Vitamin A is a group of compounds that aids in vision, bone growth, reproduction, cell division, and cell differentiation. It helps the immune system fight off infections and disease. 

It is found in food sources such as carrots, milk, eggs, liver, peppers, oranges, spinach, and more . 

 The recommended intake of Vitamin A varies between different people of different ages, but overall an average healthy dosage is about 3000 ICU.  To get this much Vitamin A per day, you need to eat a balanced diet with nutrient rich food. 

Vitamin A deficiency can occur if the average dosage is not met, which usually does not happen in the United States, but can be a problem in some other countries.  Vitamin A deficiency causes night blindness, because your eyes do not receive enough Vitamin A to be healthy.  If deficiency occurs long enough, you can die because your immune system will not function well enough to fight off infections. 

People will Celiac disease, Crohn's disease, and pancreatic disorders are at risk of Vitamin A deficiency because they do not absorb as much vitamins as most people. 

 One issue surrounding Vitamin A is an experiment that was done to find out if Beta-Carotene (a nutrient that is often found with Vitamin A) actually helps prevent cancer.  The experiment concluded that Beta-Carotene actually increases the risk of getting lung cancer, making Beta-Carotene supplements not advisable for the general population. 

Vitamin A can also be unhealthy if too much is stored in the body.  This is called Hypervitaminosis A, and it causes toxic effects on the body if it occurs.

References

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.http://dietary-supplements.info.nih.gov/factsheets/vitamina.asp

http://lpi.oregonstate.edu/infocenter/vitamins/vitaminA/

http://www.nlm.nih.gov/medlineplus/ency/article/002400.htm

http://healthlink.mcw.edu/article/980793489.html

http://ohioline.osu.edu/hyg-Fact/5000/5551.html

http://www.vivo.colostate.edu/hbooks/pathphys/misc_topics/vitamina.html

http://www.whfoods.com/genpage.php?tname=nutrient&dbid=106

http://www.anyvitamins.com/vitamin-a-info.htm

http://www.vitamins-supplements.org/vitamin-A.php

http://www.ansci.cornell.edu/courses/as625/625vita.html

http://www.indiadiets.com/foods/food_nutrients/vitamins/Vitamin_A.htm

http://www.niams.nih.gov/Health_Info/Bone/Bone_Health/Nutrition/vitamin_a.asp

http://www.wrongdiagnosis.com/v/vitamin_a_deficiency/causes.htm

http://www.who.int/nutrition/topics/vad/en/

http://cebp.aacrjournals.org/cgi/content/full/13/1/40