The liver of mammals, fowl, and fish is commonly eaten as food by humans . Pork, lamb, veal, beef, 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. Daily consumption of liver can be harmful; for instance, vitamin A toxicity has been proven to cause medical issues to babies born of pregnant mothers who consumed too much vitamin A. 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. Liver contains large amounts of vitamin B12, and this was one of the factors that led to the discovery of the vitamin.