Cryonicist's Horizons

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Hibernation vs Cryopreservation

Find out the differences and similarities of these two procedures, as well as their uses in medicine.

If you are new to biostasis (aka cryonics), you may find it hard, at first glance, to understand all the lexicality. For example, some confusion may arise regarding the differences between hibernation and cryopreservation, not to mention suspended animation or vitrification. Is a hibernated human being in any way similar to a cryopreserved or vitrified human being? While these terms have a lot in common, first and foremost the use of cold temperatures, many aspects also differentiate them. If you want to eventually become an expert cryonicist, check out this article and find out how hibernation and cryopreservation work.

frozen plant
Nearly all plants go dormant when temperatures are low. During dormancy, growth stops and the plant remains in a state of rest until good growing conditions return.


What exactly is hibernation? If you have some memories from your school days, you may remember that some animals, like chipmunks and bats, hibernate. They go into what is usually described as a long “deep sleep” in order to reduce their metabolism. This way, they cut down their need for food (that is less available in winter) and survive until the temperatures rise again.

Now, hibernation is a bit more complicated than this. First of all, hibernating is not sleeping - there is in fact no resting nor dreaming while hibernating. The body temperature is too low to produce the electric currents related to dreaming. Additionally, after hibernation, many animals exhibit signs of sleep deprivation. They will need to sleep a lot over the next few days to recover. Secondly, it doesn’t happen only in winter. Some animals undergo what is called aestivation, lowering their metabolic rate when the temperatures are too hot and/or dry. Finally, whereas the total hibernation period can be several months long, it is not an ongoing process. Most hibernating animals in fact wake up every few weeks to have a snack and get rid of their waste.

But, how exactly can some animals naturally lower their body temperature and slow down their metabolism? And are humans able to do it as well?

How hibernation works

Hibernation is a survival behavior. When the food supply reduces and temperatures become more rigid, animals react to it by migrating to a warmer place or hibernating. There are several factors that trigger hibernation. Some animals have an internal biological calendar (circannual rhythms) that tells them when to hibernate. Others are triggered by the shortening of daytime (photoperiodism). Others react to the diminution of available food.

Once triggered, the animals start preparing a den or a cave. Meanwhile, they collect nonperishable food. Many animals stuff themselves with food, creating a solid supply of fat that will be used while they are hibernating.

When the time comes, their endocrine system activates some specific processes. Glands start releasing altered levels of hormones, controlling every physiological aspect of hibernation. The thyroid, the gland that controls metabolism, reduces metabolic activity. The pituitary, on the other hand, slows down the heartbeat and respiratory rate and several other vital functions. During hibernation, the heart rate drops to as little as 2.5 percent of its usual level. For example, a chipmunk's heart rate slows to five beats per minute from the usual 200. The need for oxygen and breathing rate drops by 50 to 100 percent. Some animals, including many reptiles, stop breathing completely. Moreover, their consciousness is greatly diminished. Most hibernating animals are completely oblivious of their surroundings and can’t easily wake up.

hibernation bear
Bears don’t actually hibernate but enter a state called torpor - which can last for more than 100 consecutive days. During that time, their urine is turned into protein

Use in medicine

Many animals undergo this process, yet there is no human being who can naturally enter a state of hibernation. Nevertheless, a state of artificially induced hibernation (called suspended animation) can bring enormous advantages in the medical field. Likewise, simply lowering the temperature and metabolic rate by a few degrees can, in some cases, save lives.

