Could Humans Ever Hibernate?
Could Humans Ever Hibernate?
By Dr. Priyom Bose, Ph.D.
Reviewed by Danielle Ellis, B.Sc.
The marvel and risk of hibernation
Genetic and physiological basis of hibernation
Why don’t humans hibernate?
Implications of human hibernation
References
Further reading
Hibernation is an adaptation found in many creatures that helps them survive
cold and dark winters when resources are unpredictable or insufficient. During
hibernation, many mammals and birds turn down their metabolism to save
energy. The hibernating period varies from one species to another.
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The marvel and risk of hibernation
Certain animals hibernate because of insufficient food supplies during winter.
Therefore, by going into a long, deep sleep, they avoid this harsh period and
wake up when food is more plentiful. Some of the common hibernating animals
are bears, hamsters, little brown bats, eastern chipmunks, and some species of
ground squirrels. Some insects, amphibians, and reptiles also hibernate.
Typically, hibernators consume extra food in the fall in anticipation of their
winter slumber. They store considerable amounts of white and brown body fats
before entering hibernation. Brown fat provides extra body heat and energy
that is needed when the animal wakes up. Interestingly, some animals also
store food in their den for consumption during brief wakeful periods.
Hibernation is generally linked to a significant reduction in core body
temperature and metabolic rate to a fraction of basal metabolic rate (BMR).
Furthermore, the heart and respiration rates decrease dramatically. To date, the
exact physiological definitions of hibernation remain elusive.
Although both hibernation and torpor share many similarities, there are some
dissimilarities as well. For instance, hibernation could last for up to nine
months, whereas torpor lasts for up to less than twenty-four hours. Sometimes,
hibernation can be interrupted, which is known as euthermia, and during this
period, animals heat up and move around for several hours.
The mean metabolic rate of hibernation was estimated to be approximately 6%
of BMR. After entering hibernation, a significant reduction in energy
consumption occurs. For instance, yellow-bellied marmots could save up to 85%
of their energy, which enables their survival during winter months.
Two key risk factors of hibernators are that they are exposed to predators and
unpredictable climates. Furthermore, hibernators could die from lack of fat and
premature awakening.
Genetic and physiological basis of hibernation
Hibernation is controlled by the endocrine system and central nervous system
(CNS). The brain is inherently involved with entrance and awakening from
hibernation. While entering hibernation, activation of hypothalamic regions
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Could Humans Ever Hibernate?
occurs along with inhibition of cortical regions.
A mice model revealed that the introduction of 3-Iodothyronamine (T1AM), an
endogenous thyronamine, binds to trace amine-associated receptor 1 (TAAR1)
and reduces cardiac output and heart rate. Thyroid hormones modulate basal
metabolism at different stages of life. These hormones play a vital role in the
process of hibernation.
Hibernators are resistant to hypoxia and do not undergo organ damage. They
are able to inhibit the apoptotic response in the brain via the regulation of antiapoptotic proteins. In some cases, ascorbate functions as an anti-oxidation
agent that alleviates the increased reactive oxygen species (ROS) levels during
arousal from hibernation. In some hibernators, an increased expression of
glutathione peroxidase-3 gene is observed. This enzyme has been associated
with the detoxification of hydrogen peroxide in plasma.
How does hibernation work? - Sheena Lee Faherty

The hibernating animals also enter an immunosuppressed state to prevent
general inflammation in the body. The reduction in blood leucocytes and
thrombocytes has been correlated with sphingosine-1-phosphate (S1P) levels in
a temperature-dependent manner. During deep hibernation, the body
temperature drops along with the S1P level. In contrast, when a hibernating
creature awakens, the S1P level increases. The clotting factors FVIII and FIX
also reduce significantly during torpor or hibernation, compared to non-
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hibernating species.
Why don’t humans hibernate?
Typically, most animals that hibernate are small, and during cold weather, they
lose the capacity to get adequate food to sustain life. Humans do not hibernate
predominantly because their evolutionary ancestors were tropical animals
without any history of hibernation. In the last hundred thousand years, humans
have only migrated to temperate and sub-arctic latitudes. This time period is
not long enough to evolve all metabolic adaptations required to hibernate.
Importantly, humans discovered fire, shelter, clothes, hunting, and agriculture.
