Dietary Supplement Fact Sheet:

Vitamin A

Introduction

See QuickFacts for easy-to-read facts about Vitamin A.

Vitamin A is the name of a group of fat-soluble retinoids, including retinol, retinal, retinoic acid, and retinyl esters [1-3]. Vitamin A is involved in immune function, vision, reproduction, and cellular communication [1,4,5]. Vitamin A is critical for vision as an essential component of rhodopsin, a protein that absorbs light in the retinal receptors, and because it supports the normal differentiation and functioning of the conjunctival membranes and cornea [2-4]. Vitamin A also supports cell growth and differentiation, playing a critical role in the normal formation and maintenance of the heart, lungs, kidneys, and other organs [2].

Two forms of vitamin A are available in the human diet: preformed vitamin A (retinol and its esterified form, retinyl ester) and provitamin A carotenoids [1-5]. Preformed vitamin A is found in foods from animal sources, including dairy products, fish, and meat (especially liver). By far the most important provitamin A carotenoid is beta-carotene; other provitamin A carotenoids are alpha-carotene and beta-cryptoxanthin. The body converts these plant pigments into vitamin A. Both provitamin A and preformed vitamin A must be metabolized intracellularly to retinal and retinoic acid, the active forms of vitamin A, to support the vitamin's important biological functions [2,3]. Other carotenoids found in food, such as lycopene, lutein, and zeaxanthin, are not converted into vitamin A.

The various forms of vitamin A are solubilized into micelles in the intestinal lumen and absorbed by duodenal mucosal cells [5]. Both retinyl esters and provitamin A carotenoids are converted to retinol, which is oxidized to retinal and then to retinoic acid [2]. Most of the body's vitamin A is stored in the liver in the form of retinyl esters.

Retinol and carotenoid levels are typically measured in plasma, and plasma retinol levels are useful for assessing vitamin A inadequacy. However, their value for assessing marginal vitamin A status is limited because they do not decline until vitamin A levels in the liver are almost depleted [3]. Liver vitamin A reserves can be measured indirectly through the relative dose-response test, in which plasma retinol levels are measured before and after the administration of a small amount of vitamin A [5]. A plasma retinol level increase of at least 20% indicates an inadequate vitamin A level [3,5,6]. For clinical practice purposes, plasma retinol levels alone are sufficient for documenting significant deficiency.

A plasma retinol concentration lower than 0.70 micromoles/L (or 20 micrograms [mcg]/dL) reflects vitamin A inadequacy in a population, and concentrations of 0.70–1.05 micromoles/L could be marginal in some people [5]. In some studies, high plasma or serum concentrations of some provitamin A carotenoids have been associated with a lower risk of various health outcomes, but these studies have not definitively demonstrated that this relationship is causal.

Recommended Intakes

Intake recommendations for vitamin A and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academies (formerly National Academy of Sciences) [5]. DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people. These values, which vary by age and gender, include:

Recommended Dietary Allowance (RDA): average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals.
Adequate Intake (AI): established when evidence is insufficient to develop an RDA and is set at a level assumed to ensure nutritional adequacy.
Estimated Average Requirement (EAR): average daily level of intake estimated to meet the requirements of 50% of healthy individuals. It is usually used to assess the adequacy of nutrient intakes in population groups but not individuals.
Tolerable Upper Intake Level (UL): maximum daily intake unlikely to cause adverse health effects.

RDAs for vitamin A are given as mcg of retinol activity equivalents (RAE) to account for the different bioactivities of retinol and provitamin A carotenoids (see Table 1). Because the body converts all dietary sources of vitamin A into retinol, 1 mcg of physiologically available retinol is equivalent to the following amounts from dietary sources: 1 mcg of retinol, 12 mcg of beta-carotene, and 24 mcg of alpha-carotene or beta-cryptoxanthin. From dietary supplements, the body converts 2 mcg of beta-carotene to 1 mcg of retinol.

Currently, vitamin A is listed on food and supplement labels in international units (IUs) even though nutrition scientists rarely use this measure. Conversion rates between mcg RAE and IU are as follows [7]:

1 IU retinol = 0.3 mcg RAE
1 IU beta-carotene from dietary supplements = 0.15 mcg RAE
1 IU beta-carotene from food = 0.05 mcg RAE
1 IU alpha-carotene or beta-cryptoxanthin = 0.025 mcg RAE

An RAE cannot be directly converted into an IU without knowing the source(s) of vitamin A. For example, the RDA of 900 mcg RAE for adolescent and adult men is equivalent to 3,000 IU if the food or supplement source is preformed vitamin A (retinol). However, this RDA is also equivalent to 6,000 IU of beta-carotene from supplements, 18,000 IU of beta-carotene from food, or 36,000 IU of alpha-carotene or beta-cryptoxanthin from food. So a mixed diet containing 900 mcg RAE provides between 3,000 and 36,000 IU of vitamin A, depending on the foods consumed.

Table 1: Recommended Dietary Allowances (RDAs) for Vitamin A [5]
Age	Male	Female	Pregnancy	Lactation
0–6 months*	400 mcg RAE	400 mcg RAE
7–12 months*	500 mcg RAE	500 mcg RAE
1–3 years	300 mcg RAE	300 mcg RAE
4–8 years	400 mcg RAE	400 mcg RAE
9–13 years	600 mcg RAE	600 mcg RAE
14–18 years	900 mcg RAE	700 mcg RAE	750 mcg RAE	1,200 mcg RAE
19–50 years	900 mcg RAE	700 mcg RAE	770 mcg RAE	1,300 mcg RAE
51+ years	900 mcg RAE	700 mcg RAE

* Adequate Intake (AI), equivalent to the mean intake of vitamin A in healthy, breastfed infants.

Sources of Vitamin A

Food

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.S. diet include dairy products, liver, fish, and fortified cereals; the top sources of provitamin A include carrots, broccoli, cantaloupe, and squash [4,5].

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.

