Do Sleeping Bears Hold Secrets for Human Health?

By now most of Yellowstone’s grizzly bears are snug hibernating in winter dens, safe at last from human dangers.

But in the darkness below the snow, mysteries and miracles unfold, apropos of our Christmas season. Researchers have long known the basics of bear hibernation. These bruins don’t eat or drink or excrete waste for between 150 and 180 days. But when grizzly bears crawl out of their dens in spring, they are specimens of health. They lose very little bone strength or lean muscle mass, though they may lose as much as 30 percent of their fall weight.

Unlike deep hibernators like ground squirrels, bears are not unconscious during their winter slumber, which allows mother grizzlies to give birth in the dead of winter to a cub or two, each the size of a teacup, which she groggily nurses in her den until sometime during April or even May.

How does a mother bear pull off this feat? Part of her secret involves obesity. Gorging on foods ranging from bison to ants, she packs on several pounds a day during her late summer and fall feeding frenzy.

Her choice of a den site helps boost her chances of successfully reproducing. She digs her den at high elevations and on north-facing slopes where snows pile deep enough to cover the entrance hole and provide not only good insulation but also safety from predators.

What happens next, physiologically, is not only fascinating, but also of potentially profound benefit to us humans — although dependent on the continued ingenuity of medical researchers supported by federal research dollars.

Are scientists getting closer to unveiling the bear’s secrets? Yes and no. They are not yet able to replicate adaptations that might help people suffering from diabetes. Even though “healthy” bears get manifestly obese by the time they den, they do not get Type 2 diabetes. Diabetes occurs when cells are no longer able to take up sugar in response to infusions of insulin. When humans who are starving or who have uncontrolled diabetes rely on fat for energy, the body cannot handle the toxic byproducts of fat catabolism. Not so for bears. They just recycle these byproducts into making more fat.

Researchers are making headway with treatments for osteoporosis. If we are inactive for months, even weeks, our bones deteriorate to the point we can no longer walk. But bears produce a parathyroid hormone that maintains bone density and strength. Today, some doctors are treating people suffering from osteoporosis with a manufactured hormone that matches what bears produce. If that is not a miracle, what is?

Kidney function in bears is also weird and wonderful. If our kidneys did not excrete otherwise toxic wastes such as uric acid, we would soon die. But get this: in winter, microbes in bears’ guts convert urea to nitrogen to make new amino acids that are the building blocks of protein. This enables bears to maintain lean body tissue in the comfort of their own dens without eating or eliminating waste.

Scientists studying hibernation are not the only ones who at some point just stand back in awe.

Indeed, awe lies at the heart of the relationship between ancient cultures and bears. All species of bear share the ability to seemingly die in winter and re-emerge in spring with new life. Because of this, bears have symbolized transformation since time immemorial.

In modern ecology, you hear that the grizzly bear is an “umbrella species.” The health of grizzly bear populations engenders health for entire ecosystems. Ancients had a different way of orienting to the same issue. There is an old story of a bear that goes into her den to dream the world into being each winter. In her imagination, she creates each plant and animal — entire ecosystems — during the long barren months.

But I have found one story that truly baffles me, a contemporary story. It legitimizes killing bears for ego gratification and extols destroying bears that cause any problems for people. This story is the opposite of reverence and wonder.

The ethos of domination and violence that drove the genocides of bears, bison, wolves, and native peoples survives today in many forms, especially in the West, and especially in our institutions of wildlife management. But people and institutions are changing. Thankfully, reverence, tolerance, and gratitude are rapidly becoming the new norm.

As grizzly bears disappear into high-country dens to undertake the annual miracle of hibernation, we need to pause for reflection. What kind of world will we dream for grizzly bears this winter? What sort of world will grizzly bears wake up to next spring? Will it be a world in which wonder is diminished or renewed?


Louisa Willcox is a longtime grizzly bear activist and founder of Grizzly Times. She lives in Montana.