For example, the RDA of mcg RAE for adolescent and adult men is equivalent to 3, IU if the food or supplement source is preformed vitamin A retinol or if the supplement source is beta-carotene.
Therefore, a mixed diet containing mcg RAE provides between 3, and 36, IU vitamin A, depending on the foods consumed. Concentrations of preformed vitamin A are highest in liver and fish oils [ 2 ]. Other sources of preformed vitamin A are milk and eggs, which also include some provitamin A [ 2 ]. Most dietary provitamin A comes from leafy green vegetables, orange and yellow vegetables, tomato products, fruits, and some vegetable oils [ 2 ].
The top food sources of vitamin A in the U. Table 2 suggests many dietary sources of vitamin A. The foods from animal sources in Table 2 contain primarily preformed vitamin A, the plant-based foods have provitamin A, and the foods with a mixture of ingredients from animals and plants contain both preformed vitamin A and provitamin A. FDA developed DVs to help consumers compare the nutrient contents of foods and dietary supplements within the context of a total diet.
FDA does not require food labels to list vitamin A content unless vitamin A has been added to the food. The U. Department of Agriculture's USDA's FoodData Central [ 9 ] lists the nutrient content of many foods and provides a comprehensive list of foods containing vitamin A in IUs arranged by nutrient content and by food name , and foods containing beta-carotene in mcg arranged by nutrient content and by food name.
Vitamin A is available in multivitamins and as a stand-alone supplement, often in the form of retinyl acetate or retinyl palmitate [ 2 ]. A portion of the vitamin A in some supplements is in the form of beta-carotene and the remainder is preformed vitamin A; others contain only preformed vitamin A or only beta-carotene. Supplement labels usually indicate the percentage of each form of the vitamin. The amounts of vitamin A in stand-alone supplements range widely [ 2 ].
Multivitamin supplements typically contain —3, mcg RAE 2,—10, IU vitamin A, often in the form of both retinol and beta-carotene. Adults aged 71 years or older and children younger than 9 are more likely than members of other age groups to take supplements containing vitamin A. Although these intakes are lower than the RDAs for individual men and women, these intake levels are considered to be adequate for population groups. The adequacy of vitamin A intake decreases with age in children [ 4 ].
Furthermore, girls and African-American children have a higher risk of consuming less than two-thirds of the vitamin A RDA than other children [ 4 ]. Frank vitamin A deficiency is rare in the United States. However, vitamin A deficiency is common in many developing countries, often because residents have limited access to foods containing preformed vitamin A from animal-based food sources and they do not commonly consume available foods containing beta-carotene due to poverty [ 2 ].
According to the World Health Organization, million preschool-aged children and In these countries, low vitamin A intake is most strongly associated with health consequences during periods of high nutritional demand, such as during infancy, childhood, pregnancy, and lactation. In developing countries, vitamin A deficiency typically begins during infancy, when infants do not receive adequate supplies of colostrum or breast milk [ 12 ].
Chronic diarrhea also leads to excessive loss of vitamin A in young children, and vitamin A deficiency increases the risk of diarrhea [ 5 , 13 ]. The most common symptom of vitamin A deficiency in young children and pregnant women is xerophthalmia.
One of the early signs of xerophthalmia is night blindness, or the inability to see in low light or darkness [ 2 , 14 ].
Vitamin A deficiency is one of the top causes of preventable blindness in children [ 12 ]. People with vitamin A deficiency and, often, xerophthalmia with its characteristic Bitot's spots tend to have low iron status, which can lead to anemia [ 3 , 12 ]. Vitamin A deficiency also increases the severity and mortality risk of infections particularly diarrhea and measles even before the onset of xerophthalmia [ 5 , 12 , 14 ].
In developed countries, clinical vitamin A deficiency is rare in infants and occurs only in those with malabsorption disorders [ 15 ]. However, preterm infants do not have adequate liver stores of vitamin A at birth and their plasma concentrations of retinol often remain low throughout the first year of life [ 15 , 16 ]. Preterm infants with vitamin A deficiency have an increased risk of eye, chronic lung, and gastrointestinal diseases [ 15 ].
In developed countries, the amounts of vitamin A in breast milk are sufficient to meet infants' needs for the first 6 months of life.
But in women with vitamin A deficiency, breast milk volume and vitamin A content are suboptimal and not sufficient to maintain adequate vitamin A stores in infants who are exclusively breastfed [ 17 ]. The prevalence of vitamin A deficiency in developing countries begins to increase in young children just after they stop breastfeeding [ 3 ].