Table 2: Selected Food Sources of Vitamin A [8]
Food	mcg RAE per serving	IU per serving	Percent DV*
Sweet potato, baked in skin, 1 whole	1,403	28,058	561
Beef liver, pan fried, 3 ounces	6,582	22,175	444
Spinach, frozen, boiled, ½ cup	573	11,458	229
Carrots, raw, ½ cup	459	9,189	184
Pumpkin pie, commercially prepared, 1 piece	488	3,743	249
Cantaloupe, raw, ½ cup	135	2,706	54
Peppers, sweet, red, raw, ½ cup	117	2,332	47
Mangos, raw, 1 whole	112	2,240	45
Black-eyed peas (cowpeas), boiled, 1 cup	66	1,305	26
Apricots, dried, sulfured, 10 halves	63	1,261	25
Broccoli, boiled, ½ cup	60	1,208	24
Ice cream, French vanilla, soft serve, 1 cup	278	1,014	20
Cheese, ricotta, part skim, 1 cup	263	945	19
Tomato juice, canned, ¾ cup	42	821	16
Herring, Atlantic, pickled, 3 ounces	219	731	15
Ready-to-eat cereal, fortified with 10% of the DV for vitamin A, ¾–1 cup (more heavily fortified cereals might provide more of the DV)	127–149	500	10
Milk, fat-free or skim, with added vitamin A and vitamin D, 1 cup	149	500	10
Baked beans, canned, plain or vegetarian, 1 cup	13	274	5
Egg, hard boiled, 1 large	75	260	5
Summer squash, all varieties, boiled, ½ cup	10	191	4
Salmon, sockeye, cooked, 3 ounces	59	176	4
Yogurt, plain, low fat, 1 cup	32	116	2
Pistachio nuts, dry roasted, 1 ounce	4	73	1
Tuna, light, canned in oil, drained solids, 3 ounces	20	65	1
Chicken, breast meat and skin, roasted, ½ breast	5	18	0

*DV = Daily Value. DVs were developed by the U.S. Food and Drug Administration (FDA) to help consumers compare the nutrient contents of products within the context of a total diet. The DV for vitamin A is 5,000 IU for adults and children age 4 and older. Foods providing 20% or more of the DV are considered to be high sources of a nutrient. The U.S. Department of Agriculture's (USDA's) Nutrient Database Web site [8] lists the nutrient content of many foods and provides a comprehensive list of foods containing vitamin A in IUs and foods containing beta-carotene in mcg.

Dietary supplements

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 2,500–10,000 IU vitamin A, often in the form of both retinol and beta-carotene.

About 28%–37% of the general population uses supplements containing vitamin A [9]. 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.

Vitamin A Intakes and Status

According to an analysis of data from the 2007–2008 National Health and Nutrition Examination Survey (NHANES), the average daily dietary vitamin A intake in Americans aged 2 years and older is 607 mcg RAE [10]. Adult men have slightly higher intakes (649 mcg RAE) than adult women (580 mcg RAE). Although these intakes are lower than the RDAs for individual men and women, these intake levels are considered to be adequate for population groups.

Data from NHANES III, conducted in 1988–1994, found that approximately 26% of the vitamin A in RAEs consumed by men and 34% of that consumed by women in the United States comes from provitamin A carotenoids, with the remainder coming from preformed vitamin A, mostly in the form of retinyl esters [5].

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].

Vitamin A Deficiency

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, 190 million preschool-aged children and 19.1 million pregnant women around the world have a serum retinol concentration below 0.70 micromoles/L [11]. 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 [11]. Chronic diarrhea also leads to excessive loss of vitamin A in young children, and vitamin A deficiency increases the risk of diarrhea [5,12]. 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 [2,13]. Vitamin A deficiency is one of the top causes of preventable blindness in children [11]. 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 [3,11]. Vitamin A deficiency also increases the severity and mortality risk of infections (particularly diarrhea and measles) even before the onset of xerophthalmia [5,11,13].

Groups at Risk of Vitamin A Inadequacy

The following groups are among those most likely to have inadequate intakes of vitamin A.

Premature Infants

In developed countries, clinical vitamin A deficiency is rare in infants and occurs only in those with malabsorption disorders [14]. 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 [14,15]. Preterm infants with vitamin A deficiency have an increased risk of eye, chronic lung, and gastrointestinal diseases [14].

Infants and Young Children in Developing Countries

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 [16]. 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 and Lactating Women in Developing Countries

Pregnant women need extra vitamin A for fetal growth and tissue maintenance and for supporting their own metabolism [17]. The World Health Organization estimates that 9.8 million pregnant women around the world have xerophthalmia as a result of vitamin A deficiency [11]. 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.

People with Cystic Fibrosis

Most people with cystic fibrosis have pancreatic insufficiency, increasing their risk of vitamin A deficiency due to difficulty absorbing fat [18,19]. Several cross-sectional studies found that 15%–40% of patients with cystic fibrosis have vitamin A deficiency [20]. However, improved pancreatic replacement treatments, better nutrition, and caloric supplements have helped most patients with cystic fibrosis become vitamin A sufficient [19]. 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 [19-21].

Vitamin A and Health

This section focuses on three diseases and disorders in which vitamin A might play a role: cancer, age-related macular degeneration (AMD), and measles.

Cancer

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 [1,22]. However, clinical trials have not shown that supplemental beta-carotene and/or vitamin A helps prevent lung cancer. In the Carotene and Retinol Efficacy Trial (CARET), 18,314 current and former smokers (including some males who had been occupationally exposed to asbestos) took daily supplements containing 30 mg beta-carotene and 25,000 IU retinyl palmitate for 4 years, on average [23]. In the Alpha-Tocopherol, Beta-Carotene (ATBC) Cancer Prevention Study, 29,133 male smokers took 50 mg/day alpha-tocopherol, 20 mg/day beta-carotene, 50 mg/day alpha-tocopherol and 20 mg/day beta-carotene, or placebo for 5–8 years [24]. In the beta-carotene component of the Physicians' Health Study, 22,071 male physicians took 325 mg aspirin plus 50 mg beta-carotene, 50 mg beta-carotene plus aspirin placebo, 325 mg aspirin plus beta-carotene placebo, or both placebos every other day for 12 years [25]. In all three of these studies, taking very high doses of beta-carotene, with or without 25,000 IU retinyl palmitate or 325 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 Physicians' Health Study did not find an increased lung cancer risk in participants taking beta-carotene supplements, possibly because only 11% of physicians in the study were current or former smokers.

The evidence on the relationship between beta-carotene and prostate cancer is mixed. CARET study participants who took daily supplements of beta-carotene and retinyl palmitate had a 35% lower risk of nonaggressive prostate cancer than men not taking the supplements [26]. However, the ATBC study found that baseline serum beta-carotene and retinol levels and supplemental beta-carotene had no effect on survival [27]. Moreover, men in the highest quintile of baseline serum retinol levels were 20% more likely to develop prostate cancer than men in the lowest quintile [28].

