QuestionCan humans hibernate?
Hopes&Fears answers questions with the help of people who know what they’re talking about. Today, we ask scientists and researchers to find out whether humans can enter a state of suspended animation.
Come the bleak days of winter, when the sun barely rises, the trees are bare and the cold cuts through your Heattech, most of us wish we had the ability to store our resources and energy, and just hibernate the season away. But is it such a stretch to think that, well, humans could do it eventually? If not through all of February, at least for a few moments when it might really matter (like in the case of a medical emergency, or long-distance space travel).
We asked scientists and researchers to help us understand: is it biologically possible for humans to enter a state of susended animation? And if and when we are able to, what is it good for?
Sheena L. Faherty
Researcher in the biology and genetics of hibernation, Ph.D. candidate, Duke University
The short answer? In theory, yes.
The long answer? It's complicated. Let me explain. Scientists, like myself, who study this amazing physiological feat have reached the same conclusion: That is, all hibernating mammals use the same genetic architecture to hibernate. Hibernation happens from genes being turned on and off—much like a light switch—in very unique patterns throughout the year to modulate physiology. And, importantly, these genes are shared among the entire mammal family tree. They are not genes that evolved specifically for hibernation. Therefore, it seems as though all mammals—including humans—might actually have the genetic capacity for hibernation. It's literally written in our DNA.
There have been a singular examples in the media that suggest that this theory might hold water, including documented cases of people entering into something that looks intriguingly like hibernation. For example, back in April 2014, a young man stowed away in the wheel well of an airplane from California to Hawaii. At that altitude (and those bone-chilling temperatures and low oxygen levels) he should have died (and won the Darwin award posthumously). But, he didn't. He walked away from that very lucky incident just fine and dandy. Was it human hibernation? It's a very compelling notion and seemingly quite feasible once you boil it down to the As, Ts, Cs, and Gs that make up our genetic code.
However, here's where it gets messy. We still don't really understand the unique combinations of expressed genes that make hibernation happen, nor do we even know where to begin in terms of expressing those patterns in humans. What sorts of outside forces are needed to get the correct pattern to make hibernation happen?
The whole issue is convoluted by how our environment affects genes that are being expressed. Animals that hibernate are at the mercy of their environment, using hibernation to avoid periods of cold weather or resource scarcity, when other behaviors like migrating to warmer environments or staying active during the winter might be more energetically costly for them. Humans have used our massive brains to figure out how to manipulate our environments. We build shelters, we use various means to provide warmth, and we have grocery stores that cater to our every need even in winter. So, our environments would never prime our genome to respond to the winter months in such a way, even despite having the capability to do so.
But—and this is a big "but"—if we figured out how to induce hibernation in humans, using this shared genetic architecture, it literally would be the "coolest" thing to ever happen to mankind. Hibernation has many important biomedical applications. For example, if a soldier is wounded on a battlefield and needs emergency medicine, inducing hibernation for the short-term would be beneficial for transportation to a medic. Same goes for patients waiting for organ transplants. Understanding how hibernating animals regulate metabolism throughout the year, avoid atrophied muscles from up to eight months of disuse, survive lack of circulation to peripheral tissues, and other similar issues, these are very intriguing lines of investigation. And finally, my favorite, being a total sci-fi nerd: human hibernation would be extremely useful for long-distance space travel!
Bear hibernation by the numbers
The highest number of months bears have been known to hibernate
The number of pounds a bear can gain per week in preparation for hibernation
The body temperature bears maintain during hibernation
The number of beats per minute bears average in the fall at the start of hibernation
The numer of beats per minute bears average in the winter at the height of hibernation
The number of calories a day supplied on average by the break down of fat tissue in bears during hibernation
Stam M. Zervanos, Ph.D.
Professor Emeritus of Biology, Penn State University/Berks
Some day, in the near future, we will unlock the mechanism of mammalian hibernation and apply it to humans; mostly for medical purposes. Humans possess similar metabolic processes to mammalian hibernators. Most likely, the form of hibernation will be similar to that of bears, where the metabolism slows down with a corresponding decrease in heart rate and body temperature. This would be very important during some complicated surgeries and trauma cases.
In mammals, "hibernation" is a state of suspended animation, with profound reductions in metabolism, oxygen consumption and heart rate. "Suspended animation" refers to the slowing or stopping of life processes by exogenous or endogenous means but without termination.
Hannah Carey, Ph.D.
Professor, School of Veterinary Medicine at the University of Wisconsin-Madison
Currently, humans do not have the ability to hibernate. Hibernation is defined as seasonal periods (typically winter) when an animal undergoes bouts of "torpor"—that is, periods of depressed metabolism when physiological parameters like body temperature, heart rate, and breathing fall below "normal" values. Torpor enables organisms to conserve energy when food is less available and air temperatures are low, making it more costly to maintain normal metabolism and high body temperature. We have evolved such that survival during challenging environmental conditions like winter is achieved without having to resort to entering torpor states for energy conservation.
But there are good reasons why humans might want to enter into states of torpor, or even full hibernation. The major one is for medical reasons. In conditions like shock, massive blood loss, cardiac arrest, and certain types of surgical procedures, the ability to slow down metabolism and lower body temperature may extend survival time for patients and prevent life-threatening side effects like ischemic damage and inflammation.
Use of torpor and hibernation in humans may also aid our ability to travel to distant regions of space by reducing the need to pack enough food for journeys that take months—or years—to complete, and to minimize dangers like radiation damage to the body.
Right now, we don't have the ability to easily enter torpor states on our own, and physicians do not yet have the tools to induce torpor and hibernation safely and reversibly for medical uses—mainly because scientists do not yet have a full understanding of how hibernation and torpor happens in nature. But scientists are making good progress along these lines, and on inducing torpor states in species that do not hibernate (such as lab rats), making it more likely that we may achieve this for humans in the future.
We even have evidence from humans themselves that torpor-like states are possible; for example, some yogis are able to lower their heart rate and metabolism during deep meditative states, and some people who are accidentally trapped in extremely cold water with no measurable heartbeat or brain activity for long periods have been revived. We also know that some non-human primate species, specifically, lemurs regularly use torpor and hibernation as part of their lifestyles. All of this means there is good reason to believe that we already have the genetic capacity and physiological "machinery" within us to induce torpor and hibernation—we just need to know how to activate the right pathways within our bodies, and make it so!
In 2006, a Japanese hiker named Mitsutaka Uchikoshi survived 24 days in the cold with no food or water in a state akin to hibernation. He had nearly no pulse, organs that had stopped functioning and a body temperature of 72 degrees. Hirohito Shiomi, a professor at Fukyama University told the Associated Press: “This case is revolutionary if the patient truly survived at such a low body temperature over such a long period of time. Researchers would have to clarify whether Uchikoshi's body temperature dropped very quickly, or whether he started losing body heat much later and was in fact dying when rescuers found him."
Kenneth Storey, Ph.D.
Canadian Research Chair in Molecular Physiology, Professor, Carleton University
Currently humans cannot hibernate and cannot be induced to hibernate. However, several species of lemurs—which are primates, just like humans are— can hibernate and live in "suspended animation." There is active research in our lab to learn the molecular mechanisms as to how this is done.