Bears Give Clues to Avoiding Osteoporosis

Even though they hibernate during winter, their bone strength stays constant

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TUESDAY, Dec. 23, 2003 (HealthDayNews) -- Sleeping bears don't take osteoporosis lying down.

Inactivity is a prime cause of osteoporosis in most animals, including humans. Black bears hibernate for as long as six months a year. Despite that extended period of idleness, the bruins manage to avoid becoming afflicted with osteoporosis.

Finding out how they do it may offer clues about how to prevent osteoporosis in humans.

In an effort to learn more, Michigan Technological University researchers took a series of blood samples from five black bears. The blood samples, taken throughout the bears' annual cycle, were monitored for metabolic markers of bone metabolism.

The blood samples revealed that, while bone breakdown in the bears does increase during hibernation, bone production remains constant and may even peak as the bears emerge from hibernation.

Bears don't eat during hibernation, so food isn't available as a source of calcium to rebuild their bones. Bears also don't urinate or defecate while they hibernate. That means the calcium already in their bodies remains there as they doze away the winter. So they recycle the existing calcium in their bodies maintain their bones.

The researchers also say that age, another risk factor for osteoporosis, doesn't seem to have an impact on bears' bones either. They tested the strength, porosity and mineral content of bear bones and found strength and mineral content increases significantly as bears age, while porosity remains constant.

The study appears in the current issue of the Journal of Experimental Biology.

The researchers plan to compare structural differences between human and bear versions of two hormones that regulate bone metabolism.

More information

Here's where you can learn more about osteoporosis.

SOURCE: Michigan Technological University, news release, December 2003

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