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Vitamin A: What is it?
What foods provide vitamin A?
What are recommended intakes of vitamin A?
When can vitamin A deficiency occur?
Who may need extra vitamin A to prevent a deficiency?
What are some current issues and controversies about vitamin A?
What are the health risks of too much vitamin A?
What are the health risks of too many carotenoids?
Vitamin A intakes and healthful diets
Vitamin A: What is it?
Vitamin A is a group of compounds that play an important role in vision, bone growth, reproduction, cell division, and cell differentiation (in which a cell becomes part of the brain, muscle, lungs, blood, or other specialized tissue.) [1-5]. Vitamin A helps regulate the immune system, which helps prevent or fight off infections by making white blood cells that destroy harmful bacteria and viruses [1,6-10]. Vitamin A also may help lymphocytes (a type of white blood cell) fight infections more effectively.

Vitamin A promotes healthy surface linings of the eyes and the respiratory, urinary, and intestinal tracts [8]. When those linings break down, it becomes easier for bacteria to enter the body and cause infection. Vitamin A also helps the skin and mucous membranes function as a barrier to bacteria and viruses [9-11].

In general, there are two categories of vitamin A, depending on whether the food source is an animal or a plant.

Vitamin A found in foods that come from animals is called preformed vitamin A. It is absorbed in the form of retinol, one of the most usable (active) forms of vitamin A. Sources include liver, whole milk, and some fortified food products. Retinol can be made into retinal and retinoic acid (other active forms of vitamin A) in the body [1].

Vitamin A that is found in colorful fruits and vegetables is called provitamin A carotenoid. They can be made into retinol in the body. In the United States, approximately 26% of vitamin A consumed by men and 34% of vitamin A consumed by women is in the form of provitamin A carotenoids [1]. Common provitamin A carotenoids found in foods that come from plants are beta-carotene, alpha-carotene, and beta-cryptoxanthin [11]. Among these, beta-carotene is most efficiently made into retinol [1,13-15]. Alpha-carotene and beta-cryptoxanthin are also converted to vitamin A, but only half as efficiently as beta-carotene [1].

Of the 563 identified carotenoids, fewer than 10% can be made into vitamin A in the body [12]. Lycopene, lutein, and zeaxanthin are carotenoids that do not have vitamin A activity but have other health promoting properties [1]. The Institute of Medicine (IOM) encourages consumption of all carotenoid-rich fruits and vegetables for their health-promoting benefits.

Some provitamin A carotenoids have been shown to function as antioxidants in laboratory studies; however, this role has not been consistently demonstrated in humans [1]. Antioxidants protect cells from free radicals, which are potentially damaging by-products of oxygen metabolism that may contribute to the development of some chronic diseases [3,14-15].
What foods provide vitamin A?
Retinol is found in foods that come from animals such as whole eggs, milk, and liver. Most fat-free milk and dried nonfat milk solids sold in the United States are fortified with vitamin A to replace the amount lost when the fat is removed [16]. Fortified foods such as fortified breakfast cereals also provide vitamin A. Provitamin A carotenoids are abundant in darkly colored fruits and vegetables. The 2000 National Health and Nutrition Examination Survey (NHANES) indicated that major dietary contributors of retinol are milk, margarine, eggs, beef liver and fortified breakfast cereals, whereas major contributors of provitamin A carotenoids are carrots, cantaloupes, sweet potatoes, and spinach [17].

Vitamin A in foods that come from animals is well absorbed and used efficiently by the body. Vitamin A in foods that come from plants is not as well absorbed as animal sources of vitamin A. Tables 1 and 2 suggest many sources of vitamin A and provitamin A carotenoids [18].

