Humans Hibernate

Humans Don’t Hibernate, but We Still Need More Winter Sleep

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Summary: REM sleep is 30 minutes longer in Winter than in Summer for most people, a new study reveals.

Source: Frontiers

Whether we’re night owls or morning larks, our body clocks are set by the sun.

Theoretically, changing day length and light exposure over the course of the year could affect the duration and quality of our sleep. But figuring out how this applies in practice is difficult. Although studies where people assess their own sleep have suggested an increase in sleep duration during winter, objective measures are needed to determine how exactly the seasons affect sleep.

Scientists studying sleep difficulties have now published data in Frontiers in Neuroscience that shows that, even in an urban population experiencing disrupted sleep, humans experience longer REM sleep in winter than summer and less deep sleep in autumn.

“Possibly one of the most precious achievements in human evolution is an almost invisibility of seasonality on the behavioral level,” said Dr Dieter Kunz, corresponding author of the study, based at the Clinic of Sleep & Chronomedicine at the St Hedwig Hospital, Berlin.

“In our study we show that human sleep architecture varies substantially across seasons in an adult population living in an urban environment.”

Studying sleep

A team of scientists led by Ms Aileen Seidler in Dr Kunz’s working group at the Charité Medical University of Berlin recruited 292 patients that had undergone sleep studies called polysomnographies at the St Hedwig Hospital.

These studies are regularly carried out on patients who experience sleep-related difficulties, using a special laboratory where patients are asked to sleep naturally without an alarm clock, and the quality and type of sleep can be monitored as well as the length of sleep.

Although the sleep disorders could potentially affect the results, this makes for a large study group evenly spread throughout the year, allowing for the investigation of month-to-month differences.

The team excluded patients who were taking medications known to affect sleep, technical failures during the polysomnography, and REM sleep latency longer than 120 minutes, which suggested that the first REM sleep episode had been skipped. Once these exclusions had been made, 188 patients remained. Most of their diagnoses showed no seasonal pattern, but insomnia was more commonly diagnosed towards the end of the year.

Winter sees more REM sleep

Even though the patients were based in an urban environment with low natural light exposure and high light pollution, which should affect any seasonality regulated by light, the scientists found subtle but striking changes across the seasons. Although total sleep time appeared to be about an hour longer in the winter than the summer, this result was not statistically significant.

However, REM sleep was 30 minutes longer in the winter than in summer. REM sleep is known to be directly linked to the circadian clock, which is affected by changing light. Although the team acknowledged that these results would need to be validated in a population which experiences no sleep difficulties, the seasonal changes may be even greater in a healthy population.

This shows a woman sleeping
Although total sleep time appeared to be about an hour longer in the winter than the summer, this result was not statistically significant.

“This study needs to be replicated in a large cohort of healthy subjects,” cautioned Kunz.

Although most people’s waking time is currently largely out of their control, due to school or work schedules, society might benefit from accommodations which would allow humans to respond more effectively to the changing seasons. In the meantime, going to sleep earlier in the winter might help accommodate human seasonality.

“Seasonality is ubiquitous in any living being on this planet,” said Kunz.

“Even though we still perform unchanged, over the winter human physiology is down-regulated, with a sensation of ‘running-on-empty’ in February or March. In general, societies need to adjust sleep habits including length and timing to season, or adjust school and working schedules to seasonal sleep needs.”

Can Humans Hibernate? Idea May Not Be So Crazy

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Occasionally, seemingly miraculous cases of humans going in and out of hibernation-like states are reported. In 2006, for example, a 35-year-old man was rescued on a snowy mountainside in Japan 24 days after going missing. He seemed to have survived by entering a state of nearly suspended animation: His organs had shut down, his body temperature had dropped to 71 degrees, and his metabolism had slowed almost to a standstill. Subsequently, the man made a full recovery.
How could this extraordinary event have occurred? Was the Japanese man really hibernating like a bear? And is the ability to enter and wake from a prolonged slumber restricted to a few lucky individuals, or, in the right circumstances, can we all do it?