The ATBC and CARET study results suggest that large supplemental doses of beta-carotene with or without retinyl palmitate have detrimental effects in current or former smokers and workers exposed to asbestos. The relevance of these results to people who have never smoked or to the effects of beta-carotene or retinol from food or multivitamins (which typically have modest amounts of beta-carotene) is not known. More research is needed to determine the effects of vitamin A on prostate, lung, and other types of cancer.

Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a major cause of significant vision loss in older people. AMD's etiology is usually unknown, but the cumulative effect of oxidative stress is postulated to play a role. If so, supplements containing carotenoids with antioxidant functions, such as beta-carotene, lutein, and zeaxanthin, might be useful for preventing or treating this condition. Lutein and zeaxanthin, in particular, accumulate in the retina, the tissue in the eye that is damaged by AMD.

The Age-Related Eye Disease Study (AREDS), a large randomized clinical trial, found that participants with some degree of AMD reduced their risk of developing advanced AMD by 25% by taking a daily supplement containing beta-carotene (15 mg), vitamin E (400 IU dl-alpha-tocopheryl acetate), vitamin C (500 mg), zinc (80 mg), and copper (2 mg) for 5 years compared to participants taking a placebo [29].

A follow-up AREDS2 study confirmed the value of this supplement in reducing the progression of AMD over a median follow-up period of 5 years but found that adding lutein (10 mg) and zeaxanthin (2 mg) or omega-3 fatty acids to the formulation did not confer any additional benefits [30]. Importantly, the study revealed that beta-carotene was not a required ingredient; the original AREDS formulation without beta-carotene provided the same protective effect against developing advanced AMD. In a more detailed analysis of results, supplementation with lutein and zeaxanthin reduced the risk of advanced AMD by 26% in participants with the lowest dietary intakes of these two carotenoids who took a supplement containing them compared to those who did not take a supplement with these carotenoids [30]. The risk of advanced AMD was also 18% lower in participants who took the modified AREDS supplement containing lutein and zeaxanthin but not beta-carotene than in participants who took the formulation with beta-carotene but not lutein or zeaxanthin.

Individuals who have or are developing AMD should talk to their health care provider about taking one of the supplement formulations used in AREDS.

Measles

Measles is a major cause of morbidity and mortality in children in developing countries. About half of all measles deaths happen in Africa, but the disease is not limited to low-income countries. Vitamin A deficiency is a known risk factor for severe measles. The World Health Organization recommends high oral doses (200,000 IU) of vitamin A for two days for children over age 1 with measles who live in areas with a high prevalence of vitamin A deficiency [31].

A Cochrane review of eight randomized controlled trials of treatment with vitamin A for children with measles found that 200,000 IU of vitamin A on each of two consecutive days reduced mortality from measles in children younger than 2 and mortality due to pneumonia in children [31]. Vitamin A also reduced the incidence of croup but not pneumonia or diarrhea, although the mean duration of fever, pneumonia, and diarrhea was shorter in children who received vitamin A supplements. A meta-analysis of six high-quality randomized controlled trials of measles treatment also found that two doses of 100,000 IU in infants and 200,000 IU in older children significantly reduced measles mortality [32]. The vitamin A doses used in these studies are much higher than the UL. The effectiveness of vitamin A supplementation to treat measles in countries, such as the United States, where vitamin A intakes are usually adequate is uncertain.

The body needs vitamin A to maintain the corneas and other epithelial surfaces, so the lower serum concentrations of vitamin A associated with measles, especially in people with protein-calorie malnutrition, can lead to blindness. None of the studies evaluated in a Cochrane review evaluated blindness as a primary outcome [33]. However, a careful clinical investigation of 130 African children with measles revealed that half of all corneal ulcers in these children, and nearly all bilateral blindness, occurred in those with vitamin A deficiency [34].

Health Risks from Excessive Vitamin A

Because vitamin A is fat soluble, the body stores excess amounts, primarily in the liver, and these levels can accumulate. Although excess preformed vitamin A can have significant toxicity (known as hypervitaminosis A), large amounts of beta-carotene and other provitamin A carotenoids are not associated with major adverse effects [35]. The manifestations of hypervitaminosis A depend on the size and rapidity of the excess intake. The symptoms of hypervitaminosis A following sudden, massive intakes of vitamin A, as with Arctic explorers who ate polar bear liver, are acute [36]. Chronic intakes of excess vitamin A lead to increased intracranial pressure (pseudotumor cerebri), dizziness, nausea, headaches, skin irritation, pain in joints and bones, coma, and even death [2,4,5]. Although hypervitaminosis A can be due to excessive dietary intakes, the condition is usually a result of consuming too much preformed vitamin A from supplements or therapeutic retinoids [3,5]. When people consume too much vitamin A, their tissue levels take a long time to fall after they discontinue their intake, and the resulting liver damage is not always reversible.

Observational studies have suggested an association between high intakes of preformed vitamin A (more than 1,500 mcg daily—only slightly higher than the RDA), reduced bone mineral density, and increased fracture risk [1,4,37]. However, the results of studies on this risk have been mixed, so the safe retinol intake level for this association is unknown.

Total intakes of preformed vitamin A that exceed the UL and some synthetic retinoids used as topical therapies (such as isotretinoin and etretinate) can cause congenital birth defects [2-4]. These birth defects can include malformations of the eye, skull, lungs, and heart [4]. Women who might be pregnant should not take high doses of vitamin A supplements [2].

Unlike preformed vitamin A, beta-carotene is not known to be teratogenic or lead to reproductive toxicity [1]. And even large supplemental doses (20–30 mg/day) of beta-carotene or diets with high levels of carotenoid-rich food for long periods are not associated with toxicity. The most significant effect of long-term, excess beta-carotene is carotenodermia, a harmless condition in which the skin becomes yellow-orange [1,22]. This condition can be reversed by discontinuing beta-carotene ingestion.

Supplementation with beta-carotene, with or without retinyl palmitate, for 5–8 years has been associated with an increased risk of lung cancer and cardiovascular disease in current and former male and female smokers and in male current and former smokers occupationally exposed to asbestos [24,38]. In the ATBC study, beta-carotene supplements (20 mg daily) were also associated with increased mortality, mainly due to lung cancer and ischemic heart disease [24]. The CARET study ended early, after the investigators found that daily beta-carotene (30 mg) and retinyl palmitate (25,000 IU) supplements increased the risk of lung cancer and cardiovascular disease mortality [38].

