Hibernating bears protect bones by reducing resorption

July 8, 2015, The Company of Biologists

Even a short period of inactivity can be extremely bad for our bones, and for astronauts facing months in zero gravity, the risks are serious. But there is an animal that has already solved all of the problems faced by immobile humans. Black bears routinely hibernate for 6 months without stirring, and although it can take several weeks for them to regain their full metabolic vigour, their bones seem largely unaffected by the lengthy period of inactivity. Yet, how these impressive beasts protect their bones was a mystery, with previous studies yielding contradictory results.

Intrigued by , Seth Donahue from Colorado State University, USA, and an international team of collaborators decided to monitor the blood levels of specific enzymes and hormones that are known to contribute to bone formation and resorption to find out how bears protect their bones during . They discovered that instead of continually rebuilding the bone, hibernating bears suppress resorption of to maintain their skeleton and the team publishes their discovery in The Journal of Experimental Biology.

The team captured 13 female bears over four hibernation seasons, and collected blood and bone samples from the animals before releasing them back into the wild the following spring. Carefully analysing the blood samples for bone-specific alkaline phosphatase (BSALP) and tartrate-resistant acid phosphatase (TRACP) - which indicate bone rebuilding - the team found that the blood enzyme levels fell in the hibernating bears, suggesting that the hibernating animals were suppressing bone remodelling. And when the team analysed the levels of bone-regenerating osteoblast cells at the surface of the bone, they plummeted from 2% before hibernation to 0.15% during hibernation. However, the levels of cocaine and amphetamine regulated transcript (CART) - which is known to reduce - increased 15-fold during hibernation. So, instead of constantly rebuilding, the bears were protecting their bones by suppressing resorption of the tissue. The team also found that the bears' blood calcium levels varied little from season to season, suggesting that the animals balance resorption and formation during hibernation to maintain stable blood calcium levels, which are also essential for healthy organ function and fat and energy metabolism.

'Hibernating are metabolic marvels', say Donahue and his colleagues, adding that these animals appear to be immune to two major epidemics sweeping across the world - obesity and inactivity - suggesting that we could learn a thing or two from these fantastic creatures.

Explore further: Study identifies a hormone that may help hibernating bears avoid bone loss

More information: McGee-Lawrence, M., Buckendahl, P., Carpenter, C., Henriksen, K., Vaughan, M. and Donahue, S. (2015). Suppressed bone remodeling in black bears conserves energy and bone mass during hibernation. J. Exp. Biol. 215, 2067-2074. jeb.biologists.org/lookup/doi/10.1242/jeb.120725

Related Stories

Bears may hold key to osteoporosis treatment

April 6, 2011

All it takes is a few days of bed rest for human bones to start to weaken. Stretch that out many weeks, and we risk full-blown osteoporosis and its attendant woes of broken hips, wrists and vertebrae. Bears hibernate for ...

Recommended for you

Coffee-based colloids for direct solar absorption

March 22, 2019

Solar energy is one of the most promising resources to help reduce fossil fuel consumption and mitigate greenhouse gas emissions to power a sustainable future. Devices presently in use to convert solar energy into thermal ...

EPA adviser is promoting harmful ideas, scientists say

March 22, 2019

The Trump administration's reliance on industry-funded environmental specialists is again coming under fire, this time by researchers who say that Louis Anthony "Tony" Cox Jr., who leads a key Environmental Protection Agency ...

The taming of the light screw

March 22, 2019

DESY and MPSD scientists have created high-order harmonics from solids with controlled polarization states, taking advantage of both crystal symmetry and attosecond electronic dynamics. The newly demonstrated technique might ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.