Humans go into hibernation, something we only read about in science fiction. is this possible? However, Dr Kevin Fong, who was trained in intensive care medicine, brought us through the mysterious tunnel in the Discovery program he hosted at BBC; ‘Human Hibernation: The Big Sleep’ . In this program, he presented a case happened in 2006 that a Japanese man survived through weeks without food and water in a remote, snowy mountain for 24 days. When he was found, his body temperature was at only 22˚C compared to the normal human temperature of 37˚C, but he was able to make full recovery in the hospital despite experiencing multiple organ failure and blood loss during the fall. His doctor said that he went into a hypothermic state, which was “similar to hibernation”, causing most of his organs to shut down except his brain. It was the first known case of a human went into hibernation for a relatively lengthy time period [1,2].
To further his investigation, Dr Fong went back a century to 1900, to discover a paper published in British Medical Journal claimed that the peasants in the Pskov region in the north-eastern Russia were able to go into the state of deep slumber called “lotska”. The whole family gathered around the stove and quietly go to deep sleep for six months.  An incident that happened more recently in 2012 was reported that freezing temperature and scarce oxygen might have actually saved a man’s life who was trapped inside his car with temperature below 30˚C for two months . A teenage stowaway hid in the wheel wall of an airplane flying five hours from California to Hawaii in 2014. The cold condition with depleted oxygen at high altitudes was believed to put him essentially in a virtual ‘hibernate’ state, or suspended animation.  Another case reported of a toddler whose heart started to beat again after frozen stiff, also had doctors scratching their heads in 2001. She was pronounced clinically dead, when found laid in the snow after wandering in -20˚C winter night with only a nappy on. The frozen conditions that could have killed the toddler were actually responsible for saving her, by putting her body and brain into suspended animation. 
The conditions in these incredible survival stories could have frozen those to death in all accounts but the people involved had actually miraculously survived through the extreme circumstances. Clinically, doctors are already using body-cooling techniques in patients who have serious head injuries. They too also used induced hypothermia to protect the brains of people who have suffered heart attacks to slow down the activity levels of the brains. As far as scientists can tell, we humans do not hibernate naturally, but these extraordinary cases shed light on our understanding of human body is possible to be switched into suspended animation, buying more time for surgeons to save lives under acute situations or trauma injuries, preventing vital organs from irreversible damage.
Hibernation is a seasonal adaptation for some mammals to withstand the cold winters when food is sparse. The metabolic rate and energy consumption of these animals are much reduced when they are hibernating. Fat-tailed dwarf lemurs are the only primates that are able to hibernate, living in the tropical rainforest at Madagascar. In 2004, German physiologists found out the fat-tailed dwarf lemurs are able to hibernate in tree holes even though winter temperatures in its habitat can exceed 30 °C.  “Dwarf lemurs normally have a heart rate of about 100 beats per minute. During hibernation, their heart rate can drop to 3-5 beats per minute and breathing rate is incredibly infrequent and have very low brain activity. The animals truly look like they are died and their body temperature can drop to 5˚C,” said Dr Sheena Faherty, who studied the lemurs’ hibernating behaviour while she was studying in Duke University.  It turned out that they uncovered that the genes drive the physiological change are commonly found in all mammalian species where also have in human genome. It turned out that the genes are not unique to certain animals, so the ability to hibernate on instinct can be turned on and off at different times of the year.
Dr Brian Barnes, Director of the Institute of Arctic Biology at the University of Alaska, has studied the largest hibernating animal, American black bears extensively. They observed how American black bears slow down their metabolism without suffering from muscular loss during hibernation. They believe these bears create artificial load by hijacking the signalling cascades, to fool their tissues to behave as if they were loaded while they are not. Dr Kevin Fong said it is important to understand the complexity of genetics and physiological pathways at the molecular level in these animals, in order to develop drugs that will help to emulate the same response in people. Another finding is from Dr Mervyn Singer, a professor of intensive care and medicine at University College London Hospital. He said the powerhouse of our body cells, mitochondria, seems to be involved in hibernation responses. 
Encouragingly, scientists found that hydrogen sulphide (H2S), a type of simple gaseous molecule that smells like rotten egg, might provide the key to trigger hibernating response. Professor Robert Henning’s team reported that given a high concentration of H2S in hamster cells, seems to protect them from the cold. Works are underway in his lab at the University Medical Centre in Groningen, to study how animals protect their organs by slowing down their body metabolism, as they are entering into a state of torpor and then returning to normal physiology after changes in their environment, or medical intervention. The researchers were also able to identify the required compounds to simulate the production of H2S in rat cells and replicate the resistance to cooling. 
“Such a small and unremarkable molecule, it seems to have profound protective effect on the body challenged by extreme illness or environment. We have stimulated these using human cell culture, and it seems to work equally well as in animal models,” Prof Henning told Dr Fong in the BBC interview, that H2S could potentially cool and preserve living cells without seriously damaging them, and eventually go on to protect non-hibernating animals to survive in low temperatures. The procedure could be made much safer, with slower heartbeats, less bleeding, and less of a dependency on oxygen, by keeping the traumatic patients in a state of hibernation. .
Recent works by Prof. Robert Henning might bring us one step closer to induced hibernation but there are surely plenty questions left unanswered. The body temperature would drop after being subject to such cooling condition, which also causes the metabolism to slow down. However, scientists are still long way off in realising their dreams of ‘human hibernation’ – but evidence presented so far has, undoubtedly, helped us to understanding the mechanism of humans in hibernation.
- Human Hibernation: The Big Sleep. Available at: https://www.bbc.co.uk/programmes/p04vx74h
- The man who ‘hibernated’ for 3 weeks, Available at: https://neurophilosophy.wordpress.com/2006/12/22/the-man-who-hibernated-for-3-weeks/
- Can humans hibernate? As a driver survives for TWO MONTHS trapped without food at -30c, this theory could transform medicine. Available at: https://www.dailymail.co.uk/health/article-2103961/Can-humans-hibernate-As-driver-survives-TWO-MONTHS-trapped-food--30c-theory-transform-medicine.html
- Teen Hitches Ride to Hawaii in Jet’s Landing Gear – And Lives to Tell the Tale. CNN. Available at: https://edition.cnn.com/2014/04/21/us/hawaii-plane-stowaway/
- Newly Discovered Compound Could Unlock the Secrets of Human Hibernation. Available at: https://www.sciencealert.com/newly-discovered-compound-could-unlock-the-secrets-of-human-hibernation