The FNB has established ULs for preformed vitamin A that apply to both food and supplement intakes [5]. The FNB based these ULs on the amounts associated with an increased risk of liver abnormalities in men and women, teratogenic effects, and a range of toxic effects in infants and children. The FNB also considered levels of preformed vitamin A associated with decreased bone mineral density, but did not use these data as the basis for its ULs because the evidence was conflicting. The FNB has not established ULs for beta-carotene and other provitamin A carotenoids [22]. The FNB advises against beta-carotene supplements for the general population, except as a provitamin A source to prevent vitamin A deficiency.

Table 3: Tolerable Upper Intake Levels (ULs) for Preformed Vitamin A [5]*
Age	Male	Female	Pregnancy	Lactation
0–12 months	600 mcg RAE (2,000 IU)	600 mcg RAE (2,000 IU)
1–3 years	600 mcg RAE (2,000 IU)	600 mcg RAE (2,000 IU)
4–8 years	900 mcg RAE (3,000 IU)	900 mcg RAE (3,000 IU)
9–13 years	1,700 mcg RAE (5,667 IU)	1,700 mcg RAE (5,667 IU)
14–18 years	2,800 mcg RAE (9,333 IU)	2,800 mcg RAE (9,333 IU)	2,800 mcg RAE (9,333 IU)	2,800 mcg RAE (9,333 IU)
19+ years	3,000 mcg RAE (10,000 IU)	3,000 mcg RAE (10,000 IU)	3,000 mcg RAE (10,000 IU)	3,000 mcg RAE (10,000 IU)

* These ULs, expressed in mcg and in IUs (where 1 mcg = 3.33 IU), only apply to products from animal sources and supplements whose vitamin A comes entirely from retinol or ester forms, such as retinyl palmitate. However, many dietary supplements (such as multivitamins) do not provide all of their vitamin A as retinol or its ester forms. For example, the vitamin A in some supplements consists partly or entirely of beta-carotene or other provitamin A carotenoids. In such cases, the percentage of retinol or retinyl ester in the supplement should be used to determine whether an individual's vitamin A intake exceeds the UL. For example, a supplement labeled as containing 10,000 IU of vitamin A with 60% from beta-carotene (and therefore 40% from retinol or retinyl ester) provides 4,000 IU of preformed vitamin A. That amount is above the UL for children from birth to 13 years but below the UL for adolescents and adults.

Interactions with Medications

Vitamin A can interact with certain medications, and some medications can have an adverse effect on vitamin A levels. A few examples are provided below. Individuals taking these and other medications on a regular basis should discuss their vitamin A status with their health care providers.

Orlistat

Orlistat (Alli®, Xenical®), a weight-loss treatment, can decrease the absorption of vitamin A, other fat-soluble vitamins, and beta-carotene, causing low plasma levels in some patients [39]. The manufacturers of Alli and Xenical recommend encouraging patients on orlistat to take a multivitamin supplement containing vitamin A and beta-carotene, as well as other fat-soluble vitamins [40,41].

Retinoids

Several synthetic retinoids derived from vitamin A are used orally as prescription medicines. Examples include the psoriasis treatment acitretin (Soriatane®) and bexarotene (Targretin®), used to treat the skin effects of T-cell lymphoma. Retinoids can increase the risk of hypervitaminosis A when taken in combination with vitamin A supplements [39].

Vitamin A and Healthful Diets

The federal government's 2010 Dietary Guidelines for Americans notes that "nutrients should come primarily from foods. Foods in nutrient-dense, mostly intact forms contain not only the essential vitamins and minerals that are often contained in nutrient supplements, but also dietary fiber and other naturally occurring substances that may have positive health effects. ...Dietary supplements...may be advantageous in specific situations to increase intake of a specific vitamin or mineral."

The Dietary Guidelines for Americans describes a healthy diet as one that:

Emphasizes a variety of fruits, vegetables, whole grains, and fat-free or low-fat milk and milk products.
Many fruits, vegetables, and dairy products are good sources of vitamin A. Some ready-to-eat breakfast cereals are fortified with vitamin A.
Includes lean meats, poultry, seafood, beans and peas, eggs, and nuts and seeds.
Beef liver contains high amounts of vitamin A. Other sources of the nutrient include some fish, beans, and nuts.
Limits solid fats (saturated fats and trans fats), cholesterol, salt (sodium), added sugars, and refined grains.
Stays within your calorie needs.

For more information about building a healthful diet, refer to the Dietary Guidelines for Americans and the U.S. Department of Agriculture's food guidance system, MyPlate.

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Borowitz D, Baker RD, Stallings V. Consensus report on nutrition for pediatric patients with cystic fibrosis. J Pediatr Gastroenterol Nutr 2002;35:246-59.
Michel SH, Maqbool A, Hanna MD, Mascarenhas M. Nutrition management of pediatric patients who have cystic fibrosis. Pediatr Clin North Am 2009;56:1123-41. [PubMed abstract]
Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids . Washington, DC: National Academy Press; 2000.
Omenn GS, Goodman GE, Thornquist MD, Balmes J, Cullen MR, Glass A, et al. Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. N Engl J Med 1996;334:1150-5. [PubMed abstract]
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Hennekens CH, Buring JE, Manson JE, Stampfer M, Rosner B, Cook NR, et al. Lack of effect of long-term supplementation with beta carotene on the incidence of malignant neoplasms and cardiovascular disease. The New England journal of medicine 1996;334:1145-9. [PubMed abstract]
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Disclaimer

This fact sheet by the Office of Dietary Supplements provides information that should not take the place of medical advice. We encourage you to talk to your health care providers (doctor, registered dietitian, pharmacist, etc.) about your interest in, questions about, or use of dietary supplements and what may be best for your overall health. Any mention in this publication of a specific brand name is not an endorsement of the product.

