A Beary Long Winter


This winter really made me think hibernating animals had the right idea. I'd love to just sleep away the six-month cold front, and wake up as refreshed as ever. Now, as great as that sounds, there are a few minor things I'd have to worry about - you know, my heart stopping, bone loss, small things like that. I'm jealous of bears because they don't have to worry about any of that; they have so many cool adaptations that allow them to hibernate!

Let's start with their hearts. A recent study published in Physiological and Biochemical Zoology explains changes in Grizzly bear hearts as they hibernate, which protects them from potential complications from snoozing the next six months away. You can read the abstract here and the press release about the study here.

During hibernation, the heart rate of a Grizzly bear slows from an active 84 beats per minute to about 19 per minute. Just for comparison, the average resting human heart rate is about 70 beats per minute. Some extremely fit athletes may be able to get their rate down to the 40s, but this is pretty uncommon. So, 19 heart beats per minute... if this were to happen in a human, congestive heart failure would almost be inevitable. The study explains that such a slow beat causes blood to gather in all four chambers of the heart, and this pressure in humans would cause the chambers to stretch, making the heart weaker and less efficient. Bears can avoid this! According to the results of the study, a Grizzly bear's left ventricle stiffens to prevent the heart chambers from stretching, and to stop the atrium from working way too hard to force blood into the stiffened left ventricle, the heart beats slower and weaker. Once bears awake from their short nap, this process stops and the heart will go back to beating at its regular pace. This process is in part due to a protein called myosin, which can either be alpha or beta. The alpha version, which researchers found was the dominant form during hibernation, creates quick but weak contractions compared to the beta, causing the heart to beat weaker and slower, and therefore protecting the atrium.

As for bone loss and skeletal damage, bears and other large hibernating mammals can also prevent this! Seriously, bears are really cool. Anyway, this study, published in the American Journal of Physiology - Regulatory, Integrative and Comparative Physiology, shows that while smaller hibernating mammals may lose bone, bears may have evolved in a way to allow them to maintain their bone structure and recycle calcium. You know that phrase "use it or lose it?" Well, that's pretty applicable to bones, so how do the bears manage to not use it and keep it?

Hibernating grizzly figure 1.gif

The study suggests that bears can maintain "balanced bone remodeling," preventing bone loss from disuse. Bone resorption and formation remain balanced, meaning even though the bone is not being used and some bone minerals are being transferred from bone fluid into the blood (resorption), bone formation remains strong. In humans, there's a pattern: while in childhood, bone formation exceeds resorption, and as aging happens, resorption exceeds formation, which is why osteoporosis is more prevalent in older adults. Researchers say cortical bone is actually more mineralized in hibernating bears than in active bears, meaning proportionately, there is less mineral being lost from bone resorption while hibernating, resulting in bones maintaining their strength. Smaller hibernating mammals have been unable to obtain this adaptation. This balance between resorption and formation may explain why bone structure and strength are not different in hibernating and active bears.

More like this

Apart from the obvious app (the hibernating astronauts in "2001") I would like to be able to slow down the metabolism of cancer patients, making it possible to sequence the cancer genomes and pinpointing the precise medicine combo that is most likely to work on the tumors. And Dr House and his colleagues would also like to have more time for a diagnosis.

By Birger Johansson (not verified) on 24 Feb 2011 #permalink

This sort of thing has a lot of uses. Hibernating astronauts saving resources going to Mars, naturally. Hadn't thought of diagnostic and treatment time extension being in the mix but #1 certainly has a point.

If it wasn't too technically and materially challenging to do so I could see it as being useful in a mass casualty situation. Say, after an earthquake a place with eighty thousand people only has resources for seventy thousand. Put twenty thousand in hibernation and they use less than half as much water, food, etcetera. This frees up manpower and resources, while keep the people safe, perhaps gives them time to heal, and that allow repairs to go much more swiftly.

Yes, far fetched and unrealistic but we do stuff today that was science fiction thirty years ago. So lets go crazy.

How about hibernation prisons. A prison where most of the prisoners are in hibernation half the year? Fewer resources used means those remaining awake get more attention, treatments, rehabilitation. Those who need more guards get more guards. Costs go down, rehabilitation goes up, recidivism goes down, guards are safer and less stressed so they treat the prisoners better. Win-win.

The military would be interested. Lots of troops get sent off to remote locations where they sit and sit, waiting to be needed. Hibernation would allow them to be present and ready to go in a few days while limiting resource use and boredom.

Then there are the benefits of understanding bone and heart metabolism. The ability of an organism to turn on and off changes in the heart itself. The ability to maintain healthy bones without exercise. Sounds to me like these might be useful things to know because they might lead to potential drugs, therapies, treatments.

Lots of interesting paths this might take.

The military would be interested. Lots of troops get sent off to remote locations where they sit and sit, waiting to be needed. Hibernation would allow them to be present and ready to go in a few days while limiting resource use and boredom.