A study in the 50’s concluded if two rats (one old, and one young) shared the same circulatory system the old rat would get younger, and the younger rat would get older. This process is called parabiosis. The study below looks at parabiosis again, but this time with an infusion of young plasma. It used six different biological clocks to assess the discrepancy between biological age and chronological age. As you age your DNA changes and we are now able to measure these changes.

In the study they found that a young plasma infusion reversed aging according to the biological clocks. Furthermore, they noted that organ function seemed to improve with the young plasma infusion.

The study from the 50’s was repeated at Stanford University from 2005 through 2010 with an effort to search for what it is in blood or plasma that rejuvenates. A number of groups feel that they have isolated the relevant compound, but testing has so far been inconclusive, or is too early to definitively have a read out. To date we do not know what the active agents are, and whether it is reproducible in humans.

Reversing age: dual species measurement of epigenetic age with a single clock | bioRxiv

https://www.biorxiv.org/content/10.1101/2020.05.07.082917v1.full