Can Young Blood Make You Live Longer?

The science doesn’t need fact-checking as much as the ethics do.



Soooo … I heard Silicon Valley billionaire Peter Thiel, age 48, is using the blood of twentysomethings to stay young.

Actually, he’s not doing that yet. Reportedly, he’s considered receiving blood transfusions from younger people, which he hopes might reverse signs of aging, but he hasn’t actually said anything publicly beyond hint that he might be game.

Wait, is that even possible? Sucking in young blood to make yourself younger?

Let’s back up a few steps. There’s been some exciting, preliminary research in mice that suggests there’s something about young blood. In these experiments, scientists have stitched together a young mouse and old mouse so that their circulatory systems are pumping the same blood through each other’s veins. This makes tissue stronger in the older mice: repairs spinal cord damage, prompts new brain cells to grow, and “even makes their fur shinier,” writes journalist Megan Scudellari for Nature in a great primer on the research’s history.


When these experiments were done in the 1950s, mice sometimes reacted by trying to bite each other’s heads off. It was not great. But in modern experiments, they are carefully selected for compatibility and hang out beforehand, which seems to help. They seem to behave normally while sewn together and can even be separated afterward. The older mice might be healthier for it but as Scudellari writes, “no one has convincingly shown that young blood lengthens lives, and there is no promise that it will.”

You’d have to be physically stitched to another person and receiving their blood for this to work?

No, no, obviously not, though that is the method that’s shown most of the best results in mice. There’s some evidence that repeated injections of plasma will work the same way, too: A 2014 study showed that they improved cognitive function in aging mice. But we would not stitch humans together, no.


Well, what are we doing to humans then?

We’re basically trying to figure out if any of this translates to humans. This is all very preliminary, but there are actually a couple companies trying out various methods of the idea that young blood can reduce disease in older patients. Stanford researcher Tony Wyss-Coray, who has long been stitching together mice, founded a company called Alkahest and is carrying out a clinical trial on 18 people with Alzheimer’s to see if plasma injections can improve their cognitive function—and, if so, which parts of the plasma are doing the work. The general understanding is that the proteins in young blood have some sort of restorative property, though no one quite understands the mechanism that makes young blood useful.


Another company, Ambrosia LLC, founded by a recently minted Stanford MD, is booting up a clinical trial for anyone over 35 who is aging (aka anyone over the age of 35). (It’s this company that attracted the attention of Thiel’s health adviser, though there’s no sign that Thiel himself has enrolled in the trial.)

In the Ambrosia trial, 600 participants will each receive a liter-and-a-half of blood from someone under 25 over the course of a couple days. Before and after the trial, Ambrosia will analyze various measurements of the participants’ health to see if they can assess any change from the infusion.

Where do they get the young blood?

They buy it from blood banks, just like any other hospital would.


OK, I guess that’s not that weird. So, I’d like to live longer. How do I sign up?

Whoa, slow down. This will probably not actually extend people’s lives. It’s not even always effective in mice. In a trial that involved injecting rodents with plasma over the course of 16 weeks, the mice didn’t live any longer than a control group injected with saline. There isn’t enough research done in humans to know if the small benefits to tissue health transfers, and we do know that mice are not perfect foils for the human body.


“There’s just no clinical evidence [that the treatment will be beneficial], and you’re basically abusing people’s trust and the public excitement around this,” Wyss-Coray told Science magazine of the Ambrosia trial. (Yes, his company could be considered a competitor to Ambrosia, though it doesn’t seem like he’s selling anything yet.)


Ambrosia’s founder Jesse Karmazin, on the other hand, tells me that he finds the evidence from mouse studies along with encouraging results from the few small studies that have been conducted in humans, like Wyss-Coray’s, enough to justify his trial.

At any rate, transfusions are very safe when properly supervised, so it’s not like he’s trying some experimental procedure that could do harm. He is, however, charging participants $8,000.

Seems pretty fair for a shot at longer life, no?

Well, normally, in clinical trials, people are paid for their time and participation, not the other way around. This is actually pretty weird. So weird, in fact, that it’s unlikely this trial will result in reputable results able to tell us anything meaningful about blood transfusions.


Taking money from participants is referred to as pay-to-play. While a handful of researchers are trying it, it’s rife with ethical issues, many of which University of Pennsylvania medical ethicist Ezekiel J. Emanuel (and co-authors) outlined in an editorial for Science Translational Medicine last year. (They also noted that the method has been favored by “unscrupulous companies and health facilities” looking to turn a profit.)


The reason why this is suspect is because clinical trials are setup to test a treatment as objectively as possible. In fact, the highest standard of clinical trial is one that is placebo-controlled and conducted double-blind. Participants are recruited based on specific criteria—for example, if they all have a disease and are within a certain age range. These participants are randomly assigned to different groups. One of these groups receives a placebo (a sugar pill instead of a drug), so researchers can understand what changes are attributable to the drug itself and what changes are attributable to the theater of the treatment. Patients are put in these groups randomly: Ideally, neither the patient nor the experimenter knows what kind of treatment they’re receiving.


Isn’t Ambrosia doing that?

Nope. In Ambrosia’s trial, all patients appear to be getting the same treatment—there is no placebo set up, so there is nothing to blind. The thinking is that people shelling out eight grand won’t accept the terms of a randomized treatment, and the possibility of receiving a mere placebo—the very backbone of a good clinical trial.

The terms of enrollment for Ambrosia’s trial are also laughably general. I mean, 35-year-olds aren’t exactly elderly. They aren’t going to have any diseases associated with aging. As Harvard researcher Amy Wagers told Scudellari in Nature last year, most effective use of young blood will probably be for treating a specific disease, or helping elderly recover from surgery. It’s hard to know what kind of measurable effect it might have on a—by all appearances spry—40-something like Thiel.


It also means that Ambrosia’s sample is going to be skewed toward people who are can afford the treatment and who self-select to prioritize youth. There’s no telling how this sample size may compare to the average person.

Maybe it’s not a perfect clinical trial. But won’t the people still get something out of it?

Honestly, who knows! The pay-to-play model is potentially very dishonest: Most clinical trials do not work out. This is how science goes. A clinical trial is an experiment, not a service. When scientists set it up like one, it puts patients in a position to be taken advantage of because the treatment being tested probably will not work.


Hmmm. But this is legal and everything?

Yes, technically it is. Blood transfusions are a common, Food and Drug Administration–approved treatment, and Karmazin has a medical degree, so he can administer them at his discretion.

I asked Karmazin about some criticisms of the pay-to-play model. He wrote in an email that “patients frequently pay for off-label uses of medications, based on physician judgment.” That’s true. But the doctor’s judgement in this case is rather optimistic. The price is also pretty steep.

I think I’m going to sit this one out and see what they come up with.

That seems best.

What else I can do to live longer?

There are a number of actions you can take that have been shown to extend lifespan, such as eating more vegetables, exercising regularly, or not smoking.

Yeah, yeah, I know.