When bears go to sleep for months at a time, their heart rate, metabolism, and body temperature drop to almost nothing. Despite this, their bodies apparently go into overdrive in other areas, healing wounds so that they're good as new.
This really should be impossible, considering most mammals pretty much lose the ability to heal wound effectively the moment their body temperatures start to drop. And yet somehow American black bears use hibernation as the time to heal all wounds, unleashing a supercharged immune response that erases all hints of infection and injuries. In their new paper, researchers from the Universities of Wyoming and Minnesota explain how they made this remarkable discovery:
"We identified a few animals each year with injuries resulting from gunshots or arrows from hunters; bite marks from other bears or predators. These wounds were considered to have been incurred some time before the bears denned, and were often infected or inflamed...in early winter. Yet typically, when we revisited bears in their dens a few months later, most wounds had completely resolved whether or not we [cleaned them], sutured the areas or administered antibiotics."
The researchers were then able to confirm these results experimentally by tracking cuts on a small group of bears over a few months. The bears all entered hibernation with the wounds still in evidence, but by the time they awoke the wounds were gone, there was no sign of infection, and generally there was only the slightest wisp of scar tissue, if anything. Otherwise, it was as though the cuts had never happened - even hair had started to regrow over the wound. Exactly how bears pull off this healing trick is still an open question, but the researchers hope that their secret might be adapted to help humans better heal from their wounds as well, although hopefully without having to sleep for six months, of course.