Hibernating Bears Hold Lessons for Human Health

Jan. 14, 2004 — -- The black bear may be unique in the animal world with it's extraordinary ability to emerge from months of hibernation with bones that are about as strong as when it went into its den for the long winter. A shorter period of bed confinement leaves humans with bones so weak they can snap like a dry potato chip, and an aging population has left millions of Americans suffering from osteoporosis.

How bears manage to avoid both those maladies is unknown, but Seth Donahue is determined to find out.

Donahue is an assistant professor of biomedical engineering at Michigan Technological University, and if he can figure out just what makes black bears so different he may be able to create a drug that will help people with osteoporosis. Half the women and a fourth of the men who are over 50 will suffer a bone fracture related to osteoporosis this year, according to the Osteoporosis Foundation.

Donahue and his fellow researchers have found that the bones of a black bear get stronger as it gets older, while ours get weaker. And a black bear is somehow able to recycle calcium and restore its bones, even while fasting and sleeping.

Those major differences between humans and Ursus amaricanus makes it worthwhile to mess around with black bears, a greatly misunderstood animal that tends to be as fearful of humans as humans are of it. Yet they can be extremely dangerous, and although called "black bears," their color can range from light gray (also known as glacier bears) to cinnamon to dark brown. Occasionally they are as white as a polar bear, although much smaller.

Donahue says he and his colleagues still have a long way to go before they can figure out exactly how the bears cope with long periods of inactivity, but he has a theory and some evidence to suggest that he's on the right course.

"Bone loss is related to keeping blood levels of calcium at certain levels," Donahue says. Bears apparently have some "unique features" that allow them to keep calcium near the right level. Whereas other hibernators lose calcium through urinating and defecating, bears do neither during hibernation and apparently are able to recycle calcium that is released into the blood stream during bone deterioration.