Can Young Blood Really Rejuvenate the Old?

Research in mice seems to suggest it can

THE vampire jokes write themselves. In the past few years a steady trickle of scientific papers has suggested something straight out of an airport horror novel: that the blood of young animals, infused into the old, has rejuvenating effects. Scientists are excited enough that at least two clinical trials are currently running in humans. But is it true? And if it is, how does it work?

The answer to the first question seems to be a qualified yes, at least in animals. The rejuvenating effects are seen when lab mice are joined together in a rather gruesome procedure called parabiosis. That involves making cuts in the skin of two animals, then suturing them together at the site of the wound. As the cuts heal, the pair’s blood vessels will grow together and merge. The result is two animals that share a circulatory system, with both hearts pumping both sets of blood around both bodies. Doing this with an old mouse and a young mouse has some spectacular effects. As with humans, old mice have a harder time healing from injuries. But link an old mouse to a young one and it becomes able to repair muscle injuries nearly as well as its younger counterpart. Similar benefits are seen in liver cells and the nervous system. And it works in reverse, too: old blood can have a decrepifying effect on the young.

Exactly how this all works is much less clear. The best guess is that some combination of hormones, signalling factors and the like in the…

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