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Hibernators Might Improve Human Health

     Here we are in mid-winter. If you live in one of the colder, snowier parts of the country you're beginning to feel the toll of the shorter days and cold temperatures. Wouldn't it be nice to just eat a big meal, hop under the covers and hibernate until May? Even if this were physically possible, there would be many adverse physiological affects to being sedentary for 4 months. Why is it then, that other mammals can do it? How can learning about hibernators help us understand human health? Scientists have been researching the effects of hibernation on other mammals and their bodies abilities to combat the negative consequences of hibernation. They hope to not only learn more about these animals, but also to learn more about human health. Studying bears and other hibernators might unlock clues to combating human conditions like diabetes, osteoporosis, stroke and heart disease.
Grizzly Bear (photo: Jacob Bøtter)
     Hibernation is not simply sleep. After a lot of preparation, the body's heartbeat, breathing and metabolism slows down incredibly. Black bears are inactive for about 6 months of the year. Despite this inactivity they are able to maintain a healthy bone density and emerge in the spring without the type of bone loss that a human would face after being sedentary for so long. Over a human lifespan we lose more bone than we can replace, leading to weaker bone structure. Bears are able to "recycle" bone throughout their hibernation. Scientists from Michigan Technological University and Colorado State University have been studying which hormones regulate the blood calcium in these bears. Researcher Seth Donahue found that parathyroid hormone (PTH), a hormone found in both the bears and humans, has a unique amino acid sequence in the black bears. Mice injected with the bear PTH have developed stronger bones, indicating that perhaps this hormone could also help humans with bone diseases such as osteoporosis. 
     Diabetes and obesity are becoming a rampant problem in the United States. Grizzly bears may help us to understand how to treat diabetes more effectively. As humans gain weight their bodies stop responding to insulin, a hormone that is key in metabolizing sugars and fats properly. When the body no longer responds to this hormone, the person becomes diabetic. Grizzly bears must gain a lot of weight before they go into hibernation. As they gain more fat they actually become more sensitive to insulin, the opposite to what occurs in humans. The bears are able to switch their metabolism back and forth depending on their needs throughout the year. Researchers at the Washington State University Bear Center and the drug company Amgen are looking at the protein responsible for the bear's ability to change its insulin regulation with the seasons. This protein, PTEN, controls for insulin sensitivity and resistance. If we understand more about this protein then we might be able to use this information to help treat the negative effects of diabetes while patients manage weight and other health risks. 


      Another hibernator, the arctic ground squirrel, might be able to help us prevent strokes and heart disease in humans. Brian Barnes studies this phenomena at the University of Alaska Fairbanks.  During a stroke, there is a lack of oxygen flowing to the brain. A hibernating ground squirrel has a brain blood flow that is a tenth of the normal amount. We would expect that this would cause a stroke in the squirrel. However, the ground squirrel also has a much lower metabolism when it is hibernating than it does when it is active. Using this idea, it is thought that if we could lower the metabolism of human stroke victims shortly after their stroke then it might prevent brain damage. Arctic ground squirrels also may be key in learning about preventing heart disease. When the human heart stops it cannot pump oxygenated blood around the body properly, which changes metabolism and causes lactic acid builds up, killing cells. The squirrel does not have this problem. Even when their hibernating heart has slowed to one beat per minute, the squirrel is able to break down more fats than sugars. Understanding how this animal can make the switch to using fat to fuel metabolism could help prevent damage to human organs of heart surgery patients.
      We might not be able to sleep away a cold, snowy day, but perhaps the adaptations of hibernating animals can help us find ways to improve our health. It seems like Mother Nature is always there to back us up, we just have to unravel her mysteries first!

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Hibernation and Health Resources:
A few good books about bears and hibernation, click the image for more information.

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