William Hartnell (1908 - 1975, center) stars as the doctor alongside Dracula and Frankenstein's monster in "The Chase," an episode of the long-running television series "Doctor Who."
William Hartnell (1908 - 1975, center) stars as the doctor alongside Dracula and Frankenstein's monster in "The Chase," an episode of the long-running television series "Doctor Who." - 
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Are we on the path to achieving immortality? Eh, not quite. But there is a potentially promising new medical procedure that could help alleviate the effects of aging, and it involves harvesting young blood.

The practice of parabiosis — which involves stitching two animals together so that their circulatory systems are intertwined  — has been shown to have some rejuvenating effects on mice. While testing on humans hasn't gone that far, some companies are taking on this concept by offering people blood transfusions. 

Tim Cross, science correspondent for the Economist Magazine, joined us to talk about the practice and how effective it is. Below is an edited transcript.

David Brancaccio: So the TV show "Silicon Valley" has joked about it. Your piece says we should not mention vampires, but there's some interesting animal evidence that sharing a circulatory system with a younger creature helps the older creature.

Tim Cross: That's right. I mean, it's based on this sort of slightly gruesome set of experiments you can do where you basically take two lab animals — mice or rats or whatever  —you sort of wound them, and you stitch them together in such a way at the site of the wound that as they heal, their circulatory systems kind of merge. And it turns out if you do this with one mouse being young and one mouse being old, you can get some quite impressive rejuvenatory effects in the old mouse.

Brancaccio: All right, so they're taking a look at if what we've discovered in animals might be in some way applicable to human beings?

Cross: There are at least a couple of companies who've jumped right into doing human trials. So there's one called Alkahest, which is looking at whether this might work for people with Alzheimer's disease, because some of the mouse results showed that one of the things that gets better is sort of mental capacity.

Brancaccio: There's also an interesting — call it a clinical trial — experiment in which the participants actually pay to be in the trial. Normally it's the other way around with a with a trial.

Cross: This is another company called Ambrosia, and you have to pay $8,000 to take part. Anyone over 35 can pay to take part. You get blood transfusions from somebody under the age of 25. A lot of the time with these trials, they'll give some people the treatment and some people something called a placebo. Ambrosia said they aren't going to do that, because they don't think that having asked people to pay $8,000 for this treatment, they can risk them getting a placebo. So that's caused, I guess, some sort of raised eyebrows among the researchers who look into this stuff for a living.

Brancaccio: All right, so we should emphasize though they're doing the basic science here. This is not something that's close to being a treatment that might be available in a more widespread way.

Cross: It seems to work in the lab on on mice. It doesn't necessarily always work. If you try and do something that's a bit closer to blood transfusions  — because obviously you don't want to be thinking about stitching human beings together — it seems to do something, but doesn't have quite the same level of benefits as the sort of full-on treatment does. I think these human trials are kind of a shot in the dark. I mean, it may be that they work, but I think you know it would be kind of impressive if they did.

Brancaccio: You just need to assure me that youngsters are not going to have to get grafted onto an old venture capitalist. 

Cross: That's not any plan I want to be part of — put it that way.

Follow David Brancaccio at @DavidBrancaccio