Vitamin A and its precursor beta-carotene function in many different bodily systems and have been implicated in the prevention and treatment of specific diseases. The recommended intake of vitamin A is between 300 to 600 mcg daily for infants and children and between 700 to 1,300 mcg daily for adults, depending on age, gender and special circumstances such as pregnancy. Vitamin A works in concert with other vitamins, minerals and phytochemicals in the body to help maintain normal cellular function.
Vitamin A Types
Vitamin A is actually a group of many different compounds called retinoids, according to the Linus Pauling Institute at Oregon State University. These retinoids include retinol, retinal and retinoic acid. Beta-carotene is a type of carotenoid that can be converted by the body into retinol, one of the variants of vitamin A. Beta-carotene and its fellow carotenoids alpha-carotene and beta-cryptoxanthin, which share the same ability, are called provitamin A carotenoids.
Physiological Effects
Retinol, the variant of vitamin A that is made from beta-carotene, operates in the retina of the eye, where it helps rod cells function. One of the jobs of rod cells is to detect small amounts of light. Because of its effect on rod cells, retinol is necessary for night vision. Beta-carotene also functions as an antioxidant in the body. Another vitamin A type, retinoic acid, plays a role in gene expression. The different forms of vitamin A also operate in fetal development, immunity and red blood cell production.
Uses
According to Medline Plus, research on beta-carotene intake has found that consuming food or supplements high in beta-carotene is an effective treatment for sun sensitivity in people with the disease erythropoietic protoporphyria. Consuming a supplement with 15 mg of beta-carotene in conjunction with zinc, vitamin C and vitamin E can help slow the progression of advanced age-related macular degeneration. Other potential uses of beta-carotene that seem promising, but still need further study, include its use as a treatment for existing osteoarthritis and for preventing exercise-induced asthma attacks. Beta-carotene might also reduce the risk of breast and ovarian cancers and improve breathing in smokers.
Sources
Vitamin A is most commonly found in plant foods as its precursor beta-carotene, often along with other carotenoids. Beta-carotene has an orange-red pigmentation, so foods high in this vitamin precursor tend to be brightly colored. Examples include sweet potatoes, cantaloupe, pumpkin and carrots. Some animal-derived foods contain vitamin A in the form of retinol, including cod liver oil, fortified breakfast cereals, eggs and milk. Some green vegetables also contain carotenoids, including spinach, kale and broccoli.
Recommendations
The NIH Office of Dietary Supplements recommends that vitamin A and beta-carotene consumption be primarily in the form of whole foods, as this encourages the simultaneous intake of other nutrients that may work in synergy with this vitamin. Supplements and fortified foods may be advisable for individuals with a risk of deficiency, such as children with measles, individuals with celiac disease or Crohn's disease and people with pancreatic disorders. These problems may affect the body's ability to adequately absorb vitamin A and carotenoids from food.
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