What should you do if you are out for a walk in the Arctic and you run across a bear? If it doesn't try to eat you, and if you do not have to eat the polar bear to survive, and polar bear is not a part of your family's traditional diet, I would suggest you should walk away slowly and leave the bear alone. Polar bears are dangerous, and are having a hard time due to global warming. Should you however be in a position of such desperation that you have to eat a polar bear to survive, then at least remember not to eat the the liver: polar bear liver contains toxic levels of vitamin A. You must not even feed it to the dogs.

Speaking of the dogs: if you should ever find yourself in a position in which you have to eat a husky to survive, you should remember not to eat the liver. Husky liver can contain toxic levels of vitamin A, although less than in polar bear liver.

Arctic foxes also store a lot of vitamin A in their livers.

All of which invites the obvious question: why do Arctic animals have livers full of vitamin A?

For polar bears, the answer is not hard to find: polar bears eat seals, and eat their livers, too. (If you should ever find yourself moved to eat a seal, you should follow the good example of the Inuit, not of the bear, and remember not to eat the liver. Seal liver contains toxic levels of vitamin A.)

However, the seals that polar bears eat are also Arctic animals, so this explanation doesn't get us very far. Let's gloss over some chemistry:

Vitamin A is a group of related compounds easily converted among themselves, which can find their way into an animal in either of two ways: the animal can eat them in their 'active' form, as retinoids such as retinol, when it eats another animal, or it can consume carotenoids such as beta-carotene in plants and convert them into the active forms itself.

Once vitamin A has entered an animal's bloodstream, the only way for it be removed is for it to be used: it is not water-soluble and cannot be extracted by the kidneys and excreted in the urine. Therefore it is stored in the liver until required and then released in small quantities. And therefore it accumulates in animals higher up the food chain.

The Arctic, as you may be aware, is not known for its verdant vegetation. Such vegetation as there is has a short growing season. Carotenoids are most abundant in fresh plant matter, and therefore are mainly fed into the food chain during a relatively short period of time. The same goes for the carotenoids entering the food chain under the Arctic ice where seals hunt: they come from algae, which require sunshine to grow. There is therefore evolutionary pressure on Arctic animals to be able to store vitamin A in larger quantities than animals at lower latitudes. More pressure arises from the fact that some animals go long periods without food, such as some species of seals when raising their young. And the Arctic food chain is quite simply longer: in less extreme climates, predators tend eat herbivores rather than other carnivores. But polar bears eat seals, which are themselves carnivores, much of whose diet is also composed of carnivores. And in general, if there aren't many plants around, animals are likely to eat other animals, and those animals are also likely to have been eating animals. And that is why Arctic animals tend to have toxic liver.

The last part of this explanation cannot apply to all animals, of course. The Arctic fox mainly eats lemmings, which are mainly vegetarian, and still contains impressive concentrations of vitamin A. But a fox is a smaller mystery than a bear.

Oh, and make sure you cook the meat thoroughly to kill any parasites. Polar bears are full of them.

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