The liver of a polar bear, while a source of sustenance, can be fatal to humans if consumed. This toxicity has been known to Indigenous communities for centuries.
The Science Behind the Toxicity
The danger from polar bear liver stems from an exceptionally high concentration of preformed Vitamin A (retinol), leading to hypervitaminosis A. A polar bear’s liver can contain millions of International Units (IU) of Vitamin A, with values often between 24,000 and 35,000 IU per gram. For perspective, the recommended daily allowance for an adult human is 2,333 to 3,000 IU. Just 30 to 90 grams of polar bear liver can deliver 300,000 IU or more, enough to be acutely toxic.
The polar bear’s diet explains these levels. As apex predators, they consume seals, which are rich in Vitamin A. Since Vitamin A is fat-soluble and not easily excreted, it bioaccumulates in the liver, reaching extreme concentrations at the top of the food chain. Polar bears have evolved unique metabolic pathways to tolerate these levels, a capability humans lack.
Effects of Hypervitaminosis A on Humans
When humans consume highly concentrated Vitamin A from polar bear liver, acute poisoning symptoms can manifest rapidly, often within hours or days. Initial signs include severe headache, dizziness, nausea, and vomiting. Skin may also become dry, rough, and peel extensively. Other effects include drowsiness, irritability, blurred vision, and abdominal pain.
Historical accounts from early Arctic explorers serve as warnings of this toxicity. In 1597, Dutch explorer Gerrit de Veer documented his crew becoming severely ill with widespread skin peeling after eating polar bear liver. A case involving Antarctic explorers Douglas Mawson and Xavier Mertz in 1913 also describes severe symptoms, including delirium and skin desquamation, after consuming sled dog livers, which also accumulate high levels of Vitamin A.
Toxicity in Other Arctic Animals
High Vitamin A concentrations in the liver are not exclusive to polar bears; they extend to other Arctic predators within the marine food web. Animals such as bearded seals, walruses, Arctic foxes, and certain fish can also have dangerously elevated levels in their livers. This occurs because their diets include Vitamin A-rich marine organisms, causing the vitamin to accumulate through the food chain.
Sled dogs, which consume marine mammals, can also develop livers with toxic Vitamin A levels, posing a similar risk. While the liver of these animals is hazardous, their muscle meat is generally safe for consumption. The extreme concentration of Vitamin A is primarily localized within the liver, serving as a storage site.