Glossary

absorption: In nutrition, the process of moving protein, carbohydrates, fats, and other nutrients from the digestive system into the bloodstream. Most absorption occurs in the small intestine.
acne: A sometimes severe skin condition that commonly occurs on the face, neck, back, and chest and includes whiteheads, blackheads, and pimples. Severe acne may be painful and can leave permanent deep scars.
Adequate Intake: AI. The recommended daily intake of a nutrient estimated by the Institute of Medicine to meet or exceed the amount needed to maintain adequate nutrition for most people in a particular life stage and gender group. An AI is established when not enough information is available from scientific research to determine a Recommended Dietary Allowance (a dietary intake level that is sufficient to meet the nutrient requirements of most people).
administration: The process of giving a person a medicine or dietary supplement by mouth, by vein, on the skin, or by another route. For example, a 14-day administration of valerian extract.
adverse effect: An unwanted side effect.
adverse response: An unwanted or harmful reaction to treatment.
alpha-carotene: A substance found in colorful fruits and vegetables such as pumpkin, carrots, winter squash, and tangerines. It is a carotenoid that can be made into vitamin A by the body.
American Academy of Pediatrics: AAP. An organization of pediatricians (medical doctors who specialize in the development, care, and diseases of children) that works to improve the health and well-being of infants, children, adolescents, and young adults.
amino acid: A chemical building block of protein.
antioxidant: A substance that protects cells from damage caused by free radicals (compounds formed during the metabolism of oxygen). It may help prevent the development of some chronic diseases such as cancer. Antioxidants include beta-carotene; lutein; lycopene; vitamins A, C, and E; selenium; and zinc.
association: A relationship between two conditions or states such that if one is present, the other is likely to be present as well. An association between two conditions or states, however, does not necessarily imply a cause and effect relationship. The terms association and relationship are often used interchangeably.
bacteria: Single-celled organisms that are too small to be seen without a microscope. Bacteria are found everywhere and may be helpful or harmful.
beta-carotene: A carotenoid found in carrots, cantaloupe, apricots, sweet potatoes, pumpkin, winter squash, mangos, collard greens, spinach, kale, broccoli, and other orange, red, and dark green fruits and vegetables.
beta-cryptoxanthin: A substance found in citrus fruit, peaches, and apricots. It is an antioxidant. Beta-cryptoxanthin is one of a group of carotenoids that can be made into vitamin A in the body.
biological activity: An effect on life processes. For example, the biological activity of a vitamin means the effect it has on specific life processes in the body.
body stores: The amount of a nutrient that stays in the body after eating and is available for future use. The size and location of this extra supply differs depending on the nutrient. For example, iron is stored in the liver.
bone density: A measurement of bone mass and an indicator of bone strength and health. Also called bone mineral density.
calcium: A mineral found throughout the body. Calcium is needed for healthy bones and teeth, for nerves and enzymes to function properly, and for blood clotting. Calcium is found in some foods, including milk, yogurt, and cheese, and in Chinese cabbage, kale, broccoli and fortified foods, such as many drinks, tofu, and cereals.
carotenoid: A substance that makes certain fruits and vegetables yellow, orange, or red. Some carotenoids (beta-carotene, alpha-carotene, and beta-cryptoxanthin) can be made into vitamin A by the body. Other carotenoids (lycopene, lutein, and zeaxanthin) cannot be made into vitamin A by the body. All carotenoids are antioxidants.
celiac disease: An autoimmune disorder in which eating gluten (a protein found in wheat, rye, barley, and possibly oats) causes the immune system to damage the small intestine, making it unable to absorb nutrients. It is a genetic disease that sometimes becomes active for the first time after surgery, pregnancy, childbirth, viral infection, or extreme stress. Also called sprue.
cell: The individual unit that makes up the tissues of the body. All living things are made up of one or more cells, which are the smallest units of living structure capable of independent existence.
cell differentiation: The process during which young, immature (unspecialized) cells take on individual characteristics and reach their mature (specialized) form and function. For example, unspecialized cells differentiate to become nerve cells, muscle cells, blood cells, or other specialized tissue cells.
cell division: The method by which a single cell divides to create two cells. This is a continuous process that allows a population of cells to increase in number or remain the same in number.
Centers for Disease Control and Prevention: CDC. An organization within the federal government responsible for prevention and control of infectious disease and other health threats. It is part of the US Department of Health and Human Services.
central nervous system disorder: A disease or condition that affects the brain, the spinal cord, and the ability to think, move, see, hear, taste, smell, or touch.
chemoprevention: The use of drugs, vitamins, or other substances to try to reduce the risk of, or delay the development or recurrence of, cancer.
chronic disease: A condition that is continuous or recurrent, is not easily cured, and cannot be passed from person to person. Examples of chronic diseases include heart disease, diabetes, and asthma.
clinical trial: A type of research study that uses volunteers to test the safety and efficacy (the ability to produce a beneficial effect) of new methods of screening (checking for disease when there are no symptoms), prevention, diagnosis, or treatment of a disease. Also called a clinical study.
complication: In medicine, an illness or condition that occurs while a patient has a disease. The complication is not a part of the disease, but may be a result of the disease or may be unrelated.
compound: In pharmacy, a substance that contains more than one ingredient.
control: In a clinical trial, the group of participants that does not receive the new treatment being studied. This group is compared with the group receiving the new treatment, to see whether the new treatment works. In an observational study, the controls are participants who do not have a particular health condition; the control group is compared with the group of participants who do have the condition to see if certain factors (such as diet, activity level, or use of dietary supplements) may be associated with developing or preventing the condition.
cornea: The clear dome-shaped surface covering the front of the eye.
Crohn's disease: A long-lasting (chronic) disease that causes severe irritation in the gastrointestinal tract. It usually affects the lower small intestine (called the ileum) or the colon, but it can affect any part of the digestive tract from the mouth to the anus. It is painful, causing severe watery or bloody diarrhea, and may lead to life-threatening complications. Crohn's disease is a form of inflammatory bowel disease.
cure: To heal or restore health; a treatment to restore health.
Daily Value: DV. A term used on a food or dietary supplement label that tells you how much of a particular nutrient (such as calcium) one serving of the food or supplement provides. DVs are given as percentages and help you compare one product with another. For example, a food that lists 40% DV for calcium would provide much more calcium than another food that lists 10% DV for calcium. For each nutrient, there is one DV for all people aged 4 years and older. DVs are established by the U.S. Food and Drug Administration.
dairy food: Milk and products made with milk, such as buttermilk, yogurt, cheese, cottage cheese, and ice cream.