Table 1: Selected animal sources of vitamin A [18]


Vitamin A (IU)*


Liver, beef, cooked, 3 ounces



Liver, chicken, cooked, 3 ounces



Milk, fortified skim, 1 cup



Cheese, cheddar, 1 ounce



Milk, whole (3.25% fat), 1 cup



Egg substitute, ¼ cup



Table 2: Selected plant sources of vitamin A (from beta-carotene) [18]


Vitamin A (IU)*


Carrot juice, canned, ½ cup



Carrots, boiled, ½ cup slices



Spinach, frozen, boiled, ½ cup



Kale, frozen, boiled, ½ cup



Carrots, 1 raw (7½ inches)



Vegetable soup, canned, chunky, ready-to-serve, 1 cup



Cantaloupe, 1 cup cubes



Spinach, raw, 1 cup



Apricots with skin, juice pack, ½ cup



Apricot nectar, canned, ½ cup



Papaya, 1 cup cubes



Mango, 1 cup sliced



Oatmeal, instant, fortified, plain, prepared with water, 1 cup



Peas, frozen, boiled, ½ cup



Tomato juice, canned, 6 ounces



Peaches, canned, juice pack, ½ cup halves or slices



Peach, 1 medium



Pepper, sweet, red, raw, 1 ring (3 inches diameter by ¼ inch thick)



* IU = International Units
** DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowances (RDAs). They were developed to help consumers determine if a food contains a lot or a little of a nutrient. The DV for vitamin A is 5,000 IU. Most food labels do not list vitamin A content. The percent DV (%DV) column in the table above indicates the percentage of the DV provided in one serving. A food providing 5% or less of the DV is a low source while a food that provides 10% to 19% of the DV is a good source. A food that provides 20% or more of the DV is high in that nutrient. It is important to remember that foods that provide lower percentages of the DV also contribute to a healthful diet. For foods not listed in this table, refer to the U.S. Department of Agriculture's Nutrient Database Web site: http://www.nal.usda.gov/fnic/cgi-bin/nut_search.pl.
What are recommended intakes of vitamin A?
Recommendations for vitamin A are provided in the Dietary Reference Intakes (DRIs) developed by the Institute of Medicine (IOM) [1]. DRI is the general term for a set of reference values used for planning and assessing nutrient intake in healthy people. Three important types of reference values included in the DRIs are Recommended Dietary Allowances (RDA), Adequate Intakes(AI), and Tolerable Upper Intake Levels(UL). The RDA recommends the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97% to 98%) healthy individuals in each age and gender group [1]. An AI is set when there are insufficient scientific data to establish an RDA. AIs meet or exceed the amount needed to maintain nutritional adequacy in nearly all people. The UL, on the other hand, is the maximum daily intake unlikely to result in adverse health effects [1].

In Table 3, RDAs for vitamin A are listed as micrograms (mcg) of Retinol Activity Equivalents (RAE) to account for the different biological activities of retinol and provitamin A carotenoids [1]. Table 3 also lists RDAs for vitamin A in International Units (IU), which are used on food and supplement labels (1 RAE = 3.3 IU).

Table 3: Recommended Dietary Allowances (RDAs) for vitamin A


(mcg RAE)

(mcg RAE)

(mcg RAE)

(mcg RAE)

(mcg RAE)


(1,000 IU)






(1,320 IU)






(2,000 IU)







(3,000 IU)

(2,310 IU)

(2,500 IU)

(4,000 IU)



(3,000 IU)

(2,310 IU)

(2,565 IU)

(4,300 IU)

Information is insufficient to establish an RDA for vitamin A for infants. AIs have been established based on the amount of vitamin A consumed by healthy infants fed breast milk (Table 4) [1].

Table 4: Adequate Intakes (AIs) for vitamin A for infants

Age (months)

Males and females (mcg RAE)


400 (1,320 IU)


500 (1,650 IU)

The NHANES III survey (1988-1994) found that most Americans consume recommended amounts of vitamin A [19]. More recent NHANES data (1999-2000) show average adult intakes to be about 3,300 IU per day, which also suggests that most Americans get enough vitamin A [20].

