A deficiency of vitamin A is not only disease causing, but it can kill. On the other hand, overdoses of vitamin A are also lethal. The livers of certain animals, especially those adapted to polar environments, often contain amounts of vitamin A that would be toxic to humans. The first documented death due to vitamin A poisioning was Xavier Mertz, a Swiss scientist who died in January 1913 on an Antarctic expedition that had lost its food supplies and fell to eating its sled dogs. Mertz consumed lethal amounts of vitamin A by eating sled dog liver. The liver of the polar bear also has enough vitamin A to kill a human being.

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Vitamin A is a fat-soluble vitamin, which means that excess amounts cannot be easily eliminated from the body. On the other hand, water-soluble vitamins can be easily excreted from the body, so taking a little extra of them does no harm. Of all the vitamins, A, D, E and K are fat-soluble and B-complex and C are water-soluble.