Hibernation is a complex solution to a simple problem. In winter, food is scarce. To survive this seasonal famine, animals, such as the arctic ground squirrel and black bear, induce a sedentary state under which physiological shifts keep them alive despite the lack of food, water and movement. Researchers and doctors alike are interested in how these hibernation tricks could help humans with their own health.
THREAT: Stroke
INSIGHT: Blood flow in the brain of a hibernating arctic ground squirrel drops to a tenth of normal. Typically such oxygen deprivation would cause a stroke. But these squirrels can survive all winter because their metabolism lowers to 2 percent of its summer rate—requiring much less oxygen to maintain. If paramedics could similarly lower the metabolism of a human patient immediately after a stroke—perhaps by cooling the body—they might prevent permanent brain damage, says Brian Barnes, a biologist at the University of Alaska Fairbanks.
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THREAT: Diabetes
INSIGHT: People who gain a lot of weight often stop responding to insulin. The hormone regulates the amount of glucose that cells take up from the blood; too much sugar in the blood results in type 2 diabetes. Yet grizzly bears gain 100 pounds or more each autumn and somehow avoid diabetes. A recent study found that the grizzlies' fat cells become more sensitive to insulin as they prepare for the winter, allowing the bears to keep processing and storing sugar. Scientists at biotechnology company Amgen are now testing whether tweaking the same protein that controls sensitivity in diabetic humans could have similar results.
THREAT: Osteoporosis
INSIGHT: If a human were to lie still for long periods without food, his or her bones would slowly degrade. A black bear, however, emerges from its den after winter just as strong as ever because its bone is recycled at 25 percent of normal levels during hibernation. Researchers at Colorado State University are now trying to identify the hormones that control this extreme limit on bone turnover. They aim to create a drug for people at risk for osteoporosis that similarly protects bone density.
THREAT: Heart Disease
INSIGHT: During cardiac surgery, a patient becomes oxygen-deprived when the heart stops beating. To cope, the body switches from aerobic to anaerobic metabolism. Unfortunately, the change creates lactic acid, which can kill cells if it builds up. Damage of this kind does not occur in hibernating arctic ground squirrels, likely because they break down more fats than sugars even after the heart has slowed to just one beat per minute. Collaborating researchers at Duke University and the University of Alaska Fairbanks are now working to identify how this species prioritizes fat as fuel in low-oxygen conditions. Finding a way to coax cardiac surgery patients to do the same may reduce injury to organs during procedures.