Bear Hibernation
they cause the grave condition called diabetic coma. In small mammals, the build up of ketones is believed to be the trigger for awakening. But bears do not build up significant levels of ketones, despite living purely on their body fat. How they manage this is still something of a mystery, but apparently they recycle ketones into new fat. If humans or other mammals are forced into prolonged inactivity, they lose calcium from their bones and eventually risk osteoporosis. Bears are somehow able to efficiently recycle calcium so that their sturdy bones show not the slightest sign of weakening and their blood calcium levels stay normal. During hibernation, the bear's blood cholesterol level triples, yet they never get gallstones or show signs of vascular disease.
Bears take several weeks to drift into the hibernating state in the fall, generally from October to November. They tend to take a few weeks to come out of it too in the spring from March till May. During this time, their metabolism is slowed and they are in a state called "walking hibernation." They have little appetite and are slow and lethargic. The length of hibernation depends on the severity of the climate, ranging from a couple of months in the South to 6 months or more in Maine or the High Rockies. In really cold areas, the hibernation state tend to be noticeably deeper too. In the warmest areas like Florida, the bears may not hibernate at all.
The potential medical applications are numerous. Bear hibernation studies could yield valuable knowledge for treating obesity, diabetes, cardiovascular disease, osteoporosis, muscle-wasting syndromes, kidney disease and gall bladder problems. Being able to induce a state similar to hibernation with a comparably high rate of protein metabolism would be of enormous value in treating the severely burned or massively injured. Some useful things have already resulted. The special ingredient in a bear's bile, ursodeoxycholic acid, which keeps cholesterol from crystallizing out is already being used to dissolve gallstones in human patients. Studies of the bear's nitrogen recycling system has led to the development of special diets for kidney patients so that they don't have to undergo kidney dialysis nearly so often, or in some cases to avoid it.
Finally, the study of bear hibernation is of real interest to NASA. The loss of muscle strength and bone mass is one of the biggest problems facing humans
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