All these factors contribute to human survival in cold weather. Ancient tribes
that tried to sleep through winters were quickly ousted by other tribes with fur
clothes and campfires. Additionally, humans being active year-round, the need
for hibernation did not come up.
Implications of human hibernation
Since genes associated with hibernation are present in the human genomes,
there is a possibility to induce hibernation temporarily using proper molecular
techniques. For instance, genes that are upregulated in hibernation can be
delivered in humans via viral or non-viral vectors to enhance genetic
expression.
Furthermore, small RNA molecules can be delivered to perform gene silencing
and achieve downregulation at the transcriptional level. DNA methylation can be
used to up or downregulate gene expression.
Many chemical compounds, such as Hydrogen Sulphide (H2S), 5′-adenosine
monophosphate, and [D-Ala2, D-Leu5]-enkephalin (DADLE), can induce
hibernation or torpor state in non-hibernating animals. These chemicals
predominantly function as anti-apoptosis, anti-inflammation, anti-oxidation, or
anti-coagulation agents.
If human hibernation were possible, it would be beneficial in certain areas. The
induction of a hypometabolic state would aid in the treatment of critical illness
as it could reduce the risk of organ damage. For instance, induction of
hyperthermia could significantly reduce hypoxia-induced injury that includes
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brain injury and intestinal ischemia-reperfusion (I/R) injury.
Cryonics is an area of research that is perceived to be an unrealistic technique
by most people. This technique is associated with lowering of body temperature
of patients who cannot be saved or cured with current technologies. Cryonics is
linked to preserving a patient via lowering of temperature until the development
of treatments or technologies to revive them and restore their health issues.
Most people perceive cryonics to be an unrealistic approach because induction
of hypothermia in the human body could cause ischemia and reperfusion injury.
Induction of hibernation in astronauts could positively reduce medical
challenges and resource requirements during interstellar space travel. In this
context, NASA induced a mild hypometabolic state in selected individuals, and
this study reported no detrimental effects for up to fourteen days. This
observation indicates the possibility of therapeutic hypothermia in humans.
References
Hunstiger, M. et al. (2023) Non-shivering thermogenesis is differentially
regulated during the hibernation season in Arctic ground squirrels.
Frontiers in Physiology. 14, 1207529. https://doi.org/10.3389/fphys.
2023.1207529
Cottier, C. (2023) Could Humans Ever Hibernate in the Future? [Online]
Available at: https://www.discovermagazine.com/the-sciences/couldhumans-ever-hibernate-in-the-future
Couzens, D. (2022) What is hibernation, how does it work, and which
animals do it? [Online] Available at: https://www.discoverwildlife.c
om/animal-facts/what-is-hibernation
Constant, T. et al. (2020) Integrating Mortality Risk and the Adaptiveness
of Hibernation. Frontiers in Physiology. 11(706). https://doi.org/10.3
389/fphys.2020.00706
Vaughan, D. (2019) Why Do Some Animals Hibernate?. Encyclopedia
Britannica. [Online] Available at: https://www.britannica.com/story/whydo-some-animals-hibernate
Pan, M. (2018) Hibernation induction in non-hibernating species.
Bioscience Horizons: The International Journal of Student Research. 11.
https://doi.org/10.1093/biohorizons/hzy002
Lewy, A. J. et al. (2009) Winter Depression: Integrating mood, circadian
rhythms, and the sleep/wake and light/dark cycles into a bio-psychoSaved from URL: https://www.news-medical.net/health/Could-Humans-Ever-Hibernate.aspx
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social-environmental model. Sleep Medicine Clinics. 4(2), pp. 285–299.
https://doi.org/10.1016/j.jsmc.2009.02.003
Lee, C.C. (2008) Is human hibernation possible? Annual Review of
Medicine. 59, pp.177-86. doi: 10.1146/annurev.med.59.061506.110403.
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Last Updated: Nov 22, 2023
Written by
Dr. Priyom Bose
Priyom holds a Ph.D. in Plant Biology and Biotechnology from the University of
Madras, India. She is an active researcher and an experienced science writer. Priyom
has also co-authored several original research articles that have been published in
reputed peer-reviewed journals. She is also an avid reader and an amateur
photographer.
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