Cryosleep: How close are we to reviving the dead?
Key Takeaways
Contrary to popular belief, cryosleep is not suspended animation but a form of deep sleep called torpor, which significantly slows metabolic functions.
Cryopreservation has shown promise in animals, but current technology hasn’t been able to translate these successes to humans.
While we are still far from being able to revive cryopreserved human bodies, cryonics has shown promising results in preserving and reviving organisms from the animal kingdom like tardigrades.
For over half a century, futurist movies have depicted cryogenic preservation as a means to revive the dead and potentially achieve interstellar travel.
The idea materialized in 1967 when American psychologist James Hiram Bedford became the first person to be cryogenically frozen after his death. Robert Ettinger, known as "the father of cryonics" and founder of the Cryonics Institute, also chose cryopreservation for himself and his family.[]
Despite these early efforts, we are still far from being able to revive cryopreserved bodies. Nevertheless, the interest in cryonics has grown, with notable figures like PayPal co-founder Peter Thiel expressing a desire to be cryogenically frozen after death.
Advances in cryonics
Cryonics, derived from the Greek word for "cold," involves preserving a human corpse or brain at extremely low temperatures to slow metabolic processes drastically—in a state of deep sleep known as cryosleep. Bodies are stored in containers filled with liquid nitrogen, cooled to -150°Celsius.[]
While we are still far from being able to revive cryopreserved human bodies, we have promising results from the animal kingdom showcasing cryonics' potential to preserve complex life forms.
In 2016, Japanese researchers revived two tardigrades—eight-legged microscopic animals also known as water bears—that had been frozen for over 30 years.[]
Ongoing research aims to bring back a 42,000-year-extinct woolly mammoth using cryonics. Discovered in 2013 in the Siberian permafrost, this well-preserved specimen is being studied to edit its genes and combine them with those of the Asian elephant.[]
Current roadblocks
Feasibility
Cells are made up of water, and what happens when you freeze water? It expands causing irreversible damage. The Cryonics Institute addresses this by replacing blood with an antifreeze solution to prevent ice crystal formation. This process, known as vitrification, preserves cell structures by turning tissues into a solid mass similar to glass.[]
Cost of cryopreservation
Cryopreservation is also costly. Despite increasing interest, maintaining preserved bodies is financially challenging. Furthermore, there is no conclusive evidence that antifreeze solutions can effectively preserve delicate nervous and circulatory systems.
According to Clive Coen, a professor of neuroscience at King’s College London, dense brain tissues cannot be adequately protected by antifreeze, and some neurons may already be irreversibly damaged by the time a cryonics team arrives.[]
While the revival of humans from cryosleep remains uncertain due to current technological limitations, cryobiology—the science of how organisms and tissues interact with low temperatures—is already being used for the management of many diseases.
Current applications of cryobiology
Therapeutic hypothermia
Therapeutic hypothermia, akin to the torpor state (deep sleep) seen in hibernating animals, is a well-established medical technique.
It slows down cellular biochemical reactions, enhancing cellular survival. It is neuroprotective by inhibiting excitotoxicity, apoptosis, neuroinflammation, free radical generation, seizures, and blood-brain barrier disruption.[]
Patients are cooled using ice packs, chilled pads or blankets, and cold intravenous saline. While normal body temperature is about 37°C, therapeutic hypothermia reduces it to 32°C to 34°C.[]
This technique dates back to ancient times, with Hippocrates reportedly using snow to slow blood flow in wounded soldiers. In the 1800s, cryoanalgesia was used for pain management during amputations and to reduce blood loss.[] Today, therapeutic hypothermia is primarily used to improve neurological outcomes and survival rates in comatose survivors of cardiac arrest.
One pioneering trial conducted in Melbourne enrolled 77 patients with cardiac arrest, who were divided into normothermia and hypothermia groups. The hypothermia group cooled to 33°C and showed significantly higher rates of favorable outcomes compared to the normothermia group.[]
Another European study also found better neurological outcomes and lower mortality in the hypothermia group. However, higher rates of complications were noted, possibly due to extended cooling durations.[]
A 2024 study from the Journal of Perinatology established the safety and efficacy of therapeutic hypothermia for managing neonatal encephalopathy in both term and preterm infants.[]
Cryostimulation
Cryostimulation—cold exposure in healthy individuals—is being widely used in sports medicine for faster healing of injuries. It is also anecdotally reported to benefit patients with metabolic disorders, multiple sclerosis, affective disorders, cognitive dysfunction, poor sleep quality, chronic back pain, and fibromyalgia.[] However, its mechanisms remain unclear.
Cryostimulation can be achieved through whole-body cryotherapy (WBC) or partial-body cryotherapy (PBC). WBC involves stepping into cryochambers with temperatures from -50°C to -150°C, while PBC uses cryosaunas with air and liquid nitrogen at around -190°C.[]
Key differences between WBC and PBC include PBC not exposing the head, using nitrogen vapor for cooling vs refrigerated air in WBC, and differences in device size and mobility. PBC exposes participants to both cold and hypoxia, potentially triggering different cellular responses compared to cold alone. Additionally, cryosaunas have less temperature uniformity than cryochambers.[]
Despite its popularity, there is no convincing evidence of the long-term benefits. The FDA recently warned consumers that, “The US Food and Administration has not cleared or approved any whole body cryotherapy devices” and highlighted incidents of adverse reactions and fatalities related to cryotherapy.[]
As stated in a commentary from the Canadian Medical Association, as “it is illegal to perform cryonics on a person who has yet to be pronounced dead by a qualified physician,” the success of future cryopreservation will depend on not only reviving the preserved body but also reversing the damage from the cause of death, whether it’s aging or a fatal illness.[] If future technology can cure currently incurable diseases and achieve rejuvenation, cryonics could be successful.
What this means for you
Cryogenic sleep may one day make interstellar travel feasible and offer a lifeline to terminally ill patients, but we are still far from realizing its full potential. For now, therapeutic hypothermia and cryotherapy offer valuable applications in medicine, keeping the dream of cryonics alive for future generations.