Let's take a look at some possible applications:

  • Therapeutic hypothermia is a treatment currently used in some hospitals to reduce damages connected to cardiac arrests and strokes. When the heart stops beating, the tissues (like the brain) get damaged because of the lack of oxygen. By lowering the body temperature in a controlled environment, they can reduce the rate of consumption of oxygen and ATP (adenosine triphosphate) demand. This way, they have more time to get the heartbeat going before the damage kicks in.
  • Although hibernating animals do not move for extended periods of time, they do not experience muscle atrophy. Several studies are trying to understand how they manage to minimize loss of muscle mass. This discovery could help treat muscle disorders and help patients who are bedridden for long periods.
  • Likewise, understanding the lack of bone deterioration in hibernating animals, even after long sedentary periods, could lead to new ways of treating degenerative bone diseases, like osteoporosis.
  • Induced suspended animation could help treat cancer. The lowered metabolic rate could slow down the spread of tumors inside their tissues, giving the doctors more time to treat the patient. At the same time, by reducing healthy cells' need for oxygen, it would allow the use of higher doses of chemotherapy. This would be fatal for non-hibernated patients.


Now, human cryopreservation (aka biostasis) is a bit of a different topic. As hibernation, cryopreservation allows the reduction of metabolic rate. Yet, cryopreservation goes a step further, to the point it completely pauses any biological activity. The result is that, while during hibernation the body still needs a lowered amount of energy, during cryopreservation it doesn’t. On the one hand, the cryopreserved person can be kept in this condition for an indefinite time. On the other hand, as there is no activity, an external force will eventually be needed to reactivate metabolic activity and vital functions.

From a biological point of view, biostasis is quite different from hibernation. In fact, no hormonal activity is needed to initiate the process. The procedure must be activated by a third party (usually trained members of a standby team) after the declaration of legal death. Heartbeat and natural respiration will therefore already have stopped. The standby team lowers the body temperature while replacing the body fluids with cryoprotective agents. By doing this, the body enters an amorphous glass-like state where all biological processes are paused. All cells are paused and degradation is interrupted, awaiting possible future revival.

Why cryopreservation is not freezing

Cryopreservation and freezing are two different processes - and one of the main aims of the former is to prevent the latter from happening. In fact, during freezing, the water contained in the tissues freezes, forming ice crystals. These have sharp edges, which damage the tissue. Once thawed, the tissue becomes mush.

As the ultimate aim of cryopreservation is later revival, a tissue in pulp is the last thing one wants to achieve. To prevent this, the fluids in the body are replaced with cryoprotectants (basically, antifreeze substances). The body is vitrified and the cells reach an amorphous glass-like state.

In nature, there are animals such as the Alaskan wood frog that freeze for about 7 months during the winter. Their bodies produce a natural antifreeze, which prevents the formation of ice crystals and enables them to thaw and “come back to life” as soon as temperatures become more bearable. Unfortunately, we humans are not able to produce this substance naturally (at least not with current technology).

ice formation
Ice formations have sharp edges

Possible life saving procedure

Once cryopreserved, our patients can remain in this state indefinitely. However, the main purpose of biostasis, of course, is not to keep patients preserved forever. The ultimate goal is to one day revive them.

Why revive a person whose condition was, at the time of legal death, incurable? The answer is simple. In the future, diseases that are incurable today will be curable (as we can now deal with diseases that were deadly in the past). Thus, reviving cryopreserved patients in the future will allow us to treat them, saving their lives. Imagine that in several years' time we find a cure for some (if not all) types of cancer. Cryopreserved people suffering from those diseases could be revived and treated with the appropriate technology. They could possibly live longer lives in the future.

hospital cryonics
Successful revival would completely revolutionize the healthcare system


Human cryopreservation is only one part of the process. As with hibernation, if we couldn’t bring people back from this induced comatose state, we wouldn't benefit from this procedure. Similarly, in order to benefit from cryopreservation, we must be able to successfully achieve future revival. At the moment, the necessary technology has not yet been developed. Thanks to the efforts of cryonics institutes, such as Tomorrow Biostasis, there is a chance that we will be able to achieve this goal and completely change medical institutions.

If you are also interested in helping develop this possible life-saving technology, sign up and join our community. Or, to find out more, schedule a call with us.

Tomorrow Bio is the worlds fastest growing human cryopreservation provider. Our all inclusive cryopreservation plans start at just 31€ per month. Learn more here.