Polar bears are top carnivores that bioaccumulate the vitamin A produced by marine algae lower down the food chain. Because vitamin A isn’t water-soluble, it can’t be easily flushed from the body and is stored in the liver instead. Bears and seals have generally high levels of vitamin A in their livers but polar bears have the most of any animal.
The recommended daily allowance (RDA) for vitamin A in humans is 0.9mg, and you can get that from eating just one-tenth of a gram of the liver from a well-fed polar bear. The entire liver contains enough vitamin A to kill as many as 52 adults! If you spread it out and ate just enough to get your RDA every day, that liver would last you 143 years!