Do not eat polar bear liver. At least not the whole thing in one meal. This is because it contains so much vitamin A that it becomes toxic. It contains a form of vitamin A called retinol. Vitamin A is one of those vitamins that one can overdose on.
But can a person die from it? Article on HowStuffWorks asks the question “Will I die if I eat polar bear liver?” It depends on how much is eaten. But it does report that early Western explorers suffered from “acute hypervitaminosis A” from eating polar bear liver. They became drowsy, sluggish, and irritable. They have pains in their heads and bone. They vomit and their vision blurred, and their skins flaked. The severe cases had hemorrhaging and entire skins peeled off. Some went into coma and died.
Paper by Rodahl and Moore writes of vitamin A toxicity of bear and seal liver as experienced by Arctic explorers. It also tells of rodent experiments demonstrating some vitamin A toxicity effects in rats.
HuffingtonPost says that …
“In fact, the way the Inuit used to kill explorers in the Arctic was to feed them polar bear liver, which gave them toxic doses of vitamin A”
So yes, if one eats enough of it, one can die from it. Dr. Chopra says so on page 140 of his book “Dr. Chopra Says” …
“If eaten in one meal, polar bear liver can be deadly.”
How Much Vitamin A is toxic?
According to WebMd …
“Vitamin A is LIKELY SAFE for most people when taken by mouth in amounts less than 10,000 units per day”
That is for adult that is. For children, it should be less. And it is also dependent on your age, gender, size, and physical condition.
But most likely and speaking generally, it would not become toxic until 25,000 to 33,000 IU per day is reached.  A polar bear liver contains 24000 to 35000 IU per gram. So one gram of it is enough to be toxic.
Why Polar Bears Have So Much Vitamin A?
Vitamin A is a fat soluble vitamin. So it does not eliminate in urine. Instead it bio-accumulates in the fat of the liver. Many animals have vitamin A in their livers. Polar bears eats a lot of these animals (such as seals) and accumulate their vitamin A into their own liver.
 Vitamin A Toxicity
 Will I die if I eat polar bear liver? – HowStuffWorks.com
 The Vitamin A Content and Toxicity of Bear and Seal Liver
 Mark Hyman, MD: Vitamin D: Why You Are Probably NOT Getting Enough and How That Makes You Sick
 VITAMIN A: Uses, Side Effects, Interactions and Warnings – WebMD
 Linus Pauling Institute at Oregon State University
 Vitamin A in Polar Bear Liver