In recent years, many scientists have come to believe that outlandish survival stories are not mere flukes or media exaggerations, but rather manifestations of a latent ability to hibernate that all humans possess.
Hydrogen sulfide: The sleeping gas
A cell biologist named Mark Roth and his colleagues at the Fred Hutchinson Cancer Research Center in Seattle think that a gaseous compound called hydrogen sulfide may be the key to suspended animation.
In a watershed experiment in 2005, the researchers induced hibernation for the first time in lab mice by having them inhale large doses of hydrogen sulfide gas. The chemical bound with cells in place of oxygen, effectively shutting off all metabolic processes in the mice, and significantly reducing their body temperature. Hours later, when scientists replaced the hydrogen sulfide with normal air, the mice came out of hibernation and showed no adverse effects from the ordeal.
“We think this may be a latent ability that all mammals have potentially even humans and we’re just harnessing it and turning it on and off, inducing a state of hibernation on demand,” Roth told LiveScience, a sister site to Life’s Little Mysteries, shortly after the publication of his and his colleagues’ results in the journal Science.
Since then, researchers in the Roth Lab have continued experimenting with the compound. They are studying its effect on C. elegans, a species of roundworm. “Worms have exactly the same response as humans to hydrogen sulfide,” Jason Pitt, a postdoctoral fellow in the Roth Lab, recently told Life’s Little Mysteries. “If you get exposed to hydrogen sulfide, you have what’s called a ‘knockdown.’ You immediately lose consciousness. If you stay there, you’ll die. If you’re removed and taken into fresh air, you recover. These small worms do the same thing.”
Because humans and worms respond similarly to hydrogen sulfide exposure, and because C. elegans is genetically simple, making its reaction to the compound easier to decipher than ours, it is a perfect model organism for studying the chemical’s intriguing effects.
Someday, researchers hope the gas can be used to induce hibernation in humans, which could enable everything from long-distance space travel to suspended animation during trauma recovery. Need to get to Jupiter, but can’t fit enough food on your spaceship? Just hibernate on the way. Need a kidney transplant, but don’t have an organ donor lined up? Just go to sleep and wait for one.
But we’re not at that point yet. “Because we don’t know more about how hydrogen sulfide is working, we haven’t been able to do the same thing in people as we’ve done in other organisms,” Pitt said. “We’re starting to learn more about how this agent does what it does. By studying different related molecules and how they work, we’re starting to tease out what’s going on.”
Even if gas exposure can eventually be used to induce suspended animation in humans, how does that explain fluke cases of humans entering hibernation by themselves?
“Since our lab’s initial work, a lot of people have shown that there is hydrogen sulfide endogenously in our bodies,” Pitt said. “There’s growing evidence that it is this sort of internal regulatory molecule that’s present in all of us. But we don’t yet understand what it’s doing or how it works.”
Though they don’t claim to know everything about it, the scientists do think the compound has been in us since life began, 3.5 billion years ago.
We’re a lot like bacteria
“It makes a lot of sense that humans and other mammals would have a latent ability to enter suspended animation,” Pitt said. “Early in the history of the Earth we had no oxygen. However, you did have these sulfur compounds like hydrogen sulfide.”
“There are organisms out there today in extreme environments that respirate with hydrogen sulfide,” he continued. “Presumably we all came from those environments. Because biology carries its baggage around with it, it would not be surprising if humans had an ability to do some pretty ancient chemical reactions. We’re talking about things that happened 3.5 billion years ago when oxygen first started to appear and when cyanobacteria started changing the Earth’s chemistry.”
Many types of bacteria are able to turn their metabolism on and off as a survival mechanism. According to Pitt, we shouldn’t be much different.
“Our eukaryotic cells are symbiotic organisms, he said. “Our mitochondria evolved from a bacterium. Basically we’re a lot more like bacteria than we like to think.”