Polar Bear Liver
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.
| 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.