It might seem that hibernating bears only serve as inspiration to sluggards and couch potatoes. But it turns out that astronauts, and many others, might benefit from emulating some of the ways of the wintering bear.
Hibernation is an astounding, if lethargic, physical accomplishment. “Hibernating bears are metabolic marvels… that have the ability to be physically inactive and obese without experiencing complications such as heart disease, skeletal muscle atrophy and diabetes,” explain Meghan McGee-Lawrence and her colleagues, authors of a recent study in the Journal of Experimental Biology.
During the four to seven cold-weather months of hibernation, bears don’t eat or drink. They may rarely urinate and defecate, or they may not at all. Their body temperature decreases by roughly 10˚ F, and they may take fewer than two breaths per minute. By the time they emerge in spring, they’ve lost one fourth of their body mass—but not from their bones, which remain as strong as ever.
Astronauts may be immediate beneficiaries of the research, since extended periods of time in microgravity can lead to losses in bone density. Here’s Phillip Oldfield, reporting for The Guardian:
One of the major side-effects of prolonged weightlessness is spaceflight osteopenia, a condition where reduced stress on the bones triggers bone loss. Astronauts on the Mir space station, for example, lost on average 1-2% of their bone mass each month. The condition can be a limiting factor for the length of missions that astronauts can endure.
Our bones are constantly being torn down and rebuilt. If you don’t put stress on them by pushing against gravity—either because you’re not moving, or because you’re in space—the rebuilding phase of this “remodeling” doesn’t keep pace.
In the new study, researchers measured a number of markers in the blood of hibernating bears, concluding that bears maintain their bone strength by slowing down the remodeling altogether.
McGee-Lawrence and her colleagues inferred this from measurements of three molecules in the bears’ blood. The first is a small protein called “cocaine and amphetamine regulated transcript” (CART). One of this protein’s (non-stimulant-related) functions is putting the brakes on the biological machinery that excavates calcium from bones and dumps it into the bloodstream. The authors found that CART increased by a factor of 15 in hibernating bears. Two other chemicals called BSALP and TRACP, which contribute to bone rebuilding, barely increased—indicating that both the tear-down and rebuilding processes had slowed down.
The results help shed light on how your body manages the complex process of creating and destroying your skeleton. This understanding will not only help researchers figure out ways for astronauts to travel to Mars safely, but also may help treat diseases like osteoporosis, which affects approximately half of women over age 50.
Photo credit: Tambako The Jaguar/Flickr (CC BY-SA)