How Hibernating Bears Beat Bone Loss

Their bones grow even when they are lying dormant.

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Black bear crossing the road in Glacier National Park.

The science of hibernation, which I've written about here and here, has fascinated me for some time. How do animals go dormant—hibernation is actually not a form of sleep—for months at a time and not waste away in the process?

If I had to perform virtually no bodily functions for the entire winter, I would die of thirst, or starve, or burst my bladder long before spring arrived. Even if I could put my basic metabolic needs aside for the season, my muscles and bones would dissipate from disuse. Come March, I'd be too weak to get up, never mind see my shadow.

Hibernating animals, however, tap into some impressive physiological abilities that humans have long since lost. Scientists and medical researchers are trying to figure out how animals do it. They hypothesize that if we humans could revive our capacity to hibernate, perhaps with the aid of pharmaceutical treatments, we could improve our odds of surviving heart attacks and strokes, car accidents and war wounds, and other sorts of threats to life and limb.

An interesting story in yesterday's Wall Street Journal reminded me how much I still don't know about this field of science. The writer, Ivan Oransky, described how researcher Seth Donahue determined that bears make a special hormone that helps them build new bone material during hibernation. The new bone replaces material that they are losing. Striking a balance between bone generation and bone loss is what enables us generally to maintain bone strength, even though the actual molecules in our skeletons are continually coming and going. Donahue's research could help combat osteoporosis, which is what occurs when bone loss outpaces bone generation—and is also what would happen to me if I attempted to hibernate without having that bear hormone.

The story notes that bears have to be anesthetized before blood samples can be drawn from them. "But how do you get a hormone sample from a bear...? Very carefully," Oransky writes. Otherwise, a bear "might awaken, distorting the results and putting the researchers at risk."

That brought to my mind a memorable lecture that I heard a couple of years ago at a scientific conference in Virginia Beach, Va. Hank Harlow, a professor of zoology and physiology at the University of Wyoming in Laramie, spoke about how bears manage to survive hibernation. Like Donahue, Harlow took care when harvesting tissue samples from hibernating bears. One misstep, he said, and the bear could rouse itself with startling speed, roaring out of the den in hot pursuit of any researcher quick-footed enough to flee. That bears can "wake up" so fast from hibernation is a physiological feat in its own right—months of immobility would cause a person's muscles to atrophy to the point that he or she couldn't get up unassisted. That's why Harlow said scientific study of bears could aid another type of patient: people who are bedridden for months at a stretch.