deciliter: dL. A unit of volume in the metric system equal to one-tenth of a liter (about two-tenths of a pint).
deficiency: An amount that is not enough; a shortage.
diagnose: The process of using signs and symptoms to identify a disease.
diarrhea: Loose, watery stools.
diarrheal infection: A disease in which viruses, bacteria, or parasites invade the body and multiply, causing abdominal pain, cramping, and frequent watery bowel movements.
Dietary Guidelines for Americans: Advice from the federal government to promote health and reduce the chance (risk) of long-lasting (chronic) diseases through nutrition and physical activity. The Guidelines are updated and published every 5 years by the US Department of Health and Human Services and the US Department of Agriculture.
Dietary Reference Intake: DRI. A term developed by the Institute of Medicine that refers to a set of recommendations used to plan and evaluate the nutrient intake of healthy people. The DRIs include the Estimated Average Requirement (an intake value estimated to meet the nutrient requirements of half of all people), the Recommended Dietary Allowance (a dietary intake level that is sufficient to meet the nutrient requirements of most people), Adequate Intake (a recommended nutrient intake that meets or exceeds the amount needed to maintain adequate nutrition in most people), and the Tolerable Upper Intake Level (the largest daily intake of a nutrient that is considered unlikely to cause harmful side effects for most people).
dietary supplement: A product that is intended to supplement the diet. A dietary supplement contains one or more dietary ingredients (including vitamins, minerals, herbs or other botanicals, amino acids, and other substances) or their components; is intended to be taken by mouth as a pill, capsule, tablet, or liquid; and is identified on the front label of the product as being a dietary supplement.
digestion: The process the body uses to break down food into simple substances for energy, growth, and cell repair.
dose: The amount of medicine or other substance taken at one time or over a specific period of time.
enzyme: A protein that speeds up chemical reactions in the body.
epidemiologic study: Research that examines the patterns, causes, and control of a disease in a population of people.
esophageal cancer: Uncontrolled growth of abnormal cells in the esophagus (the hollow muscular tube that moves food and liquid from the throat to the stomach). Cancer starts in the mucous membrane lining the inside of the esophagus and spreads outward through the layers of connective tissue and muscle as it grows.
estrogen: A hormone (a chemical made by the body that controls the actions of certain cells or organs) that is needed to develop and maintain female sex characteristics and the growth of long bones. Estrogens are also made in the laboratory and are used in birth control and to treat symptoms of menopause, menstrual disorders, and osteoporosis.
evidence: Information used to support the use of a particular screening procedure, treatment, or preventive measure. In medicine, evidence needed to determine effectiveness is provided by laboratory research, clinical trials, and other studies.
fortify: To add nutrients to a food during processing or to replace nutrients lost when a food product is produced or stored. This process is sometimes called enrichment. For example, when calcium is added to processed orange juice, the orange juice is said to be "fortified with calcium." Another example is adding folic acid to flour.
fracture: A break, for example, a bone fracture.
free radical: An atom or molecule made in the body that can damage cells. A free radical has at least one unpaired electron, which makes it unstable. To become stable, the free radical takes an electron away from another atom, which makes that atom unstable, and starts a chain reaction that can injure cells. Free radicals are made during chemical changes that take place in a cell or an organism to produce energy and basic materials needed for important life processes (metabolism). They also come from tobacco smoke, pollution, radiation from the sun and x-rays, and other sources outside the body. Free radicals damage cells, cause genetic alterations (mutations), and may play a role in cancer, heart disease, and age-related diseases (such as Alzheimerâ€™s, Parkinsonâ€™s, and Lou Gehrigâ€™s diseases). Free radicals are also beneficial; they are involved in killing germs (microorganisms) and they help hormones and chemical messengers communicate with cells. Proteins (enzymes) made by the body, and vitamin C, vitamin E, and beta carotene in the diet help prevent free radical damage.
gastric cancer: Uncontrolled growth of abnormal cells in the stomach that spreads through the outer layers of the stomach as it grows.
gastrointestinal motility disorder: A condition in which digestion (the process in which food is moved through the gastrointestinal tract by repeating contractions called peristalsis) is abnormal because peristalsis does not work properly. It may be caused by problems with the muscles or nerves in the intestine, or by a problem with the hormones that tell the intestines when to contract. Gastrointestinal motility disorder may cause peristalsis to stop or be too fast or too slow, which causes bloating, constipation, diarrhea, difficulty swallowing, gas, heartburn, nausea, or vomiting. It may be the result of a genetic disorder, a disease (such as diabetes), or no known cause. Examples of gastrointestinal motility disorder include irritable bowel syndrome and gastroesophageal reflux disease.
genetic disorder: A disease or disorder caused by an alteration or variation (mutation) in a gene or group of genes in the cells of an individual. Examples of genetic disorders include breast cancer, cystic fibrosis, Parkinson's disease, and celiac disease. They can be inherited or can occur without a known cause.
genetics: Heredity passed from parent to offspring. Also, the identification and study of genes within an organism, their function in normal development, the consequences of gene alteration or variation (mutation), and potential treatments for genetic diseases.
gluten: A protein found in wheat, rye, and barley. Eating gluten damages the small intestine in people who have celiac disease (also called gluten intolerance, gluten-sensitive enteropathy, and sprue) and can cause abdominal pain, gas, diarrhea, and other symptoms.
hormone: A group of chemicals made by glands in the body. Hormones circulate in the bloodstream and control the actions of certain cells or organs. Some hormones can also be manufactured.
hypervitaminosis A: Abnormally high amounts of vitamin A stored in the body. It can cause headache, blurred vision, nausea, vomiting, dizziness, and birth defects. Also called vitamin A toxicity.
immune system: A group of organs and cells that defends the body against infection, disease, and altered (mutated) cells. It includes the thymus, spleen, lymphatic system (lymph nodes and lymph vessels), bone marrow, tonsils, and white blood cells.
immunization: A method used to cause an immune response that helps protect against a specific disease, especially an infectious one. An example is the injection given to prevent chicken pox.
in vitro: In the laboratory (outside the body).
incidence: The number of new cases of a disease diagnosed in a specific group of people during a specific period of time. For example, the annual incidence of childhood cancer is 14.6 cases per 100,000 children aged birth to 14 years.
infant: A child younger than 12 months old.
infection: The invasion and spread of germs in the body. The germs may be bacteria, viruses, yeast, or fungi.
inflammatory bowel disease: IBD. Long-lasting (chronic) problems that cause irritation and ulcers in the digestive tract. The most common disorders are ulcerative colitis and Crohn's disease.
Institute of Medicine: IOM. A private nongovernmental organization that issues reports on biomedical science, medicine, and health as requested by government agencies, private industry, and foundations.
International Unit: IU. A measurement used to measure the activity of some vitamins and other biological substances (such as enzymes and hormones).
