Human Hibernation: Myth or Science?

Human hibernation is a technology that until a few years ago was considered science fiction, but recent advances and applications have brought it back into the limelight, raising hopes in the medical field but also skepticism. Technically, human hibernation consists of suspending the vital functions of the human body, keeping it in a state of suspended animation, in order to allow for the maintenance of life or the resumption of biological function in the future. This is achieved by lowering the body temperature to preserve it from natural degradation. The idea of human hibernation dates back at least a hundred years, when the American writer Edward Page Mitchell published a story about cryostasis, imagining a machine capable of indefinitely slowing down the body's metabolism almost to a halt, only to be brought back to normalcy in the future. Since then, terms like cryostasis, cryogenesis, hibernation have entered books, films, and TV shows, keeping alive the public imagination and raising questions about its feasibility.
To be honest, nature itself offers examples of slowed metabolism, such as hibernation in some species of mammals (from bears to marmots) or certain frogs that effectively "freeze" during the winter to wake up in the spring. Although with different methods, all of these animals carry out a slowing down of vital functions, which is why studies have so far been based on the idea of slowing down or suspending the fundamental biological processes of the body. However, it should be said that despite the great interest and fascination it arouses, human hibernation has not been designed natively by nature and therefore represents a relatively recent and still unexplored field of research. The first step was to develop techniques for the cryopreservation of organs, a technology used today to preserve biological tissues taken from donors, pending their transplantation. However, these techniques cannot yet be applied to the entire body, as the freezing process itself causes significant damage to biological tissues, namely the formation of ice crystals that damage cells, blood vessels, fibers, and so on. To avoid this, various solutions have been experimented with, such as partial cryopreservation, or the replacement of blood with solutions (mostly saline) that prevent the formation of the already mentioned dangerous ice crystals (similar to how the frog produces a glucose-based solution that prevents tissues from being damaged during the process). However, these techniques are not yet applicable on a large scale, as they are only suitable for some organs, but only up to a certain temperature, otherwise, the organ itself is damaged: for example, our brain contains hundreds of millions of micro-blood vessels for which there is no proven technology yet to preserve them at the necessary temperature for the cryostasis process. This means that even if the body were to be hibernated, the damage suffered during this period could have an irreversible effect that may impair its awakening. Therefore, examining the current situation, it is reasonable to deduce that human hibernation is not yet ready to be used on ordinary people. Nevertheless, science is making significant progress in recent years, so much so that there are already companies worldwide that offer a cryostasis service (seen as an alternative to end-of-life) and in the future, new technologies could be discovered that are able to bring back to life those who have undergone such treatment.

Myths and realities of cryopreservation:
Cryopreservation, the technology that underpins human hibernation, is often subject to myths and prejudices. One of the main myths concerns the preservation of the brain after death. Some people have signed agreements for the preservation of their own brain, hoping to be able to resume their life in the future once hibernation technology becomes mature. However, as mentioned before, science does not support this idea. Cryostasis causes damage to brain tissues, which are considered irreversible. The cryopreserved brain would then inevitably be compromised, making it impossible to restore the biological functions essential to life. Another myth concerns the belief that any organic tissue can be "switched off" like a light switch. In reality, during hibernation, no tissue is completely inactive, only slowed down: in fact, most tissues are very sensitive to oxygen deprivation, and the slowing down of brain function during hibernation can cause permanent damage to cells. This is why even the current processes of cryostasis of individual organs have some limitations: for example, it is not yet possible to cryopreserve large organs for long periods.

Advances in cryopreservation technology:
At the same time, there is great scientific interest in human hibernation, which has led to innumerable advances in recent years that can be considered significant steps forward in research. As mentioned before, many researchers are experimenting with the use of compounds called "cryoprotectants", which prevent the creation of crystals: first and foremost the already mentioned saline solution that replaces the water present in biological tissues with a compound that prevents the formation of ice crystals, thus limiting damage to tissues. Another approach to cryopreservation is based on the use of biological glass. In this case, biological tissues are replaced with a solid substance similar to glass, which prevents the formation of ice crystals. This technology presents multiple challenges, but it represents a promising approach. A third technology that can be used to reduce body damage during hibernation is based on the idea of replacing blood with cryogenic replacement solutions. This approach is based on the suspension of the respiratory and circulatory function of the body, thus reducing the amount of damage caused during hibernation. However, the use of such expedients presents several limitations, above all the toxicity that can cause damage to biological tissues and health in the high concentrations required to cryopreserve the entire body, despite being an essential first step towards the development of cryopreservation techniques that can avoid the formation of crystals. It is hoped that in the near future, possible side effects on health will be studied and reduced.

Scientists' attempts on animals:
In recent decades, scientists have experimented with hibernation in animals, with mixed results. For example, some researchers have studied animals that actually freeze (like some species of frogs) which are able to hibernate at temperatures below zero Celsius, only to return to their normal functions once their nominal biological parameters have been restored. However, these animals are vastly different from human beings, so much so that the ultimate example in large mammals is hibernation, which is quite different from a sub-zero hibernation, being effectively a "slowed deep sleep" rather than a genuine cryostasis. Therefore, while these studies are a starting point, they do not provide definitive proof of the feasibility of human hibernation.

Are cryopreserved people just "new mummies" or is there an actual possibility of awakening?
This question does not currently have an answer, but it does give us hope due to the enormous scientific knowledge that has been gained in recent decades: as technology evolves, new hopes emerge, especially for patients with incurable diseases today, who could be placed in a state of hibernation until suitable cures are developed. This is why some companies offer cryopreservation services in case of death, from the preservation of the brain or other biological tissues, to the whole body. Some US non-profit associations such as the Cryonics Institute, the Life Extension Foundation and the Alcor Life Extension Foundation, as well as the Russian Kriorus, are currently the main organizations offering cryopreservation services. On the other hand, what cannot be accomplished by today's science could be achieved by that of tomorrow, including awakening from conditions and problems currently considered insurmountable.