How Can Humans Reverse Aging?
Humans, like all other species, age. But unlike other species, we have the ability to reverse some of its consequences.
For as long as mortality has existed, people have tried to outsmart aging. The Epic of Gilgamesh tells of a plant that makes old men young, and Herodotus wrote of the Fountain of Youth, sending many to fruitlessly seek it in the New World.
1. Embryonic Stem Cells
Embryonic stem cells are a class of undifferentiated cells that exist in multicellular organisms, including humans. These “blank” cells can develop into specialized cells that perform particular functions, such as heart muscle or skin. They can also turn into specialized cells that can regenerate and repair tissues. These stem cells are the foundation of the human body.
During the first week of development, embryonic stem cells are pluripotent, meaning they can give rise to any type of cell in the body. These embryonic stem cells are found in the inner cell mass of a fertilized egg, or blastocyst. After about a week, these cells lose their pluripotency and begin to specialize into different types of cells.
Scientists have been able to culture these embryonic stem cells in the lab, where they can be used for research on the early stages of human development. Embryonic stem cells can also be induced to become specialized cells such as heart muscle cells for use in medical therapies.
In addition, scientists have discovered ways to reprogram mature cells into stem cells without using an actual embryo. This is called reprogramming, and it involves introducing the genes that control the process of cell differentiation into the mature cell. This can cause the mature cell to become pluripotent again. Scientists have also been able to change existing specialized cells into stem cells, such as reprogramming skin cells into heart muscle cells and converting them back into skin.
Stem cells can be obtained from a variety of sources, including bone marrow, blood, amniotic fluid (the sac that surrounds and protects a developing fetus in the uterus), and umbilical cord blood. Stem cells can be injected into damaged tissue to regenerate new cells or replace aging cells. This approach has shown promise in the treatment of certain diseases.
Obtaining embryonic stem cells from actual human embryos is technically difficult and ethically controversial, but it has allowed scientists to study the early stages of development in a dish. It can also be possible to generate cloned stem cells, in which the nucleus of a somatic (body) cell is transferred into an empty fertilized egg that has had its own nuclear DNA removed. The resulting cloned embryo can then be implanted into the uterus and treated like a normal fertilized embryo.
2. Plasma Dilution
When University of California researchers made conjoined twins out of older and younger mice, they found that the blood between the two animals had rejuvenating effects. The resulting discovery, dubbed parabiosis, sparked excitement over the possibility of finding specific proteins that could serve as a fountain of youth for human beings. It also led to the hypothesis that plasma, the liquid component of blood, might contain these beneficial molecules and could be used to reverse aging in other ways, such as when it was combined with stem cells.
Since then, many research laboratories have conducted experiments to identify the “youth factors” in the plasma of young blood and tested whether they could rejuvenate aging tissues in old mice through simple blood exchanges. Several of these studies showed that certain compounds, such as GDF11, could improve brain and heart function, slow down the progression of Alzheimer’s disease, and increase the activity of muscle satellite cells, which are responsible for the repair of damaged tissue.
The latest developments, published in 2020 by the same UC Berkeley lab that made the original parabiosis discoveries, offer more direct support for the idea that the plasma in young blood can have rejuvenating properties. In a first-of-its-kind study, they found that swapping out blood plasma for a neutral solution of saline and albumin (essentially performing a modified form of therapeutic plasma exchange or TPE) reduced biological age by 1.32 years and increased healthspan, the number of healthy years lived without a debilitating disease.
Plasma dilution did more than simply shift the proteomic composition of an individual’s blood; it reset core signaling networks by suppressing inflammation-related pathways, such as JAK-STAT, MAPK/ERK1/2, NF-kB, and Toll-like receptor. These changes indicate that a wide range of organ systems can be rejuvenated through this process alone, without any additional young blood or “youth factors.”
Human studies of this concept are in the early stages, but the results are promising. In a small clinical study, repeated plasma dilution significantly reduced the biological age of participants and boosted their healthspan by about three years. These findings, combined with other evidence — including the restoration of normal levels of key immune parameters, reversal of age-associated DNA damage and cellular senescence in vascular endothelial cells, and normalization of antibody glycosylation patterns — suggest that these rejuvenating effects may be extendable to larger clinical trials and eventually to the general population.
3. Reprogramming Cells
Scientists are able to reprogram cells by artificially adding a set of four genes that turn them into pluripotent stem cells, the kind of cells that can turn into any cell in the body. The process is called cellular reprogramming, and it is one of the most promising avenues in the search for life-extending therapies.
Shinya Yamanaka won the Nobel Prize for discovering cellular reprogramming in 2012. His work enabled researchers to make somatic (non-embryonic) cells into stem cells by forcibly activating certain genes, known as Yamanaka factors. Yamanaka’s work paved the way for scientists to use reprogramming to reverse aging and treat disease.
Cellular reprogramming allows scientists to take readily available cells, such as blood or skin cells, and transform them into any type of cell in the human body, including neurons, liver, heart and bone cells. It is also possible to reprogram a damaged cell to behave like a healthy one. This has the potential to reverse many diseases and conditions, including diabetes, heart disease, neurodegeneration and aging-related cognitive decline.
In recent years, scientists have found a way to increase the efficiency of cellular reprogramming. By using enzymes to untangle reprogramming DNA, scientists can get the cells to change identities much more reliably. This is a major step forward because it means that we will be able to use repurposed cells to treat diseases such as Parkinson’s.
Scientists have used reprogramming to revert a number of aging hallmarks in mice, such as degeneration of the retina and kidney, and they have also shown that it can prevent certain diseases from developing. For example, Salk Institute scientists reprogrammed cells from aged mice to become neurons and restored their vision, and scientists at Rejuvenate Bio have used reprogramming to extend the lifespan of naturally aged mice.
Rejuvenation science is making rapid progress and attracting investment. Several big companies, such as Google’s Calico and Altos Labs backed by billionaire Sam Altman, are focused on rejuvenation research. With these advances and a renewed interest in the longevity industry, it is likely that rejuvenation biotech will explode in the next few years.


