I was going to make a polar bear liver joke but google reminded me - that's not D - that's A.

Is it true that you cannot eat polar bear liver?

You could eat it. If you are lucky, you would live to regret it. That's because the liver could be lethal! You could overdose on retinol! That isn’t some bizarre toxin, retinol is just the chemical name for a form of vitamin A. Polar bears are carnivores, feeding mostly on seals. Lots of seals. Their hearty appetite is due to their need to accumulate lots of fat for insulation against the cold. Seals are rich in blubber. And where does their fat come from?

They feed on fish, squid, krill and other sea creatures which in turn feed on various types of plants ranging from seaweed to algae. These plants contain various carotenoids that concentrate up the food chain and serve as precursors for vitamin A. Since vitamin A is fat-soluble, it builds up in fatty tissue, particularly the liver. Polar bears have lots of fatty tissue, so they accumulate lots of vitamin A, particularly in their liver.

Like virtually any substance, vitamin A can be toxic in high doses. But polar bears have evolved to be unaffected by the higher doses of vitamin A, because its accumulation is a consequence of their need for a high-fat diet...