There is no RDA for beta-carotene or other provitamin A carotenoids. The IOM states that consuming 3 mg to 6 mg of beta-carotene daily (equivalent to 833 IU to 1,667 IU vitamin A) will maintain blood levels of beta-carotene in the range associated with a lower risk of chronic diseases [1]. A diet that provides five or more servings of fruits and vegetables per day and includes some dark green and leafy vegetables and deep yellow or orange fruits should provide sufficient beta-carotene and other carotenoids.
When can vitamin A deficiency occur?
Vitamin A deficiency is common in developing countries but rarely seen in the United States. Approximately 250,000 to 500,000 malnourished children in the developing world become blind each year from a deficiency of vitamin A [1]. In the United States, vitamin A deficiency is most often associated with strict dietary restrictions and excess alcohol intake [21]. Severe zinc deficiency, which is also associated with strict dietary limitations, often accompanies vitamin A deficiency. Zinc is required to make retinol binding protein (RBP) which transports vitamin A. Therefore, a deficiency in zinc limits the body's ability to move vitamin A stores from the liver to body tissues [1].

Night blindness is one of the first signs of vitamin A deficiency. In ancient Egypt, it was known that night blindness could be cured by eating liver, which was later found to be a rich source of the vitamin [2]. Vitamin A deficiency contributes to blindness by making the cornea very dry and damaging the retina and cornea [22].

Vitamin A deficiency diminishes the ability to fight infections. In countries where such deficiency is common and immunization programs are limited, millions of children die each year from complications of infectious diseases such as measles [23]. In vitamin A-deficient individuals, cells lining the lungs lose their ability to remove disease-causing microorganisms. This may contribute to the pneumonia associated with vitamin A deficiency [2,6-7].

There is increased interest in early forms of vitamin A deficiency, described as low storage levels of vitamin A that do not cause obvious deficiency symptoms. This mild degree of vitamin A deficiency may increase children's risk of developing respiratory and diarrheal infections, decrease growth rate, slow bone development, and decrease likelihood of survival from serious illness [24-25]. Children in the United States who are considered to be at increased risk for subclinical vitamin A deficiency include:

  • toddlers and preschool age children;
  • children living at or below the poverty level;
  • children with inadequate health care or immunizations;
  • children living in areas with known nutritional deficiencies;
  • recent immigrants or refugees from developing countries with high incidence of vitamin A deficiency or measles; and
  • children with diseases of the pancreas, liver, or intestines, or with inadequate fat digestion or absorption.

A deficiency can occur when vitamin A is lost through chronic diarrhea and through an overall inadequate intake, as is often seen with protein-energy malnutrition. Low blood retinol concentrations indicate depleted levels of vitamin A. This occurs with vitamin A deficiency but also can result from an inadequate intake of protein, calories, and zinc, since these nutrients are needed to make RBP [1]. Iron deficiency can also affect vitamin A metabolism, and iron supplements provided to iron-deficient individuals may improve body stores of vitamin A and iron [1].

Excess alcohol intake depletes vitamin A stores. Also, diets high in alcohol often do not provide recommended amounts of vitamin A [1]. It is very important for people who consume excessive amounts of alcohol to include good sources of vitamin A in their diets. Vitamin A supplements may not be recommended for individuals who abuse alcohol, however, because their livers may be more susceptible to potential toxicity from high doses of vitamin A [26]. A medical doctor will need to evaluate this situation and determine the need for vitamin A supplements.
Who may need extra vitamin A to prevent a deficiency?
Vitamin A deficiency rarely occurs in the United States, but the World Health Organization (WHO) and the United Nations Children's Fund (UNICEF) recommend vitamin A administration for all children diagnosed with measles in communities where vitamin A deficiency is a serious problem and where death from measles is greater than 1%. In 1994, the American Academy of Pediatrics recommended vitamin A supplements for two subgroups of children likely to be at high risk for subclinical vitamin A deficiency: children aged 6 months to 24 months who are hospitalized with measles, and hospitalized children older than 6 months [27].