intestine: The section of the digestive tract below the stomach, including the small and large intestines, rectum, and anus.
iron: In nutrition, a mineral the body needs to make red blood cells, proteins, and enzymes; and for the control of cell growth and cell specialization. Iron is found in some foods, including red meats, fish, poultry, lentils, and beans.
isotretinoin: A form of vitamin A used as a drug (such as Accutane) to treat acne and psoriasis. It is being studied in the prevention of some types of cancer. It can cause birth defects and may interfere with the ability of the liver to function properly. Also called 13-cis retinoic acid.
label: When referring to dietary supplements, information that appears on the product container, including a descriptive name of the product stating that it is a "supplement"; the name and place of business of the manufacturer, packer, or distributor; a complete list of ingredients; and each dietary ingredient contained in the product. Supplements must also include directions for use, nutrition labeling in the form of a Supplement Facts panel that identifies each dietary ingredient contained in the product and the serving size, amount, and active ingredients.
laboratory study: Research done in a laboratory. A laboratory study may use cells in test tubes or animals to find out if a drug, procedure, or other treatment is likely to be safe and useful. Laboratory studies usually take place before any testing is done in humans.
liver: A large organ located in the right upper abdomen. It stores nutrients that come from food, makes chemicals needed by the body, and breaks down some medicines and harmful substances so they can be removed from the body.
lutein: A substance found in egg yolk and colorful fruits and vegetables such as spinach, kale, collard greens, broccoli, peas, brussels sprouts, kiwi, and red seedless grapes. Lutein is a carotenoid the body cannot use to make vitamin A. It is being studied in the prevention of certain eye diseases (age-related macular degeneration and cataracts).
lycopene: A substance found in tomato products. Lycopene is also found in some colorful fruits and vegetables such as watermelon, guava, papaya, apricots, pink grapefruit, and blood oranges. Lycopene is a carotenoid the body cannot use to make vitamin A. It is being studied in the prevention of some types of cancer.
lymphocyte: A type of white blood cell that is part of the immune system. It defends the body against infection, disease, and altered (mutated) cells.
malabsorption: A reduced ability to properly absorb nutrients. It can be caused by injury to the digestive tract, a genetic disease, or other conditions. Malabsorption can lead to malnutrition.
malnutrition: A disorder caused by a diet that does not provide enough nutrition, an unbalanced diet, a digestive system that does not work properly, or a problem with absorbing or using nutrients.
measles: A group of diseases of the respiratory tract caused by a virus. Measles is highly contagious and spreads easily from person to person through coughing or sneezing. Symptoms include fever, cough, red and irritated eyes, and a spreading rash. Serious complications include pneumonia, inflammation of the brain, and death. One form called German measles may cause births defects in a fetus if a woman is infected early in her pregnancy.
metabolism: All chemical changes that take place in a cell or an organism. These changes produce energy and basic materials needed for important life processes.
microgram: µg or mcg. A unit of weight in the metric system equal to one millionth of a gram. (A gram is approximately one-thirtieth of an ounce.)
microorganism: A living being that can be seen only through a microscope. Microorganisms include helpful and harmful bacteria, protozoa, algae, and fungi. Although viruses are not considered living organisms, they are sometimes classified as microorganisms.
milligram: mg. A measure of weight. It is a metric unit of mass equal to 0.001 gram (it weighs 28,000 times less than an ounce).
mucous membrane: The moist tissue that lines some organs and body cavities (such as the nose, mouth, and lungs) and makes mucus (a thick, slippery fluid). Also called mucosa.
Nurses' Health Study: An ongoing long-term study of diet, nutrition, and risk factors for major chronic disease in a large number of women in the United States.
nutrient: A chemical compound in food that is used by the body to function and maintain health. Examples of nutrients include proteins, fats, carbohydrates, vitamins, and minerals.
nutritional: Having to do with nutrition (eating, digesting, and absorbing the nutrients in food, and the health and disease consequences).
osteoporosis: A condition in which bones become weak and brittle, increasing the chance they may break.
pancreas: An organ in the abdomen. It makes a liquid (called pancreatic juice) containing enzymes that aid in digestion, and makes several hormones, including insulin. The pancreas is surrounded by the stomach and intestines.
percentile: A ranking on a scale of 100 that indicates the percent of others at or below that score. For example, a child with a weight in the 95th percentile for her age is heavier than 95 percent of all children her age; 5 percent of children her age weigh more.
Physicians' Health Study: One of two long-term studies conducted to see whether the long-term use of aspirin or various nutritional supplements such as beta-carotene, vitamins C and E, and multivitamins can prevent heart disease, cancer, and age-related eye diseases in men in the United States.
placebo: An inactive substance or treatment that has no effect on the body and that ideally looks, smells, and tastes the same as, and is given the same way as, the active drug or treatment being tested. The effects of the active substance or treatment are compared to the effects of the placebo.
pneumonia: Inflammation of one or both lungs. Bacteria, viruses, fungi, parasites, other germs, and injury can cause the lungs to become inflamed and fill with fluid. Symptoms can appear suddenly, range from mild to severe, and may include fever, chills, chest pain, cough, shortness of breath, and difficult breathing. Anyone can develop pneumonia, but it is especially dangerous in babies, older people, and people with weakened immune systems, lung disease, heart disease, or diabetes.
porous: Full of holes.
postmenopausal: Having to do with the time after menopause. The time in a woman's life when menstrual periods stop permanently is called menopause ("change of life").
prescription: A written order from a health care provider for medicine, therapy, or tests.
prevent: To stop from happening.
prevention: In medicine, action taken to decrease the chance (risk) of developing a disease.
protein: A molecule made up of amino acids that the body needs for good health. Proteins are the basis of body structures such as skin and muscle, and substances such as enzymes and antibodies.
protein-energy malnutrition: A group of conditions that result when the body does not get enough protein or energy (calories), or both, to support growth and development and for the body to work properly.
provitamin: A substance found in some foods that the body can use to make a vitamin. An example of a provitamin is beta-carotene, which the body uses to make vitamin A. Also called a vitamin precursor.
psoriasis: A chronic inflammatory disease in which the skin becomes swollen, red, and itchy, with patches of silvery-white scales.
randomization: When referring to an experiment or clinical trial, the process by which animal or human subjects are assigned by chance to separate groups that compare different treatments or other therapies. Randomization gives each participant an equal chance of being assigned to any of the groups.
Recommended Dietary Allowance: RDA. The average amount of a nutrient a healthy person should get each day. RDAs vary by age, gender and whether a woman is pregnant or breastfeeding. For example, the RDA for vitamin C is 80 mg a day for a pregnant teenager and 90 mg a day for men. RDAs are developed by the Food and Nutrition Board at the Institute of Medicine of the National Academies.
