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Vitamin A
Definition
Vitamin A is a fat-soluble vitamin.
Alternative Names
Retinol; Retinal; Retinoic acid; Carotenoids
Function
Vitamin A helps form and maintain healthy skin, teeth, skeletal and soft tissue, mucus membranes, and skin. It is also known as retinol because it produces the pigments in the retina of the eye.
Vitamin A promotes good vision, especially in low light. It may also be needed for reproduction and breast-feeding.
Retinol is an active form of vitamin A. It is found in animal liver, whole milk, and some fortified foods.
Carotenoids are dark-colored dyes (pigments) found in plant foods that can turn into a form of vitamin A. There are more than 500 known carotenoids. One such carotenoid is beta-carotene.
- Beta-carotene is an antioxidant. Antioxidants protect cells from damage caused by substances called free radicals. Free radicals are believed to contribute to certain chronic diseases and play a role in the aging processes.
- Food sources of carotenoids such as beta-carotene may reduce the risk for cancer.
- Beta-carotene supplements do not seem to reduce cancer risk.
Food Sources
Vitamin A comes from animal sources, such as eggs, meat, fortified milk, cheese, cream, liver, kidney, cod, and halibut fish oil. However, all of these sources -- except for skim milk that has been fortified with Vitamin A -- are high in saturated fat and cholesterol.
Sources of beta-carotene include:
- Bright yellow and orange fruits such as cantaloupe, pink grapefruit, and apricots
- Vegetables such as carrots, pumpkin, sweet potatoes, and winter squash
- Other sources of beta-carotene include broccoli, spinach, and most dark green, leafy vegetables.
The more intense the color of a fruit or vegetable, the higher the beta-carotene content. Vegetable sources of beta-carotene are fat- and cholesterol-free.
Side Effects
If you don't get enough vitamin A, you are more likely to get infectious diseases and vision problems.
If you get too much vitamin A, you can become sick. Large doses of vitamin A can also cause birth defects.
Acute vitamin A poisoning usually occurs when an adult takes several hundred thousand IUs of vitamin A. Symptoms of chronic vitamin A poisoning may occur in adults who regularly take more than 25,000 IU a day. Babies and children are more sensitive to vitamin A, and can become sick after taking smaller doses of vitamin A or vitamin A-containing products such as retinol (found in skin creams).
See also: Hypervitaminosis A
Large amounts of beta-carotene will not make you sick. However, increased amounts of beta-carotene can turn the skin yellow or orange. The skin color will return to normal once you reduce your intake of beta-carotene.
Recommendations
The best way to get the daily requirement of essential vitamins is to eat a wide variety of fruits, vegetables, fortified dairy foods, legumes (dried beans), lentils, and whole grains.
The Food and Nutrition Board of the Institute of Medicine -- Dietary Reference Intakes (DRIs) Recommended Intakes for Individuals of Vitamin A:
Infants (average intake)
- 0 - 6 months: 400 micrograms per day (mcg/day)
- 7 - 12 months: 500 mcg/day
The Recommended Dietary Allowance (RDA) for vitamins is how much of each vitamin most people should get each day. The RDA for vitamins may be used as goals for each person.
Children (RDA)
- 1 - 3 years: 300 mcg/day
- 4 - 8 years: 400 mcg/day
- 9 - 13 years: 600 mcg/day
Adolescents and Adults (RDA)
- Males age 14 and older: 900 mcg/day
- Females age 14 and older: 700 mcg/day
How much of each vitamin you need depends on your age and gender. Other factors, such as pregnancy and your health, are also important. Ask your doctor what dose is best for you.
References
Sarubin Fragaakis A, Thomson C. The Health Professional's Guide to Popular Dietary Supplements. 3rd ed. Chicago, IL: American Dietetic Association, 2007.
Hamrick I, Counts SH. Vitamin and mineral supplements. Wellness and Prevention. December 2008:35(4);729-747.
Mason JB. Vitamins, trace minerals, and other micronutrients. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 237.
Reviewed By: Alison Evert, MS, RD, CDE, Nutritionist, University of Washington Medical Center Diabetes Care Center, Seattle, Washington. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
