the longevity industry (naturally, he is an investor in Repair Biotechnologies, a gene therapy approach to the reversal of atherosclerosis).

What stands out most among some of the interesting comments in Dr. Pfleger’s tweet response to Dr. Kaeberlein is the idea of repeated dosing:

Part of the litmus test should be ability to re-apply the treatment repeatedly, every so-many years (humans) or months (rodents) to repeatedly demonstrate reversal of many of the slowing accumulating biomolecular changes of aging.

He also invokes Dr. Aubrey de Gray’s hypothesis for “damage repair 1.0,” which argues that reversing aging should focus on rationally-designed damage repair approaches that are predictable. This brings us back to the idea of the hallmarks of aging—if they truly are hallmarks of aging, then if they are reversed, then an organism should become younger and live longer.

The random armchair scientist

There were many responses from self-proclaimed “longevity maximists” and “transhumanists,” none of which were able to show Dr. Kaeberlein a paper that he had not already seen.

Of note, several of the papers brought forth deal with a measurement for biological aging called “epigenetic age”—a score that estimates a person’s aging based on patterns of modifications that decorate our DNA that have been previously found to be associated with mortality, physical functioning, and cognitive status in addition to other markers of health. There isn’t one official epigenetic age test, and while researchers are constantly trying to improve upon the concept, more and more companies are being rolled out offering epigenetic aging tests.

Nevertheless, there’s no new or hidden gems of research when it comes to epigenetic aging (although there are some great X/Twitter battles among aging scientists about it) that are going to make Dr. Kaeberlein eat his words.

The Verdict?

Dr. Kaeberlein’s comments on aging reversal seem to be pretty sound. That being said, Dr. Kaeberlein doesn’t seem to intend for his comments to discourage anyone from pursuing aging reversal. After all, his tweet ends with the following:

I would really like to be proven wrong, but until we get some hard data, I’ll keep saying that it’s dishonest to claim you’ve “reversed aging”.

To The Top