Vitamin A

Vitamin A is a micronutrient.  It is required for two purposes:
*to replenish the molecules that detect low light and different colors of light in the retina.
*to allow the creation of chemicals that encourage the growth of epithelial cells, such as the skin
Vitamin A is found in both plants and animals, but in different chemical forms.  In addition, animals are a richer source of Vitamin A and vegans have to be particularly careful about getting enough in their diet.  The yellow pigments in vegetables are very high in Vitamin A. It can also be chemically synthesized.  In the human body, it is stored in fat and the liver.  Humans can create their own Vitamin A if they have the necessary precursors in their diet.
Naturally, animal liver contains the most Vitamin A by weight, but it can also be found in dandelion greens (the richest plant source), carrots, broccoli, sweet potatoes, butter, kale, spinach, pumpkin, Cheddar cheese, cataloupe and eggs.
Vitamin A deficiency is one of the most common vitamin deficiencies in the world, affecting about one-third of the human population under the age of five (when the need for the vitamin is the highest).  In addition to skin and gene transcription problems, it also causes vision problems, starting with poor night vision which can progress to blindness.
However, it is also possible to overdose on Vitamin A, which causes Hypervitaminosis A.  This can start with liver problems and can progress to a wide variety of symptoms that are common to other diseases, making it a zebra diagnosis.  
Vitamin A at Wikipedia
Category:Nutrition