The team detected that the levels of carcinoembryonic antigens fell by around 20 per cent in the blood of people who received the treatment. However, there was no control group or placebo treatment in the study, and it isn’t clear whether a 20 per cent reduction in these proteins is likely to affect someone’s chances of developing cancer.

Karmazin says the team also saw a 10 per cent fall in blood cholesterol levels. “That was a surprise,” he says. This may help explain why a study by a different company last year found that heart health improved in old mice that were given blood from human teenagers.

They also report a 20 per cent fall in the level of amyloids – a type of protein that forms sticky plaques in the brains of people with Alzheimer’s disease. One participant, a 55-year-old man with early onset Alzheimer’s, began to show improvements after one plasma treatment, and his doctors decided he could be allowed to drive a car again. An older woman with more advanced Alzheimer’s is reportedly showing slow improvements, but her results have not been as dramatic.

Although the idea has been around since at least the mid-18th century, science fiction Grandmaster Robert Heinlein made good use of it in his classic 1941 novel Methuselah's Children:

"Yes, yes," agreed Hardy. "Naturally-but what is the basic process?"
"It consists largely in replacing the entire blood tissue in an old person with new, young blood. Old age, so they tell me, is primarily a matter of the progressive accumulation of the waste poisons of metabolism. The blood is supposed to carry them away, but presently the blood gets so clogged with the poisons that the scavenging process doesn't take place properly. Is that right, Doctor Hardy?'
"That's an odd way of putting it, but-"
"I told you I was no biotechnician."
"-essentially correct. It's a matter of diffusion pressure deficit-the d.p.d. on the blood side of a cell wall must be such as to maintain a fairly sharp gradient or there will occur progressive autointoxication of the individual cells. But I must say that I feel somewhat disappointed, Miles Rodney. The basic idea of holding off death by insuring proper scavenging of waste products is not new-I have a bit of chicken heart which has been alive for two and one half centuries through equivalent techniques. As to the use of young blood-yes, that will work. I've kept experimental animals alive by such blood donations to about twice their normal span-" He stopped and looked troubled.
"Yes, Doctor Hardy?"
Hardy chewed his lip. "I gave up that line of research. I found it necessary to have several young donors in order to keep one beneficiary from growing any older. There was a small, but measurable, unfavorable effect on each of the donors. Racially it was self-defeating; there would never be enough donors to go around. Am I to understand, sir that this method is thereby limited to a small, select part of the population?"
"Oh, no! I did not make myself clear, Master Hardy. There are no donors."
"Huh?'
"New blood, enough for everybody, grown outside the body-the Public Health and Longevity Service can provide any amount of it, any type."

After learning about the method, Lazarus Long talks with Andy Libby about it:

They were both silent for a long time, with no need to talk. Presently Lazarus said, "Andy-"
"Yeah?"
"Are you going to look into this new-blood-for-old caper?"
"I suppose so, eventually."
"I've been thinking about it. Between ourselves, I'm not as fast with my fists as I was a century back. Maybe my natural span is wearing out. I do know this: I didn't start planning our real estate venture till I head about this new process. It gave me a new perspective. I find myself thinking about thousands of years-and I never used to worry about anything further ahead than a week from next Wednesday."

Well, dear reader - are you going to try it?