The most common and readily recognized symptom of vitamin A deficiency in infants and children is xerophthalmia. Pregnant women need extra vitamin A for fetal growth and tissue maintenance and for supporting their own metabolism [ 18 ]. The World Health Organization estimates that 9. Other effects of vitamin A deficiency in pregnant and lactating women include increased maternal and infant morbidity and mortality, increased anemia risk, and slower infant growth and development.
Most people with cystic fibrosis have pancreatic insufficiency, increasing their risk of vitamin A deficiency due to difficulty absorbing fat [ 19 , 20 ]. However, improved pancreatic replacement treatments, better nutrition, and caloric supplements have helped most patients with cystic fibrosis become vitamin A sufficient [ 21 ]. Several studies have shown that oral supplementation can correct low serum beta-carotene levels in people with cystic fibrosis, but no controlled studies have examined the effects of vitamin A supplementation on clinical outcomes in patients with cystic fibrosis [ ].
This section focuses on three diseases and disorders in which vitamin A might play a role: cancer, age-related macular degeneration AMD , and measles. Because of the role vitamin A plays in regulating cell growth and differentiation, several studies have examined the association between vitamin A and various types of cancer. However, the relationship between serum vitamin A levels or vitamin A supplementation and cancer risk is unclear.
Several prospective and retrospective observational studies in current and former smokers, as well as in people who have never smoked, found that higher intakes of carotenoids, fruits and vegetables, or both are associated with a lower risk of lung cancer [ 1 , 23 ]. In the Carotene and Retinol Efficacy Trial CARET , 18, current and former smokers including some males who had been occupationally exposed to asbestos took daily supplements containing 30 mg beta-carotene and 7, mcg RAE 25, IU retinyl palmitate for 4 years, on average [ 24 ].
In the beta-carotene component of the Physicians' Health Study, 22, male physicians took mg aspirin plus 50 mg beta-carotene, 50 mg beta-carotene plus aspirin placebo, mg aspirin plus beta-carotene placebo, or both placebos every other day for 12 years [ 26 ].
In all three of these studies, taking very high doses of beta-carotene, with or without 7, mcg RAE 25, IU retinyl palmitate or mg aspirin, did not prevent lung cancer. In fact, both the CARET and ATBC studies showed a significant increase in lung cancer risk among study participants taking beta-carotene supplements or beta-carotene and retinyl palmitate supplements.
The evidence on the relationship between beta-carotene and prostate cancer is mixed. Iron supplements: scientific issues concerning efficacy and implications for research and programs. Interactions between zinc and vitamin A: an update. Auld DS, Bergman T. Supplementation with vitamin A and iron for nutritional anaemia in pregnant women in West Java, Indonesia.
Kinetic analysis shows that iron deficiency decreases liver vitamin A mobilization in rats. Iron deficiency in young rats alters the distribution of vitamin A between plasma and liver and between hepatic retinol and retinyl esters. Tanumihardjo SA. Vitamin A: biomarkers of nutrition for development. Underwood BA, Arthur P.
The contribution of vitamin A to public health. Faseb J. Solomons NW. Present Knowledge in Nutrition. Epidemiology of vitamin A deficiency and xerophthalmia in at-risk populations. World Health Organization. Guideline - Vitamin A supplementation for infants and children months of age - Guideline. Geneva Guideline - Neonatal vitamin A supplementation Geneva Guideline - Vitamin A supplementation for infants 1—5 months of age - Guideline.
Gilbert C, Awan H. Blindness in children. Semba RD. Vitamin A and human immunodeficiency virus infection.
Proc Nutr Soc. Nutrients and their role in host resistance to infection. J Leukoc Biol. Vitamin A supplements: a guide to their use in the treatment and prevention of vitamin A deficiency and xerophthalmia. Geneva: World Health Organization ; Vitamin A deficiency is associated with gastrointestinal and respiratory morbidity in school-age children. Vitamin A supplementation for reducing the risk of mother-to-child transmission of HIV infection.
Cochrane Database Syst Rev. Maternal vitamin A deficiency and mother-to-child transmission of HIV Guideline - Vitamin A supplementation in pregnancy for reducing the risk of mother-to-child transmission of HIV. Effect of oral iodized oil on thyroid size and thyroid hormone metabolism in children with concurrent selenium and iodine deficiency. The effects of vitamin A deficiency and vitamin A supplementation on thyroid function in goitrous children.