Fat malabsorption can result in diarrhea and prevent normal absorption of vitamin A. Over time this may result in vitamin A deficiency. Those conditions include:

  • Celiac disease:
    Often referred to as sprue, celiac disease is a genetic disorder. People with celiac disease become sick when they eat a protein called gluten found in wheat and some other grains. In celiac disease, gluten can trigger damage to the small intestine, where most nutrient absorption occurs. Approximately 30% to 60% of people with celiac disease have gastrointestinal-motility disorders such as diarrhea [28].They must follow a gluten-free diet to avoid malabsorption and other symptoms.
  • Crohn's disease:
    This inflammatory bowel disease affects the small intestine. People with Crohn's disease often experience diarrhea, fat malabsorption, and malnutrition [29].
  • Pancreatic disorders:
    Because the pancreas secretes enzymes that are important for fat absorption, pancreatic disorders often result in fat malabsorption [30-31]. Without these enzymes, it is difficult to absorb fat. Many people with pancreatic disease take pancreatic enzymes in pill form to prevent fat malabsorption and diarrhea.

Healthy adults usually have a reserve of vitamin A stored in their livers and should not be at risk of deficiency during periods of temporary or short-term fat malabsorption. Long-term problems absorbing fat, however, may result in deficiency. In these instances physicians may recommend additional vitamin A [9].

Vegetarians who do not consume eggs and dairy foods need provitamin A carotenoids to meet their need for vitamin A [1]. They should include a minimum of five servings of fruits and vegetables in their daily diet and regularly choose dark green leafy vegetables and orange and yellow fruits to consume recommended amounts of vitamin A.
What are some current issues and controversies about vitamin A?
Vitamin A, beta carotene, and cancer
Dietary intake studies suggest an association between diets rich in beta-carotene and vitamin A and a lower risk of many types of cancer [32]. A higher intake of green and yellow vegetables or other food sources of beta carotene and/or vitamin A may decrease the risk of lung cancer [2,33-34]. However, a number of studies that tested the role of beta-carotene supplements in cancer prevention did not find them to protect against the disease. In the Alpha-Tocopherol Beta-Carotene (ATBC) Cancer Prevention Study, more than 29,000 men who regularly smoked cigarettes were randomized to receive 20 mg beta-carotene alone, 50 mg alpha-tocopherol alone, supplements of both, or a placebo for 5 to 8 years. Incidence of lung cancer was 18% higher among men who took the beta-carotene supplement. Eight percent more men in this group died, as compared to those receiving other treatments or placebo [35]. Similar results were seen in the Carotene and Retinol Efficacy Trial (CARET), a lung cancer chemoprevention study that provided subjects with supplements of 30 mg beta-carotene and 25,000 IU retinyl palmitate (a form of vitamin A) or a placebo. This study was stopped after researchers discovered that subjects receiving beta-carotene had a 46% higher risk of dying from lung cancer [36-37].

The IOM states that "beta-carotene supplements are not advisable for the general population," although they also state that this advice "does not pertain to the possible use of supplemental beta-carotene as a provitamin A source for the prevention of vitamin A deficiency in populations with inadequate vitamin A" [1].

Vitamin A and osteoporosis
Osteoporosis, a disorder characterized by porous and weak bones, is a serious health problem for more than 10 million Americans, 80% of whom are women. Another 18 million Americans have decreased bone density which precedes the development of osteoporosis. Many factors increase the risk for developing osteoporosis, including being female, thin, inactive, at advanced age, and having a family history of osteoporosis. An inadequate dietary intake of calcium, cigarette smoking, and excessive intake of alcohol also increase the risk [38-40].

Researchers are now examining a potential new risk factor for osteoporosis: an excess intake of vitamin A. Animal, human, and laboratory research suggests an association between greater vitamin A intake and weaker bones [40-41]. Worldwide, the highest incidence of osteoporosis occurs in northern Europe, a population with a high intake of vitamin A [42]. However, decreased biosynthesis of vitamin D associated with lower levels of sun exposure in this population may also contribute to this finding.

