Vitamin A is a nutrient involved in many biological processes. Found naturally in a number of foods, vitamin A is also available in dietary supplement form, and is known to offer antioxidant effects.
Essential for good vision, vitamin A also aids the body in the formation and maintenance of skin, teeth, skeletal tissue, soft tissue, and mucus membranes.
An active form of vitamin A, the substance retinol produces the pigments found in the retina of the eye.
Vitamin A is found in many foods from animal sources, such as egg yolks, dairy products, and fish oil.
In addition, a wide range of fruits and vegetables contain pro-vitamin A carotenoids, a class of nutrients that your body converts to vitamin A.
Beta-carotene and alpha carotene are two of the most common pro-vitamin A carotenoids. Sources of pro-vitamin A carotenoids include:
- leafy greens
- sweet potatoes
Health Benefits of Vitamin A:
Here's a look at the science behind the health benefits of vitamin A:
Vitamin A may help protect against breast cancer, according to a 2011 report published in Cancer Causes & Control. In their analysis of 51 studies on the association between vitamins A, C, and E and breast cancer, the report's authors determined that a high intake of vitamin A could reduce breast cancer risk.
There is currently a lack of evidence supporting the use of vitamin A for prevention of other types of cancer. For instance, a 2011 report published in PLoS One found insufficient evidence that vitamin A can help prevent lung cancer. In addition, a 2004 review published in Lancet failed to find evidence that vitamin A can help prevent gastrointestinal cancers.
2) Eye Diseases
Vitamin A shows promise in the treatment of glaucoma, suggests a 2011 report published in the International Journal of Ophthalmology. According to the study's authors, vitamin A appears to prevent the oxidative stress known to promote the progression of glaucoma. The authors also note that cod liver oil (a substance containing both vitamin A and omega-3 fatty acids) may be particularly beneficial as a glaucoma treatment.
Research on the use of vitamin A in treatment or prevention of other eye disorders is fairly limited. However, there's some evidence that carotenoids like lutein and zeaxanthin may help fight cataracts and age-related macular degeneration.
3) Immune Function
Vitamin A may help stimulate the immune system, according to a 2007 report published in the Annals of Nutrition and Metabolism. The report's authors note that running low on vitamin A may weaken immune response, in turn, decrease your body's defense against infection.
Uses for Vitamin A Supplements
Vitamin A supplements are touted for the treatment of the following health conditions:
- age-related macular degeneration
- Crohn's disease
- cold sores/li>
- fibrocystic breast disease
- gum disease
- premenstrual syndrome
- sinus infections
- urinary tract infections
- vaginal infections
- yeast infections
In addition, vitamin A supplements are said to raise sperm count, promote wound healing, treat burns, slow up the aging process, boost the immune system, and protect against heart disease and some forms of cancer (such as breast cancer).
The recommended dietary allowance (RDA) of vitamin A is 700 mcg (2,333 IU) per day for most adult women and 900 mcg (3,000 IU) per day for men. According to the National Institutes of Health, the highest level of vitamin A intake that is likely to present no risk of toxic effects is 10,000 IU per day for most adults. However, chronic ingestion of even slightly higher doses of vitamin A may increase your risk of a number of serious health issues, including osteoporosis, liver toxicity, and vision problems.
In addition, there's some evidence that use of vitamin A supplements may increase cardiac mortality among men with heart disease.
The RDA for pregnant adult women is 770 mcg (2,565 IU) per day. Some studies suggest that congenital abnormalities may be more common in infants whose mothers took slightly excessive doses of vitamin A while pregnant.
Given these safety concerns, it's extremely crucial to take caution when increasing your intake of vitamin A, and to consult your primary health care provider.
It's important to note these recommendations are for preformed vitamin A, and do not include pro-vitamin A carotenoids (such as beta-carotene). Also known as retinol, preformed vitamin A is found in animal products, and is available in supplement form.
Signs of vitamin A toxicity include fatigue, nausea, and excessive sweating.
Where To Find Vitamin A Supplements
Widely available for purchase online, vitamin A supplements are sold in natural-foods stores, grocery stores, drugstores, and stores specializing in dietary supplements.
American Cancer Society. "Vitamin A, Retinoids, and Provitamin A Carotenoids." May 2012.
Bjelakovic G, Nikolova D, Simonetti RG, Gluud C. "Antioxidant supplements for prevention of gastrointestinal cancers: a systematic review and meta-analysis." Lancet. 2004 Oct 2-8;364(9441):1219-28.
Fritz H, Kennedy D, Fergusson D, Fernandes R, Doucette S, Cooley K, Seely A, Sagar S, Wong R, Seely D. "Vitamin A and retinoid derivatives for lung cancer: a systematic review and meta analysis." PLoS One. 2011;6(6):e21107.
Fulan H, Changxing J, Baina WY, Wencui Z, Chunqing L, Fan W, Dandan L, Dianjun S, Tong W, Da P, Yashuang Z. "Retinol, vitamins A, C, and E and breast cancer risk: a meta-analysis and meta-regression." Cancer Causes Control. 2011 Oct;22(10):1383-96.
Huang WB, Fan Q, Zhang XL. "Cod liver oil: a potential protective supplement for human glaucoma." Int J Ophthalmol. 2011;4(6):648-51.
National Institutes of Health. "Vitamin A: MedlinePlus Medical Encyclopedia." December 2012.
Wintergerst ES, Maggini S, Hornig DH. "Contribution of selected vitamins and trace elements to immune function." Ann Nutr Metab. 2007;51(4):301-23.