Bears and Diabetes
Eric Chivian, MD, is the founder and Director of the Center for Health and the Global Environment at Harvard Medical School. In 1980, he co-founded, with three other Harvard faculty members, International Physicians for the Prevention of Nuclear War, which won the 1985 Nobel Peace Prize. Aaron Bernstein, MD has been affiliated with the Center for Health and the Global Environment since 2001 and is currently a resident in the Boston Combined Residency in Pediatrics. Together they wrote Sustaining Life: How Human Health Depends on Biodiversity which presents a comprehensive review of how human medicines, biomedical research, the emergence and spread of infectious diseases, and the production of food all depend on biodiversity. Chivian was recently interview on Canada’s The Hour, you can watch him here. In the excerpt below from the book we learn more about the importance of Polar Bears.
Nine species of bears are listed on the IUCN’s 206 Red List of Threatened Animal Species, including the Polar Bear (Ursus maritimus), the Giant Panda (Alluropoda melanoleuca) and the Asiatic Black Bear (Ursus thibetanus). In 2005, the Polar Bear Specialist Group of the IUCN Species Survival Commission reviewed the status of the Polar Bear and decided to list it as a Vulnerable species, increasing its degree of threat from Lower Risk, given the projected loss of habitat resulting from global climate change. And in 2006, the U.S. Fish and Wildlife Service began a review to consider whether Polar Bears should also be protected under the Endangered Species Act, a decision that is expected in early 2008. Influencing this decision will be a series of studies released in September 2007 by the U.S. Geological Survey predicting that two-thirds of the world’s Polar Bears will be lost by 2050 because of melting summer sea ice in the Arctic secondary to global warming. These predictions are based on middle-of-the-road warming projections…
…Polar Bears are at great risk because they face a variety of environmental assaults. Some scientists predict that they, the larges carnivores on land…will be extinct in the wild by the end of the twenty-first century, and perhaps even earlier, due to the disappearance of the Arctic sea ice upon which they depend. Like other bears, Polar Bears are threatened by habitat loss. They are also killed by hunters, both for their meat (for human consumption and for dog food) and to make rugs and clothes, and by trophy hunters, who pay $20,000 or more for the chance to shoot a Polar Bear. While such hunting is tightly regulated by the United States and Canada (though banned in Norway), there is concern that overhunting may be threatening Polar Bear populations in some areas, such as Baffin Bay (between Canada and Greenland), parts of Chukchi Sea (north of the Bering Strait, between Siberia and Alaska), and parts of Russia. Polar Bears are especially threatened by the accumulation of high concentrations of pollutants in their tissues and by global warming. In addition, because of increasing oil and gas exploration and transport in the Artic, they may be exposed to a greater number of oil spills into the marine environment and to habitat alteration from increased shipping….
Diabetes Types 1 and 2 and Obesity
…Denning Black Bears have low blood levels of insulin, as do people with who suffer from type 1 diabetes (also called juvenile-onset diabetes) who are unable to produce enough insulin to control the amount of sugar in their blood. But unlike type 1 diabetics, denning bears do not develop the consequences of inadequate insulin-high blood sugar concentrations, dehydrations, and a condition called ketoacidosis. Ketoacidosis is a toxic state where circulating levels of ketones, products of fat metabolism, are high. Studies have confirmed that denning Black Bears keep their blood glucose levels normal despite not having enough circulating insulin. Ketoacidosis also does not occur, because free fatty acids, rather than being metabolized into ketons, are instead recycled back into triglycerides. Within these complex pathways in the denning Black Bear, there may be found new approaches for treating type 1 diabetes mellitus.
Free-ranging wild Polar Bears, by contrast, have been shown to be insulin-resistant, with fat bears (e.g., those reading for denning) having higher concentrations of insulin and higher levels of insulin resistance, than thinner bears. In humans, insulin resistance is also correlated with obesity. With the recent epidemic of obesity, particularly in countries such as the United States, where about one-third of all adults were considered obese in a study done in 2004, there is an associated epidemic of type 2 diabetes, an illness characterized by insulin resistance, with or without impaired insulin secretion…
…Under normal conditions in people, fat and carbohydrates compete as fuels for energy metabolism, with the contributions that each makes primarily determined by the availability of carbohydrates and by insulin levels. Following a carbohydrate-rich meal, the level of insulin rises, promoting the storage and metabolism of carbohydrates and restricting the release and subsequent metabolism of fat molecules from body stores. Conversely, when the dietary supply of carbohydrates is scarce or absent and circulating insulin concentrations are low, the use of fat for energy is enhanced, while that of carbohydrates is reduced. In type 2 diabetes this regulation is disturbed–increased concentrations of insulin no longer suppress the release and metabolism of fat, and cells become insensitive to insulin’s effects on carbohydrate uptake. As a result, type 2 diabetics have high circulating blood lipids (fats) as well as high blood sugar concentrations and are at greater risk for atherosclerosis (the build up of cholesterol-laden plaques in the walls of arteries), heart attacks, and strokes.
Despite insulin resistance and obesity, Polar Bears do not show any signs of altered energy metabolism and continue to tightly regulate the release and metabolism of body fat for energy production, and they do not develop type 2 diabetes. Clarifying the mechanisms involved in energy metabolism in Polar Bears, particularly the regulation of lipid metabolism and use, should provide greater insights into the pathogenesis of type 2 diabetes and into more effective treatments for this disease.
One possible treatment may involve employing a substance in denning bears’ blood that has been shown to trigger the transition from a period of ravenous appetite, during the three months prior to denning, when bears consume several times their usual number of calories per day, to a period of fasting, just prior to denning, when bears are no longer hungry and stop eating. In the fasting state, bears begin urea recycling and start losing fat tissue, although they retain their lean body mass. Such a medicine might be effective in treating obesity, as well as type 2 diabetes associate with it.