J Clin Endocrinol Metab. Zimmermann MB. Interactions of vitamin A and iodine deficiencies: effects on the pituitary-thyroid axis.
Int J Vitam Nutr Res. Vitamin A supplementation in iodine-deficient African children decreases thyrotropin stimulation of the thyroid and reduces the goiter rate. Phrynoderma: a manifestation of vitamin A deficiency? The rest of the story. Pediatr Dermatol. An uncommon cause of esophagitis. Answer to the clinical challenges and images in GI question: image 1: esophageal hyperkeratosis secondary to vitamin A deficiency. Weber D, Grune T. The contribution of beta-carotene to vitamin A supply of humans.
Mol Nutr Food Res. Food and Nutrition Board, Institute of Medicine. Washington, D. National Academy Press. A trial of vitamin A therapy to facilitate ductal closure in premature infants. J Pediatr. Vitamin A supplementation for extremely-low-birth-weight infants.
N Engl J Med. Randomised controlled trial of oral vitamin A supplementation in preterm infants to prevent chronic lung disease. Survey of vitamin A supplementation for extremely-low-birth-weight infants: is clinical practice consistent with the evidence? Laughon MM. Vitamin A shortage and risk of bronchopulmonary dysplasia.
JAMA Pediatr. The effect of the national shortage of vitamin A on death or chronic lung disease in extremely low-birth-weight infants. Effects of early inhaled nitric oxide therapy and vitamin A supplementation on the risk for bronchopulmonary dysplasia in premature newborns with respiratory failure. Early postnatal additional high-dose oral vitamin A supplementation versus placebo for 28 days for preventing bronchopulmonary dysplasia or death in extremely low birth weight infants.
Babu TA, Sharmila V. Vitamin A supplementation in late pregnancy can decrease the incidence of bronchopulmonary dysplasia in newborns.
J Matern Fetal Neonatal Med. Vitamin A and carotenoids during pregnancy and maternal, neonatal and infant health outcomes: a systematic review and meta-analysis. Paediatr Perinat Epidemiol.
Impact of vitamin A supplementation on infant and childhood mortality. BMC Public Health. Gogia S, Sachdev HS. Vitamin A supplementation for the prevention of morbidity and mortality in infants six months of age or less.
High-dose vitamin A with vaccination after 6 months of age: a randomized trial. Non-specific effects of standard measles vaccine at 4. Interaction between neonatal vitamin A supplementation and timing of measles vaccination: a retrospective analysis of three randomized trials from Guinea-Bissau. Vitamin A for treating measles in children. Routine vitamin A supplementation for the prevention of blindness due to measles infection in children.
Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. The Beta-Carotene and Retinol Efficacy Trial: incidence of lung cancer and cardiovascular disease mortality during 6-year follow-up after stopping beta-carotene and retinol supplements.
J Natl Cancer Inst. Interplay of carotenoids with cigarette smoking: implications in lung cancer. Estimated intake of vitamin D and its interaction with vitamin A on lung cancer risk among smokers.
Int J Cancer. Drugs for preventing lung cancer in healthy people. Retinoic acid and arsenic trioxide for acute promyelocytic leukemia. Acitretin revisited in the era of biologics. J Dermatolog Treat. Oral retinoids in the treatment of seborrhoea and acne. Thielitz A, Gollnick H. Topical retinoids in acne vulgaris: update on efficacy and safety. Am J Clin Dermatol. Vishwanathan R, Johnson EJ. Eye disease. By continuing without changing your cookie settings, you agree to this collection.
For more information, please see our University Websites Privacy Notice. Many people take daily multivitamins to improve and maintain good health. Vitamin A, found in many dietary supplements, is known to support eye function, tissue growth, as well as bone, reproductive, and immune function.
What many people do not know is Vitamin A comes in many forms. The two main forms consumed by humans are retinol, found in animal sources of food, and beta carotene, an orange plant form. Richard Bailen. Rebecca Costello. Joseph M Betz. Karen Andrews. Pavel Gusev , Pavel Gusev. Pamela Pehrsson. Sushma Savarala. Phyuongtan Tey. James Harnly. Select Format Select format. Permissions Icon Permissions. Author disclosures: The authors report no conflicts of interest.
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