respiratory: Having to do with breathing. The organs that are involved with breathing include the mouth, nose, throat (pharynx), voicebox (larynx), windpipe (trachea), air passages between the windpipe and lungs (bronchial tubes), and lungs.
respiratory tract: The organs that are involved in breathing. These include the mouth, nose, throat (pharynx), voicebox (larynx), windpipe (trachea), air passages between the windpipe and lungs (bronchial tubes), and lungs. Also called the respiratory system.
retina: The light-sensitive layers of nerve tissue at the back of the eye that receive images and send them as electric signals through the optic nerve to the brain.
retinal: The form of vitamin A needed for proper vision. It is made by the body from beta-carotene. Also called retinaldehyde.
retinitis pigmentosa: A group of inherited eye diseases that affect the retina (the light-sensitive part of the eye), causing a gradual loss of night vision and peripheral vision and usually resulting in partial blindness.
retinoid: A category of vitamin A compounds. The retinoids include retinol, retinal, and retinoic acid. Synthetic retinoids are manufactured for use in treating acne, psoriasis, and other skin disorders.
retinol: A form of vitamin A found only in foods that come from animals. The body can use retinol to make retinal and retinoic acid (other forms of vitamin A). Retinol is found in some foods, including beef liver, whole eggs, whole milk, margarine, and some fortified food products such as breakfast cereals. Retinol is a retinoid. Also called preformed vitamin A.
Retinol Activity Equivalent: RAE. A measure of the content and activity of vitamin A in foods.
retinol binding protein: RBP. A molecule that binds to retinol (the form of vitamin A in foods that come from animals) and carries it through the blood to tissues where it is used, and to the liver where it is stored.
retinyl ester: A form in which newly absorbed retinol (the form of vitamin A in foods that come from animals) is stored in the body.
retinyl palmitate: The main form in which retinol (the form of vitamin A in foods that come from animals) is stored in the body.
risk: The chance or probability that a harmful event will occur. In health, for example, the chance that someone will develop a disease or condition.
risk factor: Something that may increase the chance of developing a disease. For example, a diet that is low in calcium and vitamin D is a risk factor for osteoporosis; smoking is a risk factor for lung cancer.
selenium: A mineral required in very small amounts to make important enzymes that are essential for good health. Selenium is found in some foods, including plant foods grown in selenium-rich soil, and some meats and seafood.
sign: An indication of disease that can be seen and/or measured. Examples include high fever, high blood pressure, infection, and coughing up blood.
small intestine: The part of the digestive tract that is located between the stomach and the large intestine.
statistically significant: In medicine, a mathematical measure of difference between two or more groups receiving different treatments that is greater than what might be expected to happen by chance alone.
subclinical: Having to do with the early stage of a disease, before signs and symptoms appear.
supplement: A nutrient that may be added to the diet to increase the intake of that nutrient. Sometimes used to mean dietary supplement.
symptom: A feeling of sickness that an individual can sense, but that cannot be measured by a healthcare professional. Examples include headache, tiredness, stomach ache, depression, and pain.
synthetic: Made by combining parts to make a whole; usually having to do with substances that are artificial or manufactured.
tissue: A group or layer of cells in a living organism that work together to perform a specific function.
toddler: A child between the ages of 12 months and 3 years.
Tolerable Upper Intake Level: UL. The largest daily intake of a nutrient that is considered unlikely to cause harmful side effects for most people in a particular life stage and gender group. Taking more than the UL is not recommended and may be harmful. The amount is established by the Institute of Medicine. For example, the UL for vitamin A is 3,000 micrograms/day. Women who consume more than this amount every day shortly before or during pregnancy have an increased chance (risk) of giving birth to an infant with a birth defect.
toxic: Having to do with poison or something harmful to the body. Toxic substances usually cause unwanted health effects.
toxicity: The degree to which something is poisonous (toxic).
UNICEF: An organization of the United Nations that provides food, clothing, health care, and support to women and children.
urinary tract: The organs involved in making and relieving the body of urine, including the kidneys, ureters, bladder, and urethra.
vegetarianism: The practice of avoiding all or most animal products for environmental, philosophical, and health reasons. Vegetarians (people who practice vegetarianism) eat a diet based on foods that come from plants and may include some dairy products and eggs. See: vegetarian diet.
virus: An organism that can grow and multiply only inside the cells of living humans, plants, or animals. It is able to change (mutate) as it multiplies, which makes viral illnesses difficult to treat. Viruses cause many infections and diseases such as the common cold, AIDS (acquired immunodeficiency syndrome), herpes, and hepatitis.
vitamin: A nutrient that the body needs in small amounts to function and maintain health. Examples are vitamins A, C, and E.
vitamin A: A general term for a group of compounds that includes provitamin A carotenoids (found in foods that come from plants) and retinol (preformed vitamin A found in foods that come from animals). The body can use retinol to make retinal and retinoic acid (other forms of vitamin A). Vitamin A plays an important role in vision, bone growth, reproduction, immunity, cell development, and skin health. Vitamin A is found in some foods, including eggs, liver, fortified milk, cheese, leafy green vegetables (such as spinach, kale, turnip greens, collards, and romaine lettuce), broccoli, dark orange fruits and vegetables (such as apricots, carrots, pumpkin, sweet potatoes, papaya, mango, and cantaloupe), and red bell pepper.
vitamin D: A nutrient that is obtained from the diet and can be made in the skin after exposure to sunlight. Vitamin D acts as a hormone. It helps to form and maintain strong bones, maintain normal blood levels of calcium and phosphorus, and increase calcium absorption; it also helps to maintain a healthy immune system and control cell growth. Vitamin D is found in some foods, including some types of fatty fish, and milk and breakfast cereals that are fortified with vitamin D.
vitamin E: A nutrient needed by the body to help keep the immune system healthy and to repair damage to DNA. It is an antioxidant that protects cells from free radical damage. Vitamin E is found in some foods, including vegetable oils, nuts and seeds, fortified breakfast cereals, and spinach, broccoli, kiwi, and mangos.
white blood cell: WBC. A cell made by the bone marrow that helps the body fight infection and disease. WBCs include lymphocytes, neutrophils, eosinophils, macrophages, and mast cells.
World Health Organization: WHO. An agency of the United Nations that is concerned with worldwide health.
zeaxanthin: A substance found in corn, leafy green vegetables, persimmons, tangerines, seeds, and egg yolk. It is a carotenoid the body cannot use to make vitamin A. It is being studied in the prevention of certain eye diseases (age-related macular degeneration and cataracts).
zinc: A mineral found in most cells of the body. It helps enzymes work properly, helps maintain a healthy immune system, helps maintain the senses of taste and smell, and is needed for wound healing, making DNA, and normal growth and development during pregnancy, childhood, and adolescence. Zinc is found in some foods, including oysters, red meat, poultry, beans, nuts, certain seafood, whole grains, fortified breakfast cereals, and dairy products.