Back in medieval times they used to bleed people. What if they were right?
In the early 2000's US scientists tried connecting an old mouse up to a young mouse. Surgically- by joining the blood vessels.
As the new Siamese Twins shared their blood, the young one got older, and the old one--- got younger. This was thought to be impossible at the time, making something younger.
But that isn't the crazy idea yet.
At first the idea that there might be something in young blood that stopped ageing took off. This is the perpetual thinking of the Pharmaceutical Industry- find something to sell.
Some individuals got convinced:
www.vanityfair.com
Yep, if you have the resources, you can try anything.
Unfortunately for creepy old billionaires, but probably good for everybody under 25, this idea didn't pan out. Vampirism isn't real.
Bummer for anyone who is thinking about staking some billionaires. I mean - with a stake. The idea began to lose steam.
www.theverge.com
So... why did that mouse get younger?
Well it seems that it's OLD blood that makes things get older. ( hence, that young mouse everybody forgot about)
The obvious idea is now obvious. What happens if you take an old person, and change out their blood completely? Well they would die, of course, nobody survives having all their blood taken out. No red cells to move oxygen around.
Well there's some good news. The red cells don't affect ageing. It's the liquid they are in.
We can keep the cells, just change out the liquid, which is possible by a series of dilutions. So has anybody been crazy enough to try this?
Yes.
www.ncbi.nlm.nih.gov
Last year when everybody was only reading about lockdowns, pandemics and new regulations, Irina Conboy and her team managed to pull off this stunt in mice.
The mice got younger.
By Christmas, 2020, people were starting to try it themselves. On themselves.
www.fightaging.org
Here are the results from a related trial:
link.springer.com
The effect is partially due to albumin's property as an antioxidant. You know how they say a vitamin C tablet is a good antioxidant? Imagine having gallons of the stuff circulating instead, in place of inflammatory old plasma. It reverses the biological age, according to this study:
www.biorxiv.org
In the early 2000's US scientists tried connecting an old mouse up to a young mouse. Surgically- by joining the blood vessels.
As the new Siamese Twins shared their blood, the young one got older, and the old one--- got younger. This was thought to be impossible at the time, making something younger.
But that isn't the crazy idea yet.
At first the idea that there might be something in young blood that stopped ageing took off. This is the perpetual thinking of the Pharmaceutical Industry- find something to sell.
Some individuals got convinced:

Peter Thiel Wants to Inject Himself With Young People’s Blood
The Silicon Valley billionaire reportedly sees blood transfusions as the pathway to radical life extension.
Unfortunately for creepy old billionaires, but probably good for everybody under 25, this idea didn't pan out. Vampirism isn't real.
“I think it will take some time for people to really give up the idea that that young plasma contains rejuvenation molecules, or silver bullets, for aging,” said Dobri Kiprov, a medical director of Apheresis Care Group
Bummer for anyone who is thinking about staking some billionaires. I mean - with a stake. The idea began to lose steam.

Everything wrong with the young blood injection craze
This story has real science, overgeneralized results, lots of high hopes, and people trying to make a quick buck

Recently, the US Food and Drug Administration made a somewhat strange request: please don’t buy transfusions of young blood plasma to improve your health. The announcement is a conclusion of sorts to years-long hype over the tantalizing possibility that the fountain of youth can be found in the bodies of other people.
So... why did that mouse get younger?
Well it seems that it's OLD blood that makes things get older. ( hence, that young mouse everybody forgot about)
The obvious idea is now obvious. What happens if you take an old person, and change out their blood completely? Well they would die, of course, nobody survives having all their blood taken out. No red cells to move oxygen around.
Well there's some good news. The red cells don't affect ageing. It's the liquid they are in.
We can keep the cells, just change out the liquid, which is possible by a series of dilutions. So has anybody been crazy enough to try this?
Yes.
Rejuvenation of three germ layers tissues by exchanging old blood plasma with saline-albumin - PMC
Heterochronic blood sharing rejuvenates old tissues, and most of the studies on how this works focus on young plasma, its fractions, and a few youthful systemic candidates. However, it was not formally established that young blood is necessary for ...

Last year when everybody was only reading about lockdowns, pandemics and new regulations, Irina Conboy and her team managed to pull off this stunt in mice.
The mice got younger.
By Christmas, 2020, people were starting to try it themselves. On themselves.

Self-Experimenters Make an Initial Attempt at Human Plasma Dilution
Today's news from the self-experimentation community notes a more adventurous effort, in which a few volunteers underwent blood plasma dilution followed by assessments of function. Plasma dilution, or neutral blood exchange, involves extracting blood, replacing the plasma fraction of that blood...

By now, if you know me, you will realise that this is zero impediment for me. But No, I didn't. Waiting to see results first.For most people this procedure is past the outer limits of practicality as a self-experiment. It requires a good amount of scientific or medical knowledge, familiarity with the latest research on the topic, and cooperative physicians.
Here are the results from a related trial:
Matches the mouse results:This trial suggests that Plasma Exchange with albumin replacement could slow cognitive and functional decline in Alzheimer's Disease, although further studies are warranted.

Plasma dilution improves cognition and attenuates neuroinflammation in old mice - GeroScience
Our recent study has established that young blood factors are not causal, nor necessary, for the systemic rejuvenation of mammalian tissues. Instead, a procedure referred to as neutral blood exchange (NBE) that resets signaling milieu to a pro-regenerative state through dilution of old plasma...

The effect is partially due to albumin's property as an antioxidant. You know how they say a vitamin C tablet is a good antioxidant? Imagine having gallons of the stuff circulating instead, in place of inflammatory old plasma. It reverses the biological age, according to this study:

Reversing age: dual species measurement of epigenetic age with a single clock
Young blood plasma is known to confer beneficial effects on various organs in mice. However, it was not known whether young plasma rejuvenates cells and tissues at the epigenetic level; whether it alters the epigenetic clock, which is a highly-accurate molecular biomarker of aging. To address...
The treatment more than halved the epigenetic ages of blood, heart, and liver tissue. A less pronounced, but statistically significant, rejuvenation effect could be observed in the hypothalamus. The treatment was accompanied by progressive improvement in the function of these organs as ascertained through numerous biochemical/physiological biomarkers and behavioral responses to assess cognitive functions. Cellular senescence, which is not associated with epigenetic aging, was also considerably reduced in vital organs. Overall, this study demonstrates that a plasma-derived treatment markedly reverses aging according to epigenetic clocks and benchmark biomarkers of aging.