Young blood transfusion refers to transfusing blood specifically from a young person into an older one with the intention of creating a health benefit. The scientific community currently views the practice as essentially pseudoscientific, with comparisons to snake oil. There are also concerns of harm. The U.S. Food and Drug Administration, in 2019, cautioned "consumers against receiving young donor plasma infusions" stating that they are an "unproven treatment".
Experiments at Stanford University on pairs of old and young rodents placed into parabiosis suggest that the circulation of blood from young mice seems to invigorate older mice. Parabiosis experiments are difficult to generalize, as the circulatory systems of the mice are fully joined and it is unclear whether the benefits come from the sharing of blood or the older mouse's access to the younger mouse's organs. A study conducted at UC Berkeley found that blood from older mice hurt younger mice, while older mice were not benefited by the blood of younger mice.
In experiments like this, researchers found that some of these mice died quickly (11 out of 69 in one experiment) for reasons the scientists could not explain, but described as possibly some form of rejection. Amy Wagers, a researcher who coauthored several mouse studies on young blood transfusion, has said that her papers do not provide a scientific basis for some of the existing human trials.
Evidence from two large studies in 2017 showed that the transfusion of blood from younger donors to older people led to outcomes that were either no different from, or led to worse outcomes than, blood from older donors. Research on blood transfusion outcomes has been complicated by the lack of careful characterization of the transfusion products that have been used in clinical trials; studies had focused on how storage methods and duration might affect blood, but not on the differences among lots of blood themselves.
In the early 2000s a group of scientists at Stanford University, California, revived a grisly procedure used in the 1950s known as parabiosis. They paired living mice, young with old, peeled back their skin and stitched together their sides so the two animals shared the same blood circulatory system. A month later, they found signs of rejuvenation in the muscles and livers of the old mice. The findings, published in 2005, turned the minds of scientists, entrepreneurs and the public to the potential of young blood to rejuvenate ageing people. By 2016, enough interest had grown to prompt a US-based startup called Ambrosia to start offering pricey infusions of young plasma – the cell-free component of blood. The procedure came under fire from the US Food and Drug Administration early last year both for its lack of proven clinical benefit and for potential safety issues; Ambrosia closed, though it has recently reopened.
Meanwhile, a clutch of scientific startups are trying to discover the secrets of parabiosis and use them to tackle age-related disease. By identifying factors in plasma that change with age, they aim to create therapies that either supplement what’s beneficial in young blood or to inhibit what’s detrimental in old. One is even beginning to report early clinical trial results.
“There’s still a long way to go – blood is complicated,” says Aubrey de Grey, who leads the nonprofit Sens (strategies for engineered negligible senescence) Research Foundation. “But there are many excellent labs focused on this, so I am optimistic about progress.”
While no one thinks that altering one or more blood factors will be the sole answer to slowing or reversing ageing, blood has the potential advantage of cutting across various ageing mechanisms, allowing several of them to be modulated at once.
Experiments beginning in the 1950s in the Cornell University lab of Clive McCay on pairs of old and young rodents placed into parabiosis provided some evidence, albeit limited and "largely anecdotal", that the circulation of blood from young mice increased both the longevity and the tissue function of old mice. After decades in which relatively little work on parabiosis in aging was done, the work was revived by researchers at Stanford University and the University of California at Berkeley. Parabiosis experiments are difficult to generalize, as the circulatory systems of the mice are fully joined and it is unclear whether the benefits come from the sharing of blood or the older mouse's access to the younger mouse's organs. A study conducted at UC Berkeley found that when delivered alone, blood from older mice was more inhibitory to the regenerative capacities of younger mice than blood from younger mice was beneficial to older ones, and that the benefit of young blood in older mice was than had been observed when older mice were subjected to parabiosis.
A review of studies on donor age for whole blood transfusions reported that blood from donors under the age of 20 years, when compared to donors aged 20–60 years, resulted in a modestly higher risk of death in the recipients.However, other studies have found no effect of age. Research on blood transfusion outcomes has been complicated by the lack of careful characterization of the transfusion products that have been used in clinical trials; studies had focused on how storage methods and duration might affect blood, but not on the differences among lots of blood themselves.