Liver has long been a staple in many diets. Deep-fried chicken livers are a favorite in parts of the American South. Travel to Germany and you can feast on traditional liverwurst. In Japan, you can order a heaping helping of sashimi made with raw fish liver. As delicious (or disgusting) as some of these dishes may sound to you, not every bird, fish or mammal necessarily offers the best ingredients for a culinary masterpiece. In fact, if you ever have the chance to try polar bear liver, think twice -- it may be the last meal you ever eat.
The native peoples of the Arctic have never shied away from cooking up some polar bear stew, but they've long known to avoid eating the livers of various arctic creatures. Western explorers, however, learned the hard way. As early as 1596, explorers returned to Europe with accounts of horrible illnesses resulting from the consumption of polar bear liver [source: Rodahl and Moore].
Illness severity depended on how much liver the explorers consumed, but symptoms typically included drowsiness, sluggishness, irritability, severe headache, bone pain, blurred vision and vomiting. Perhaps the most horrific symptom they encountered was peeling skin. While milder cases merely involved flaking around the mouth, some accounts reported cases of full-body skin loss. Even the thick skin on the bottoms of a patient's feet could peel away, leaving the underlying flesh bloody and exposed. The worst cases ended in liver damage, hemorrhage, coma and death.
These explorers suffered from acute hypervitaminosis A, a condition resulting from the overconsumption of vitamin A during a short period of time. The polar bear's liver, much like those of arctic seals and huskies, contains extremely high levels of retinol (the form of vitamin A found in members of the animal kingdom).
On the next page, we'll discover why polar bears carry around so much vitamin A in their livers and how crucial their retinol tolerance is to their survival.
Vitamin A in Polar Bear Liver
Vitamin A is a crucial building block for many animals. Humans only require it in very small amounts, but it plays a vital role in eyesight, reproduction, fetal development, growth, immune response and the cellular formation of tissue. We typically absorb it through the consumption of foods such as spinach, broccoli, eggs, milk and various meats. Vitamin A tolerability in humans varies depending on age, gender and physical condition. Your own personal tolerable upper limit depends on how efficient your enzyme system is, and how efficient your liver is at storing vitamin A. While the tolerable upper limit for healthy adults is set at 10,000 IU, signs of toxicity generally occur when approximately 25,000 to 33,000 IU are consumed [source: Higdon].
Without enough vitamin A in your system, you could easily find yourself facing symptoms just as bad as those associated with hypervitaminosis A. Deficiencies can lead to dry skin, diarrhea, blindness, growth retardation and even death.
Polar bears aren't immune to the dangers of consuming too much or too little vitamin A; they're affected just as severely by excess or deficiency. The only difference is that polar bears have a much higher tolerance for vitamin A. For instance, a healthy human liver contains 575 international units (IU) of vitamin A per gram while a polar bear's liver contains between 24,000 and 35,000 IU per gram [source: Eliasen]. Compare that to the tolerable upper level of vitamin A intake for a healthy adult human: 10,000 IU [source: Higdon].
Like many animals, polar bears benefit from keeping a certain amount of vitamin A in their system, but there's nothing to indicate they actually require such large quantities. In fact, their physiology evolved to tolerate so much vitamin A for only one reason: to eat seals.
In the wild, polar bears feed almost exclusively on bearded seals and ringed seals, both of which store high levels of vitamin A in their livers and blubber. If you ate a bearded seal's liver, you'd suffer from hypervitaminosis A, but the polar bear can tolerate and enjoy the feast. The seals store high levels of vitamin A in order to swiftly grow and nourish their young in a harsh, chilly environment. Remember, vitamin A plays a key role in growth and natal development. The seals rely on this vitamin to quickly advance them through their vulnerable pup stages.
So if the blue plate special at your favorite diner is ever sautéed polar bear liver, you might just want to stick with a salad. Explore the links on the next page to learn more about vitamin A and polar bear liver.
Related HowStuffWorks Articles
More Great Links
- AZA Bear Tag. "Polar Bear (Ursus maritimus)." Association of Zoos and Aquariums Standardizes Animal Care Guidelines. 2007. (June 25, 2008) http://www.polarbearsinternational.org/rsrc/FinalPolarBearSG2007.pdf
- Brown, Dan. "Vitamin A Toxicity." Cornell University Department of Animal Science. (June 25, 2008) http://www.ansci.cornell.edu/courses/as625/625vita.html
- "Calories in Peeling Hard Boiled Eggs." Calorie-Count. 2008. (June 25, 2008) http://www.calorie-count.com/calories/item/83271.html
- Eliasen, Mogens. "The Dangerous(?) Vitamin A." K9joy Education. May 2, 2005. (June 25, 2008) http://k9joy.com/dogarticles/vitaminA.php
- Hicks, R. Marian. "The scientific basis for regarding vitamin A and its analogues as anti-carcinogenic agents." Proceedings of the Nutrition Society. 1983. http://journals.cambridge.org/download.php?file=%2FPNS%2FPNS42_01% 2FS0029665183000142a.pdf&code=e4ce569b2b8189bd533e435a6523a1b7
- Higdon, Jane. "Vitamin A." Linus Pauling Institute at Oregon State University. 2007. (June 25, 2008) http://lpi.oregonstate.edu/infocenter/vitamins/vitaminA/
- "Hypervitaminosis A." Medline Plus. Aug. 8, 2006. (June 25, 2008) http://www.nlm.nih.gov/medlineplus/ency/article/000350.htm
- International federation of Competitive Eating. (June 25, 2008) http://www.ifoce.com/records.php
- Lintzenich, Barbara, et al. "Formulating Diets for Polar Bears in Captivity." Brookfield Zoo Conservation Biology and Research Center. http://www.polarbearsinternational.org/pbhc/lintzenich.htm
- Mos, Lizzy and Peter S. Ross. "Vitamin A physiology in the precocious harbor seal (Phoca vitulina): A tissue-based biomarker approach." Canadian Journal of Zoology. September 2002. http://www.ingentaconnect.com/content/nrc/cjz/2002/00000080/00000009/art00003
- Penniston, Kristina L. and Sherry A. Tanumihardjo. "The acute and chronic toxic effects of vitamin A." The American Journal of Clinical Nutrition. 2006. http://www.ajcn.org/cgi/content/abstract/83/2/191
- Rodahl, K. and T. Moore. "The Vitamin A Content and Toxicity of Bear and Seal Liver." The University of Cambridge Dunn Nutritional Laboratory and Medical Research Council. 1942. http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1257872
- Slaughter, Kip. E-mail interview. Conducted June 26, 2008.
- "Vitamin A." Britannica Online Encyclopedia. 2008. (June 25, 2008) http://www.britannica.com/EBchecked/topic/630964/vitamin-A