By Dr. Becker
Imagine spending, say, July and August eating yourself silly, and then on September 1, climbing into bed and falling asleep for the next six or seven months. You’d be a hot mess when you woke up in the spring, and not just from bed head.
You’d very likely be brewing some major health problems, everything from bedsores to muscle loss, weak bones, diabetes … even heart failure.
So what gives with bears? How is it they can sleep the winter months away, taking in not a morsel of food nor a drop of water and wake up in the spring in good health? It’s a hibernation thing, and it has intrigued scientists for decades.
A Bear’s Heart Rate Takes a Nosedive During Hibernation
Each year, scientists and other experts attend an annual event called the International Conference on Bear Research and Management. At a recent conference, researchers presented studies on the bear cardiovascular system, muscle chemistry, kidney function, fat storage and metabolism.
Cardiologist Dr. Peter Godsk Jorgensen of Copenhagen presented a study in which he was able to confirm earlier research that the heart rate of bears decreases tremendously during hibernation — from around 75 beats per minute to as few as 10. The pauses between beats can last 19 seconds or more.
As Godsk Jorgensen told the New York Times, “I once had a [human] patient with a pause of 13 seconds. When you have that, you go around and you faint and hit your head.”1
Using ultrasound imaging, the researchers also picked up clusters of blood cells called “smoke” around the bears’ healthy hearts. In humans, this “smoke” is seen in cases of severe heart failure or atrial fibrillation, which increases the risk for blood clots and stroke.
Hibernating Bears Don’t Eat, Drink, or Lose Muscle Mass
Dr. Ole Frobert, a Swedish cardiologist who works in collaboration with the Scandinavian Brown Bear Research Project, as well as scientists in Europe and the U.S., has uncovered remarkable differences in the physiology of hibernating vs. active bears.
Hibernating bears fatten themselves up during the summer months, and then don’t eat, drink, pee or poop during hibernation. Somehow, they maintain their muscle mass while lying perfectly still for several months.
Researchers also discovered the platelets in the bears’ blood become less sticky during hibernation. They act as natural blood thinners, which is probably nature’s way of preventing blood clots from forming during long stretches of inactivity.
The metabolism of hibernating bears drops to just 25 percent of its normal rate. The kidneys stop functioning altogether, yet the bears don’t suffer kidney failure.
Hibernation in Bears May Lead to Advances in Treating Human Obesity and Diabetes
The hibernation thing is of special interest to experts studying human obesity, which is associated with insulin resistance and Type 2 diabetes. Interestingly, bears are also insulin resistant, but do not develop diabetes.
Another presenter at the conference, Heiko Jansen, Ph.D. of the College of Veterinary Medicine at Washington State University, told The New York Times, “Obese bears are healthier; in fact, they are more reproductively fit. They have all the advantages, which is so counterintuitive to human biology.”2
How bear bodies handle insulin seems to be seasonal, with increases in resistance during hibernation and increases in sensitivity during warmer months.
When the researchers added blood serum from active bears (during the summer) to the fat cells of hibernating bears, the cells became more insulin sensitive. The secret sauce seems to be the serum.
Researchers hope their studies can ultimately lead to new ways to prevent obesity and treat diabetes in human patients. “We have to learn and relearn and relearn that nature has solved these problems,” says Jansen. “And it’s our job as primates to figure this out.”3
Did You Know Not All Bears Hibernate?
Including polar bears! With the exception of pregnant females, polar bears don’t do the hibernation thing like brown and black bears. Adult males and non-pregnant females are active year-round.
Pregnant females prepare a snow den, where they give birth and stay put with their cubs for three months. During this time, they live off their fat reserves, but they don’t actually hibernate because they need to maintain a normal body temperature to meet the physical demands of pregnancy, birth and nursing.