Vitamin A is important for normal vision, adequate growth, and for cell division and differentiation. It's 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.
