Hibernating Bears Hold Lessons for Human Health

They anesthesize the bears before sucking out some of their blood.

"Obviously, you don't want the bear to wake up," says Donahue.

One major difference between humans and bears emerged quickly in the research. Animal bones are "continuously remodeled," Donahue says. Bone tissue is broken down by "resorption cells," he adds, and new bone is formed by "forming cells."

"During disuse, like when humans are confined to bed rest for medical reasons, or even in other hibernators like bats and ground squirrels, the bone resorption increases so more bone is being removed and bone formation decreases, so less bone is being made.

"That's normal in all mammals except for the black bear, which only increases the resorption. It doesn't decrease the formation. It continues to form new bone."

To do that they have to have a continuous supply of calcium, but they don't eat or drink while in hibernation, so the calcium is recycled. What's taken from the bone is put back in.

But how do they do that?

Donahue suspects it's all in the hormones.

More Mystery

One hormone, especially, is suspect. The parathyroid gland secretes a hormone called parathormone which is the subject of much research today. In various clinical trials the human version of that hormone is being given to patients with osteoporosis, and it appears to be helping, Donahue says.

But when he and his colleagues tried to determine the precise structure of that hormone in the blood taken from the bears, they were in for a surprise. The standard test, which is based on the human hormone, didn't work. Neither did the ones for rats and mice.

The bear hormone was clearly different. And therein could lie a valuable bit of information.

The researchers have begun the time consuming process of breaking down the bear hormone into various parts to see if they can determine what makes it different. If they can, they might be able to produce a synthetic version of the hormone and see if it helps humans with osteoporosis.

That would be a major achievement in itself, but it doesn't completely explain how bears work their magic.

Most animals that hibernate need at least twice the amount of time to recover from hibernation as the amount of time they spend on the couch. But the black bears in the Virginia Tech lab normally hibernate for six months, so they would still be only half way back to normal by the time they are supposed to return to the den. At least, if they were like other hibernators.

Surprisingly, the researchers have found that the black bears ramp up their rate of bone recovery toward the end of their hibernation, and they emerge from the den in nearly as good a shape as when they went in.

And wouldn't it be great if these folks could figure out how bears increase the strength of their bones as they get older? If it's all in the hormones, perhaps there's a pathway here to the elimination of osteoporosis.

But of course, as Donahue emphasizes, we don't really know yet how bears pull off this clever bit of physiology. So we don't know if their hormones will help us keep our bones strong.

Maybe they'll just make us grow black hair all over our bodies, and tend to walk on all fours.

Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.

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