The liver of mammals, fowl, and fish is commonly eaten as food by humans. Domestic pig, lamb, calf, ox, chicken, goose, and cod livers are widely available from butchers and supermarkets while stingray and burbot livers are common in some European countries. Animal livers are rich in iron, copper, the B vitamins and preformed vitamin A. It is unsure if daily consumption of liver can be harmful, as no conclusive research has been done on the toxicity of preformed vitamin A from food. A single serving of beef liver exceeds the tolerable upper intake level of vitamin A. 100 g cod liver contains 5 mg of vitamin A and 100 µg of vitamin D.
Some fish livers are valued as food, especially the stingray liver. It is used to prepare delicacies, such as poached skate liver on toast in England, as well as the beignets de foie de raie and foie de raie en croute in French cuisine. Cod liver is a popular spread for bread or toast in several European countries. In Russia, it is served with potatoes. Cod liver oil is commonly used as a dietary supplement. Liver of burbot is eaten in Finland: it is common for fish vendors and supermarket fish aisles to sell these fish with liver and roe sacks still attached. These parts are often eaten boiled or added to burbot soup. Burbot and its liver are a traditional winter food.
Poisoning
Very high doses of vitamin A have the potential to be toxic and can cause hypervitaminosis A, a dangerous disorder. There have been several anecdotal reports and a few scientific studies of vitamin A poisoning due to the consumption of the livers of polar bears, walruses, bearded seals, moose, and huskies. The livers of these animals can contain very high levels of vitamin A. The Inuit will not eat the liver of polar bears or bearded seals. It has been estimated that consumption of 500 grams of polar bear liver would result in a toxic dose for a human. Russian sailor Alexander Konrad, who accompanied explorerValerian Albanov in a tragic ordeal over the Arctic ice in 1912, wrote about the awful effects of consuming polar bear liver. Also, in 1913, Antarctic explorers on the Far Eastern PartyDouglas Mawson and Xavier Mertz were believed to have been poisoned, the latter fatally, from eating husky liver, though this has been contested recently. Vitamin A poisoning is less likely from consuming oil-based vitamin A products and liver than from consuming water-based and solid preparations. Mercury content in some species can also be an issue; in 2012 the Government of Nunavut warned pregnant women to avoid eating ringed seal liver due to elevated levels of mercury. The neurotoxin in the liver of the pufferfish contains the highest concentration of the tetrodotoxin, which characterizes the species. As a result, the liver has been illegal to serve since 1984.
