Vitamin A is important for normal vision, adequate growth, and for cell division and differentiation. Vitamin A is essential for immune system function because it is necessary for the production of white blood cells that help fight infections. You also need vitamin A for healthy skin and mucous membranes.
Vitamin A deficiency is rarely seen in developed countries, but can result in visual problems and loss of normal immune system function.
Daily Requirements
Males
1 to 3 years: 300 mcg per day
4 to 8 years: 400 mcg per day
9 to 13 years: 600 mcg per day
14+ years: 900 mcg per day
Females
1 to 3 years: 300 mcg per day4 to 8 years: 400 mcg per day
9 to 13 years: 600 mcg per day
14+ years: 700 mcg per day
Vitamin A is found in both plant and animal sources. Preformed vitamin A, or retinol, is found in butter, egg yolks, fish, liver, meats and whole milk. Plant sources of vitamin A are called provitamin A carotenoids and include beta-carotene, alpha-carotene, and beta-cryptoxanthin. Carotenoids are found in dark green and yellow vegetables, as well as orange fruits and vegetables.
Taking vitamin A supplements, such as as beta carotene, has been recommended for preventing cancer; however, there is no evidence for this recommendation. In the case of cigarette smokers, taking beta carotene supplements may increase one's risk of cancer.
Taking large doses of preformed vitamin A supplements for extended periods of time may result in vitamin A toxicity, so the Institute of Medicine determined tolerable upper levels to be 3000 mcg per day. Vitamin A toxicity may result in birth defects, liver abnormalities, and reduced bone mineral density that may result in osteoporosis.
Sources:
"Vitamin A." Accessed March 17, 2009. http://ods.od.nih.gov/factsheets/vitamina/
Otten JJ, Hellwig JP, Meyers LD. "Dietary Reference Intakes: The Essential Guide to Nutrient Requirements." IOM, 2006.
