Polar Bear Liver

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Polar bears, along with other fish-eating carnivores of the polar regions, concentrate large amounts of vitamin A in their liver -- so much, in fact, that the livers of polar bears, seals, and even huskies can be toxic. Ingestion of polar bear livers and huskie livers has been reported to cause Hypervitaminosis A in Polar Explorers. Acute toxicity can result from ingesting more than 300,000 IU, which is only about 10-15g of polar bear liver.

Vitamin A levels (Retinol, IU/g) in the liver of various animals
Species n Average Maximum Reference
Polar Bear (Greenland) 3 16,300 18,000 Rohdal & Moore 1943
Polar Bear (Greenland) 2 24,300 26,700 Rohdal 1949
Polar Bear (Alaska) 2 32,600 34,600 Russell 1966
Polar Bear (Alaska) 14 22,100 30,400 Lewis & Lentfer 1967
Huskie 10 10,570 24,400 Southcott & Chesterfield 1971
Hooded Seal 40 3,000 24,000 Rohdal & Davies 1949
Greenland Seal 70 3,441 15,000 Rohdal & Davies 1949
Greenland Fox 1 na 12,000 Rohdal 1949
Atlantic grey Seal 1 na 1,550 Rohdal & Davies 1949
Southern Elephant Seal 2 1,160 1,240 Southcott & Chesterfield 1971
Weddell Seal 5 444 800 Southcott & Chesterfield 1971
Bowhead whale 1 na 4,320 Lewis & Lentfer 1967
Bearded seal 1 na 1,780 Lewis & Lentfer 1967
Ringed seal 1 na 2.450 Lewis & Lentfer 1967
Common seal 2 56 90 Rohdal & Davies 1949
Walrus ? "very small" na Rohdal 1949
Snow hare ? "very small" na Rohdal 1949
Domestic Cat 1 na 18 Russell 1966

NB: 1 international unit (iu) = 0.3 retinol equivalents (RE); 1 RE = 1 µg retinol = 0.0035 µmol retinol.

In 1949, Rodahl assessed the toxicity of polar bear liver by feeding it to rats:

In experiments on rats, ingestion of 0.5-0.6 gm polar bear liver daily proved toxic in all cases. In two cases, 0.5-0.7 gm polar bear liver daily proved lethal. Variouos fractions of the polar bear liver were given to different groups of rats with the following results. Polar bear liver freed of its vitamin A was non-toxic. Bear liver, bear liver oil contraining all of its vitamin A, and purified vitamin A concentrates, had identical effects when give in equivalent amounts with regard to the vitamin A content. Equivalent amounys of bear liver oil in which the vitamin A had been destroyed had no bad effects. The symptoms increased with increasing amounts of vitamin A...It is therefore confirmed that the toxic substance in polar bear liver is identical to vitamin A, and that ingestion of large quantities of polar bear liver leads to hypervitaminosis A.

References

Rodahl, K., and T. Moore. 1943. The vitamin A content and toxicity of bear and seal liver. Biochemical Journal 37:166­68. PMID 16747610

Rodahl, K. and A.W. Davies. 1949 Vitamin A in seals. Biochem J. 45:408-12. PMID 15394431

Rodahl, K. 1949. Toxicity of polar bear liver. Nature 164:530.

Russell, F. E. 1967. Vitamin A content of polar bear liver. Toxicon 5:61­62. PMID 6036254

Lewis, R. W., and J. A. Lentfer. 1967. The vitamin A content of polar bear liver: range and variability. Compar. Biochem. Physiol. 22:923-926.

Southcott R, Chesterfield N, Lugg D. Vitamin A content in the livers of huskies and some seals from Antarctic and subantarctic regions. Med J Aust 1971; 1: 311-313.