benefits of vitamin A

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What is vitamin A?

Vitamin A is classified as an essential vitamin, which means the body cannot produce it.  You can get vitamin A through your diet in two different ways: through carotenoids found in fruits and vegetables, and through retinol found in animal products and supplements.  The difference between carotenoids and retinol is that retinol is the biologically active form of vitamin A, and carotenoids have to be converted into retinol in the body to be used. 

Where is vitamin A found?

Carotenoids can be found in many orange foods, such as carrots, sweet potatoes, squash, maize, papaya, and mangoes.  They can also be found in leafy green vegetables, red bell peppers, and tomatoes.  The absorption of vitamin A increases when these foods are served with a small amount of healthy fats; this is because vitamin A is a fat-soluble vitamin. 

The retinol form of vitamin A, or preformed vitamin A, can be found in small amounts in egg yolks and dairy products, and in high doses in liver.  Some vitamin-fortified foods may also contain retinol.

Why is vitamin A important?

Vitamin A plays many important roles in maintaining health.  Vitamin A is essential for good eyesight.  This is because it helps make rhodopsin – a protein that absorbs light in the retina. 

Vitamin A is also vital to skin health as it helps skin cell turnover, and topical retinol products are thought to be good for anti-aging.  In addition, a common treatment for severe acne is taking oral isotretinoin, which is a vitamin A derivative.  However, it is important to only take isotretinoin when prescribed by a doctor or dermatologist, as it can produce adverse side effects. 

Vitamin A plays a role in reproductive health and embryonic development, as it has been shown to be essential for the eye health of a developing embryo. 

Vitamin A is an integral part of a healthy immune system because it ensures that mucous membranes can effectively keep pathogens out of the body. 


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What is the RDA for vitamin A?

The Recommended Dietary Allowance (RDA) for vitamin A is 900mcg, or micrograms daily for men, 700mcg daily for women, and 770 and 1300mcg daily for pregnant and lactating women, respectively. 

The RDA for vitamin A is 500mcg for infants under 12 months, 300mcg for children 1-3 years of age, 400mcg for children 4-8 years of age, and 600mcg for children 9-13 years of age.  Breast milk generally contains enough vitamin A for infants six months of age and younger, and after that, small amounts of vitamin-A rich foods should be given as well.  Fortified infant formulas usually also contain vitamin A. 

These values are given by the National Institutes of Health, and the RDA represents the daily intake sufficient to meet the dietary needs of 97-98% of healthy individuals. Fortunately, some foods can help you reach this amount very easily; for example, just one baked sweet potato provides over 1,400mcg of vitamin A, or 156 percent of the daily RDA. 

How much is too much?

It is possible to have too much vitamin A.  Vitamin A is a fat-soluble vitamin, so it is not easily excreted out of the body like water-soluble vitamins would be.  For this reason, it is important to stay within the recommended Tolerable Upper Intake Level (UL) of 3,000mcg for adults, 600mcg for children 0-3 years of age, 900mcg for children 4-8 years of age, and 1,700mcg for children 9-13 years of age. 

The UL represents the maximum daily intake that is unlikely to cause negative health effects.  Exceeding this amount with preformed vitamin A can lead to significant toxicity.  Some studies have suggested that there is an association between too much preformed vitamin A and birth defects of the eyes, lungs, and heart, according to the NIH.  For this reason, it is not recommended for pregnant women to take high doses of vitamin A supplements.  Beta-carotene and carotenoids have not been shown to lead to birth defects, however, one study found that beta-carotene supplements were associated with an increased risk of lung cancer in male smokers.  An excess of beta-carotene can also lead to a reversible, harmless condition known as carotenodermia, where the skin turns a yellow-orange color. 

What are the benefits of vitamin A?

Some studies suggest that vitamin A might play a protective role in certain diseases.  Some studies suggest that one of the benefits of vitamin A is that it might prevent the progression of age-related macular degeneration (AMD).  A study found that patients with intermediate AMD that took a supplement containing beta carotene, zinc, and vitamins C and E had a decreased risk of developing advanced AMD. 

Vitamin A deficiency

Vitamin A deficiency is relatively uncommon in developed countries; however, it frequently occurs in low-income countries because people may not be able to afford fruits and vegetables rich in carotenoids.  

Vitamin A deficiency is particularly common in infants and breastfeeding or pregnant women because they have increased vitamin A needs.

Vitamin A deficiency can also affect those with cystic fibrosis – fat may not be absorbed well by these patients, which is important for vitamin A absorption.

Xerophthalmia can be a consequence of vitamin A deficiency – this condition is characterized by night blindness and poor lubrication in the cornea.  A deficiency in vitamin A can also have adverse effects on the immune system, which can increase the chances of illnesses caused by infections. 

Vitamin A supplementation

Fortunately, low vitamin A levels can be corrected with proper supplementation.  A review published in The Journal of Nutrition outlines the following public health practices to treat and prevent vitamin A deficiency in at-risk populations.  High doses of vitamin A are recommended for young infants and children with malnutrition, measles, or xerophthalmia, and the review recommends administering prophylactic vitamin A supplements to all infants under 59 months in countries at risk for insufficiency.  The review also suggests that lower doses of vitamin A, up to 10,000 IU daily, can safely be given to pregnant women with symptoms of vitamin A deficiency.

Although vitamin A deficiency is quite rare in developed countries, if you think you have a vitamin A deficiency, consider getting your blood levels tested.  As always, consult your doctor before you begin taking any vitamin or mineral supplement, to make sure your medications or health conditions don’t make it a serious risk.   

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References:

A Randomized, Placebo-Controlled, Clinical Trial of High-Dose Supplementation with Vitamins C and E, Beta Carotene, and Zinc for Age-Related Macular Degeneration and Vision Loss: AREDS Report No. 8. (2001). Arch Ophthalmology119(10), 1417–1436. doi: 10.1001/archopht.119.10/1417

Boyd, K., & Lipsky, S. N. (2020, January 16). What is Vitamin A Deficiency? Retrieved June 8, 2020, from https://www.aao.org/eye-health/diseases/vitamin-deficiency

Clagett-Dame, M., & Knutson, D. (2011). Vitamin A in Reproduction and Development. Nutrients3(4), 385–428. doi: 10.3390/nu3040385

Gilbert, C. (2013). What is Vitamin A and why do we need it? Community Eye Health26(84). Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3936685/

Graham-Maar, R. C. (2006). Elevated Vitamin A Intake and Serum Retinol in Preadolescent Children with Cystic Fibrosis. Am J Clin Nutr84(1), 174–182. doi: 10.1093/ajcn/84.1.174

Ross, D. A. (2002). Recommendations for Vitamin A Supplementation . The Journal of Nutrition 132(9), 2902S–2906S. doi: 10.1093/jn.132.9.2902S

The Effect of Vitamin E and Beta Carotene on the Incidence of Lung Cancer and Other Cancers in Male Smokers. (1994). N Engl J Med330(15), 1029–1035. doi: 10.1015/NEJM199404143301501

Vitamin A. (n.d.). Retrieved June 8, 2020, from https://www.hsph.harvard.edu/nutritionsource/vitamin-a/

Vitamin A and Skin Health. (2020, January 2). Retrieved June 9, 2020, from https://lpi.oregonstate.edu/mic/health-disease/skin-health/vitamin-A

Vitamin A: Fact Sheet for Health Professionals. (2020, February 14). Retrieved June 8, 2020, from https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/#en27

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