Tuesday, May 22, 2012

Doctor Pooh: The Use of Bears in Medicine


Bears have been an important part of our history, dating back to the earliest civilizations where they were integrated into religion and medicine.  Although they have less of a central role in modern religious and cultural practices, their importance in medicine is just as significant as ever.  In particular, studying the physiological processes bears undergo while denning is useful for understanding common diseases among humans, such as osteoporosis, renal disease, and diabetes.  Bears are also used for direct medicinal purposes by those who continue to practice traditional Chinese medicine.
Ursus americanus http://www.flickr.com/photos/chrisdoddsphoto/5543275903/
During the colder months when food is scarce, most bear species begin a period of hibernation lasting three to five months.  Hibernation is a relatively uncommon behavior, developed as an adaptation for surviving prolonged periods of harsh conditions. During these times, animals become unresponsive and drastically lower their body temperatures and metabolic rates.  Bears on the other hand, maintain their normal body temperature and are alert to potential dangers around them.  For this reason, this bear behavior is referred to as denning.  While denning, bears are immobile, and do not eat, drink, urinate or defecate.  Their ability to continue to regulate essential physiological processes is therefore quite impressive.   Studying the physiology of denning bears has been of great significance for researchers trying to understand human diseases associated with immobility, such as osteoporosis.

Osteoporosis occurs when the rate of bone reabsorption exceeds that of bone formation, and can be caused by disuse or changes in bone mineral density.  Although the bones of denning bears endure long periods of disuse, they never develop osteoporosis.  Research with the American black bear, Ursus americanus, has shown that while other hibernating animals undergo bone loss, bears simply undergo high rates of bone turnover, with increases in both the rates of formation and reabsorption.  Since bears do not urinate or defecate during hibernation, it is thought that the blood calcium concentrations remain stable and interact with calcium hormones and other growth factors to increase the rate of bone growth. The accelerated rate is then equivalent to the higher rate of loss associated with disuse.    Studies have also found that unlike humans, bears exhibit no significant increase in porosity with age or inactivity, and instead increase cortical bone bending strength.  By studying the physiological processes responsible for these phenomena, new treatments and preventative medicines may be created for human use against osteoporosis.

Changes in percentage of porosity in humans and black bears with age
Donahue, et al. 2006

Porosity in cortical bone. A) active bear B) bear in hibernation
6 Donahue et al. 2006
Similarly, studying polar bears is also valuable for learning about diabetes.  Like humans with Type 2 diabetes, polar bears are resistant to insulin, meaning higher concentrations of insulin in the body do not effectively metabolize carbohydrates or suppress the release and metabolism of stored fat.  In humans with type 2 diabetes, this process causes an increase in blood sugar and blood lipid concentration, which creates greater risk of atherosclerosis.  Polar bears however, are still able to effectively metabolize carbohydrates and regulate lipid release, even with high insulin concentration and insulin resistance associated with their pre-denning state.  Successful treatments for type 2 diabetes could be discovered with increased knowledge of the polar bear's metabolic pathway.  Unfortunately, due to the vulnerable state of their species, research is near impossible.

One reason why studies of the American black bear have been successful is the availability of animals.  American black bear populations are listed as Least Concern on the IUCN's Red List of Threatened species, and populations have generally been increasing across the United States and Canada.  The opposite is true for the polar bear, which are now listed as Vulnerable with declining populations.  The primary cause is shrinking ice sheets caused by global warming, which have caused a decrease in habitat and resulted in increased energy expenditure while traveling farther distances. 

Unfortunately, human threat to bears doesn't end with habitat destruction.  Asiatic black bears, Ursus thibetanus, face an additional threat: hunting and commercial trade.  These bears are primarily captured for the use of their gall bladder and bile, which are used in traditional Chinese medicine to treat pain, inflammation, protect the liver, and break up gall stones. Although alternative synthetics have been created and equivalent plants and herbs have been discovered, there is still relatively high demand among the wealthy and those who are distrusting of modern medicine.  
Ursus thibetanus http://www.arkive.org/asiatic-black-bear/ursus-thibetanus/
As a way of preventing Asiatic black bears from increasing their status from Vulnerable to Endangered while meeting the demand for bile, commercial bear farming was introduced in China in 1984. These businesses still significantly impact wild bear populations through the repeated capture of wild bears in order to stock and maintain the supply of bile.  Some farms have claimed to breed individuals to reduce population decline, however, most do not make any attempt at husbandry.  Today there are approximately 14,000 bears held in captivity for this purpose.  Furthermore, the methods used for capture, captivity, and bile extraction are extremely detrimental to the health of the bears.  The animals are all kept in small metal cages, some of which completely restrict movement.  Many individuals are missing paws or large sections of limbs as a result of trapping methods.  Those with wounds are often untreated and develop infections.  The bile is extracted regularly through an implanted tube, metal catheters, or through a permanent hole in the abdomen to the gall bladder.  Bears often develop infections from the holes pierced through their abdomen and can endure complications when bile bleeds back into their body.  These processes are all quite painful, as bears have been observed chewing their paws or uttering distressing sounds.  Many have broken teeth and bleeding mouths from repeatedly biting at the cages.

Captive bear on bile farm http://www.myspace.com/MikalynME/photos/12620456#{%22ImageId%22%3A12620456}
However, there is hope for these bears.  Organizations like Animals Asia are working to eliminate bear farming practices. It is a constant struggle between the animals' unrecognized right to live free from torture against the human sense of entitlement.  Although there is great value in traditional medicines from nature in terms of health benefits and heritage, sometimes the cost is too great.  The use of bears in medicine can be a fantastic tool, but it should not come at the expense of individuals or the species.  These species are important for preserving biodiversity, ecosystem health, and most importantly, an intrinsic right to exist.  There is also much that we can learn from bears regarding the biological processes associated with common diseases.  For these reasons, we should actively work to improve the health of current populations and preserve all species of bears by reducing habitat destruction and eliminating poaching and bile farming.


(2012, Feb. 20). Medicinal Value of Bear Bile. Retrieved from http://www.china.org.cn/video/2012-02/20/content_24679572.htm.

(2010, Nov. 8). Osteoporosis: Thin Bones. Retrieved from http://www.ncbi.nlm.nih.gov/ pubmedhealth/PMH0001400/

Bernstein, A. & Chivian, E. (2008). Sustaining Life: How Human Health Depends on Biodiversity. Oxford, NY: Oxford University Press

Donahue, S. W., McGee, M. E., Harvey, K. B., Vaughan, M. R. & Robbins, C. T. (2006). Hibernating bears as a model for preventing disuse osteoporosis. Journal of Biomechanics, 39(8), 1480-1488.

Donahue, S. W., Galley, S. A., Vaughan, M. R., Patterson-Buckendahl, P., Demers, L. M., Vance, J. L. & McGee, M. E. (2006). Parathyroid hormone may maintain bone formation in hibernating black bears (Ursus americanus) to prevent disuse osteoporosis. Journal of Experimental Biology, 209, 1630-1638.

Garshelis, D.L. & Steinmetz, R. 2008. Ursus thibetanus. In: IUCN 2011. IUCN Red List of Threatened Species. Version 2011.2. <www.iucnredlist.org>. Downloaded on 20 May 2012.

No comments:

Post a Comment