Antiaging enthusiasts are getting $16,500 injections to make their knees young again

• Stem-cell therapy, though costly and unregulated in the US, shows promise for age-related diseases.
• The wealthy are flying to Aspen and the Bahamas for stem-cell injections in their joints.
• CEO Bryan Johnson spends $2 million a year on his body and claims he now has "superhero joints."

It's hard to outrun aging if even a short walk makes your knees hurt.

Sure, you can tweak your diet, your workout, and even get Botox. But offsetting the wear-and-tear on our joints is not so simple.

Take the tech entrepreneur Bryan Johnson, who — despite spending $2 million a year to feel 18 again — has struggled to find a fix for his achy, 46-year-old knees and hips.

He claims he finally has a solution: flying to the Bahamas for an experimental therapy to have millions of stem cells from young, healthy Swedish volunteers injected into his knees, hips, and shoulders. The price tag? About $16,500 per joint, or a whole-body combo for $25,000.

This is not new science; stem-cell-therapy research has already shown promise as a potential treatment for aging-related ailments such as diabetes, heart disease, and arthritis . But using it to limber up the knees of healthy (and wealthy) 40-somethings is new territory.

And Johnson isn't the only one taking advantage of this trend.

The wellness industry is buzzing with furtive excitement about the idea of rejuvenating knees with a shot of young cells.

While not FDA-approved in the US, some clinics abroad are able to provide the treatments with the approval of regulatory agencies in other countries — for a price. A massive market of unregulated clinics are already cashing in on consumer interest in the therapeutic power of stem cells to the tune of $1,200 to $28,000 per treatment, research has found.

Leaders in the longevity field say this is a promising idea, and experiments like Johnson's may even help to nudge the healthcare paradigm toward proactive, preventive care for our joints.

For now, here's what we know — and what we don't know — about stem-cell therapy for knees.

A shot to supercharge the body's natural healing ability

In Johnson's pursuit of "superhero joints," he flew to Physical Longevity, the Bahamian clinic that is developing experimental antiaging treatments, largely with stem cells.

He didn't want just any stem cells. Johnson booked a specific type of treatment involving mesenchymal stem cells, or MSCs. These cells are all the rage in longevity circles these days because they seem to reduce inflammation and promote regeneration. Research suggests that, unlike other cells, they can act alone — isolated from other tissues, naturally gravitating toward injured or dysfunctional tissues to help repair them.

Speaking to BI about a month after his procedure, Johnson said he hasn't noticed much change yet.

"That's probably because my health biomarkers are already in the top 1% as far as muscle, fat, metabolic health, cardiovascular health, et cetera," Johnson said, citing the health stats he shares on his website . "So it's pretty difficult for my subjective feeling of wellness to improve."

Still, Johnson said he's waiting for the objective data to see the benefits, trusting a process he developed over years (with millions of dollars) to determine which longevity treatments are worth it. He hired a team of medical experts who evaluate peer-reviewed studies on potential longevity treatments, ranking the quality of evidence, Johnson told BI. MSC therapy made the cut as a treatment of interest, and Johnson said he and his team felt the clinic and stem-cell provider were trustworthy and safe.

Currently, the only FDA-approved stem-cell therapies available in the US use the patient's own cells. While that's effective for some things, it may not do very much to rejuvenate your joints, Rasul Chaudhry, a professor of biological sciences at Oakland University who specializes in stem-cell research, told BI. It's tough to reverse age-related damage with cells that have aged with you, Chaudhry pointed out.

Younger cells drawn from healthy volunteers seem to be better at repairing and regenerating damage — at least that's what Johnson's doctor, Steven Sampson, told BI. Chaundhry said that might be true, if you're use cells from an embryo, but there are ethical and technical concerns with that, and even cells from healthy 20-something donors have aged to varying degrees.

It is a promising area of medicine, but far from FDA approval. Plus, even Sampson warns that young donor stem cells should not be seen as a quick fix or a panacea.

"I have to temper expectations and let patients know this isn't magic pixie dust. We're studying this under a clinical trial, and results do take time," Sampson said.

Athletes pioneered this trend

As is often the case with exclusive and experimental therapies, athletes were the real pioneers of this treatment.

A 2014 study found that 12 NFL players, including Peyton Manning , had received stem-cell treatments (not approved by the FDA) to help them bounce back from various injuries. NFL superstar George Kittle , pro wrestler Hulk Hogan, and UFC fighter TJ Dillashaw have all visited the same clinic in Panama for an injection of cells harvested from donated umbilical-cord tissue. (Other athletes have had treatments involving their own stem cells — including tennis great Rafael Nadal for his knee and back, ESPN reported , and golfer Jack Nicklaus for his back pain, according to CNN .)

Sampson is frustrated by the fact that his work is inherently expensive and off-limits because it perpetuates a vicious cycle. If only a few people can do it, there's less opportunity to study how these treatments could help for aging and chronic diseases, he said.

But, in a way, that's why he's effusive about wealthy patients like Johnson and elite athletes who do come through. Those who have a strong interest in longevity and the resources to pursue it are helping to drum up interest in this kind of medicine.

He hopes this buzz will drive research that could someday help treat or prevent multiple chronic conditions.

When stem-cell therapy goes wrong

Research is a slow process, though.

For now, the main impact of this brewing interest is the proliferation of so-called " rogue clinics " in the US and abroad, making bold claims about how their unproven treatments can transform your body.

Done with proper medical oversight, some studies have found no adverse effects from stem-cell treatments for various conditions.

This is a risky arena, though. Botched stem-cell treatments can cause infection, blindness, and excessive cell growth, which can trigger the formation of tumors.

"I've heard horror stories because you go there in desperation and maybe some people will have a benefit, but the vast majority of people don't know what they're getting," Chaudhry said. It can be difficult to know what exactly you're getting, how much, and whether it's been stored and handled safely.

There are also a lot of unknowns about the long-term effects of the procedures, research suggests. Paul Knoepfler, a professor and researcher at UC Davis School of Medicine and the author of " Stem Cells: An Insider's Guide, " told Business Insider that the perceived benefit from stem-cell treatments could be a placebo and may cause patients to miss out on more evidence-based therapies, such as joint replacements.

Johnson said he's not convinced that his approach of taking on experimental, innovative treatments is any riskier than letting nature take its course, especially after he's done his homework. "Something could of course go wrong, but that's just life and something could go wrong anyways," he said. "The risk is a nuanced conversation. It's not clear that this is the higher-risk path. It may in fact be a lower-risk path."

The takeaway: Is stem-cell therapy worth it?

Mattias Bernow, the CEO of the biotech company Cellcolabs, which provided the stem cells for Johnson's procedure, has high hopes for the future of this treatment.

"What I'm really hoping for is that in the future, when we go to the office for the yearly checkup, and we get our flu shot, maybe we'll also get a stem-cell boost either to treat our current conditions or to delay the onset of them, to treat our bodies in the best possible way independently of whatever the genetic lottery gave us," he told BI.

While stem-cell therapies look promising for vision loss or diabetes, experts largely agree that they are probably not a fountain of youth.

More high-quality data is needed to understand how they affect aging. They may not do anything to address more complex consequences of aging, such as neurological degeneration.

"At a more basic level there isn't even really a common sense reason why MSCs would help aging, particularly related to the brain," Knoepfler said. "So far, we just haven't seen clinical trials work out that well for the most part," he added.

If you don't have the cash to fly off for high-tech treatment, though, finding a physical therapist or good personal trainer is a helpful first step to assess your mobility and make an exercise plan to relieve joint pain and prevent injury over time.