Hibernation Could Prolong Life. Is It Worth It?

Hibernation Could Prolong Life. Is It Worth It?

Today’s most elderly bats aren’t supposed to exist. They are categorically tiny mammals. According to the evolutionary rules, their lifespan should be shorter than other small-bodied animals. Many of Earth’s winged mammals defy this trend and live for decades beyond their expiration dates. One species, Brandt’s bat, which weighs just four to nine grams as an adult–all the heft of a quarter–has been recorded surviving to the age of 41 in the wild, almost as long as a standard four-ton Asian elephant, and nearly 10 times as long as its body dimensions might otherwise predict. “That’s just amazingly long-lived for their size,” says Jerry Wilkinson, a biologist at the University of Maryland. “Longer than any other mammal.”

No single factor can explain the astounding longevity of bats. They are clever and collaborative, and their superpowered immune systems help them tolerate viruses that make other animals disastrously sick–traits that undoubtedly help them survive. But one of their anti-aging tricks, among the most biologically elusive in the world, is to simply put off getting older for months out of every year.

As fall dips into winter, the little mammals huddle into caves, trees, and mines, folding up their wings and hanging feet over head. Their body temperature plunges, sometimes approaching freezing; their heart rate slows to a handful of beats per minute; they barely take any breaths at all. “They basically shut down their entire body, drastically reducing all the functions that we typically associate with life,” says Aline Ingelson-Filpula, a biologist at Carleton University. Stretches of hibernation like these have long been understood as almost suspended animation, used to conserve the body’s resources in times of great need. For bats, Wilkinson and his colleagues have found that it may also drastically extend their tenure on Earth.

Time is not what really kills us. It’s the way we use it that makes us sick. For most creatures, the calendar of days and months progresses in lockstep with the internal process of aging. But bats, and likely other hibernators as well, are effectively able to uncouple those clocks, advancing their biological age only when they’re active and awake–even as their chronological timepiece ticks on. “Think of hibernators as just being turned off,” says Hanane Hadj-Moussa, a biologist at the Babraham Institute. “They don’t get as damaged as an organism that has to just deal with life.”

Many scientists think of aging as what happens when the body accumulates life’s wear and tear–the costs of metabolizing food and burning through daily energy demands, the gunky buildup of cellular waste. Hibernation brings those burdensome processes to a near halt. Animals that manage it are “barely doing anything metabolically, and they’re very cold,” says Jenny Tung, a biologist at the Max Planck Institute for Evolutionary Anthropology. This is both caloric restriction combined with cryopreservation. It preserves physiological battery power by slowing down the device, much like turning off the iPhone’s low-power setting.

Scientists were first clued in to the notion that hibernation might be a way to temporarily delay death in the early 1980s, when a team of medical researchers at Harvard found that Turkish hamsters that spent an especially long time in seasonal pseudo-slumber perished later than their peers. In the years that followed, researchers quickly identified several other creatures that belonged to the Wake Less, Live More Club. Among them were ground squirrels, bats, marmots, and lemurs–all of which outlast similar species that don’t hibernate, clear hints that the hibernators were somehow “cheating the game,” says Gabriela Pinho, a biologist at the Ecological Research Institute in Sao Paulo, Brazil.

But it’s difficult to prove that hibernation is an anti-aging strategy. If animals are holed up in dens for months of the year, they’re also usually better hidden from predators and more sheltered from the elements. To confirm that these stints of dormancy were actually, on a molecular level, hitting the “Pause” button on animals’ inevitable march toward death, Tung told me, scientists needed a way to “start asking what’s going on within the cells themselves.”

This year, two groups of researchers, led by Pinho and Wilkinson, respectively, published some of the most convincing data on that front to date, on yellow-bellied marmots and big brown bats. Both studies scoured the genomes of the little mammals, looking for epigenetic modifications–molecular punctuation marks that annotate stretches of DNA, making them more or less easy to read. These marks get shuffled and more scattered as we age, and researchers have studied them closely enough to read their patterns, almost like tree rings, and determine how far our tissues have progressed along the path to old age. Researchers can then determine if a species is molecularly healthy for the number of years it has been alive. This was the case with Wilkinson’s big brown bats.

Pinho, Wilkinson and Adams inspected the bat and marmot genomes during different seasons to see if the animal’s biological age stalled in winter. However, they had accumulated months of chrono time and were quickly reactivated in spring. The differences in DNA modifications were stark enough between the seasons that they were visible “within six months in the same individual,” says Isabel Sullivan, who was part of Wilkinson and Adams’s team.

Hibernation, to be clear, didn’t manifest just to fill nature with geriatric marmots and bats. Its primary purpose is to rescue animals from almost-certain death during resource-poor and often chilly times of year. “It’s a mechanism for survival, just making it to the next stage,” says Liliana Davalos, a biologist at Stony Brook University. It’s possible that this freeze-frame doubled up as a fountain for youth.

Humans have other ways of making it through rough winters–we’ve never needed hibernation to survive. But the prospect of mimicking the act still tugs at our brains. This could allow for quicker emergency surgery. This could allow for far-reaching space travel. It would keep astronauts alive until they reach their destination. Some people will likely queue up if they can enjoy longevity.

Still, “I’d be cautious about saying if we hibernate, we could just double our life span,” Wilkinson said. Plenty of species hibernate and still die at about the age their body size would predict. And as cushy as hibernation might sound, it threatens to exact a tax. While inactive, animals’ brain function fizzles, their weight plummets, and their digestive tract shrivels. Their movement ceases and their reflexes are slow. This makes them vulnerable to predators and increases the chance of them becoming deformed and losing their muscle mass. The immune system’s potency also ramps way down, making bodies super-susceptible to infection. (That’s one huge reason that droves of bats have, in recent years, been felled by white-nose syndrome, a lethal fungal disease that hits hibernators hard.) Creatures that have evolved to hibernate have also cooked up many strategies to counteract its costs, allowing them to bounce back each spring. However, humans haven’t, which means that the human toll will be even greater.

Even the prep for hibernation is arduous. In the fall, pre-hibernation squirrels and bears have to eat themselves into a diabetic coma to stockpile several months’ worth of fat. Yellow-bellied marmots, which can hibernate for up to eight months of the year, have just “four to five months to basically double their weight and reproduce,” Pinho told me, condensing their most important tasks into the brief stretches during which they’re awake. (Their offspring, too, must frantically chow down shortly after they’re born, or risk dying in their first winter underground. )

Hibernation can’t guarantee restful slumber, either. Most mammals must rouse themselves–usually once every couple of weeks or so–to eliminate waste, perhaps sip a bit of water, and, ironically, sleep. These wake-ups are massively expensive: “Every single arousal that a squirrel does takes about 5 percent of the energy that it uses over the entire hibernation season,” Ingelson-Filpula, of Carleton University, told me. The etiquette of torpor is also … different. Some male bats will rouse themselves in the dead of winter to have sex with still-dormant females, which may wake weeks later to find themselves toting around a stranger’s sperm.

And then, there’s the FOMO. Wilkinson explained to me that Hibernation would allow you to “see the world in a future period” and it was a very appealing idea. “But then you lose the opportunity to see things now.” Tung, too, wouldn’t want to forgo any chance “to watch my parents age or my kids grow.” Hibernation might be thought of as getting as close to death as possible without fully succumbing to it. Maybe they’re not living as long if that is the cost bats and marmots have to pay in order to live longer.

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