One small study of nine healthy individuals in Sweden found that the amount of vitamin A in one serving of liver may impair the ability of vitamin D to promote calcium absorption [43]. To further test the association between excess dietary intakes of vitamin A and increased risk for hip fractures, researchers in Sweden compared bone mineral density and retinol intake in approximately 250 women with a first hip fracture to 875 age-matched controls. They found that a dietary retinol intake greater than 1,500 mcg/day (more than twice the recommended intake for women) was associated with reduced bone mineral density and increased risk of hip fracture as compared to women who consumed less than 500 mcg/day [44].

This issue was also examined by researchers with the Nurses Health Study, who looked at the association between vitamin A intake and hip fractures in over 72,000 postmenopausal women. Women who consumed the most vitamin A in foods and supplements (3,000 mcg or more per day as retinol equivalents, which is over three times the recommended intake) had a significantly increased risk of experiencing a hip fracture as compared to those consuming the least amount (less than 1,250 mcg/day). The effect was lessened by use of estrogens. These observations raise questions about the effect of retinol because retinol intakes greater than 2,000 mcg/day were associated with an increased risk of hip fracture as compared to intakes less than 500 mcg [45].

A longitudinal study in more than 2,000 Swedish men compared blood levels of retinol to the incidence of fractures in men. The investigators found that the risk of fractures was greatest in men with the highest blood levels of retinol (more than 75 mcg per deciliter [dL]). Men with blood retinol levels in the 99th percentile (greater than 103 mcg per dL) had an overall risk of fracture that exceeded the risk among men with lower levels of retinol by a factor of seven [46]. High vitamin A intake, however, does not necessarily equate to high blood levels of retinol. Age, gender, hormones, and genetics also influence these levels. Researchers did not find any association between blood levels of beta-carotene and risk of hip fracture. Researchers' findings, which are consistent with the results of animal, in vitro (laboratory), and epidemiologic studies, suggest that intakes above the UL, or approximately two times that of the RDA for vitamin A, may pose subtle risks to bone health that require further study.

The Centers for Disease Control and Prevention (CDC) reviewed data from NHANES III (1988-94) to determine whether there was any association between bone mineral density and blood levels of retinyl esters, a form of vitamin A [47]. No significant associations between blood levels of retinyl esters and bone mineral density in 5,800 subjects were found.

There is no evidence of an association between beta-carotene intake, especially from fruits and vegetables, and increased risk of osteoporosis. Current evidence points to a possible association with vitamin A as retinol only. If you have specific questions regarding your intake of vitamin A and risk of osteoporosis, discuss this information with your physician or other qualified healthcare provider to determine what's best for your personal health.
What are the health risks of too much vitamin A?
Hypervitaminosis A refers to high storage levels of vitamin A in the body that can lead to toxic symptoms. There are four major adverse effects of hypervitaminosis A: birth defects, liver abnormalities, reduced bone mineral density that may result in osteoporosis (see the previous section), and central nervous system disorders [1,48-49].

Toxic symptoms can also arise after consuming very large amounts of preformed vitamin A over a short period of time. Signs of acute toxicity include nausea and vomiting, headache, dizziness, blurred vision, and muscular uncoordination [1,48-49]. Although hypervitaminosis A can occur when large amounts of liver are regularly consumed, most cases result from taking excess amounts of the nutrient in supplements.

The IOM has established Tolerable Upper Intake Levels (ULs) for vitamin A that apply to healthy populations [1]. The UL was established to help prevent the risk of vitamin A toxicity. The risk of adverse health effects increases at intakes greater than the UL. The UL does not apply to malnourished individuals receiving vitamin A either periodically or through fortification programs as a means of preventing vitamin A deficiency. It also does not apply to individuals being treated with vitamin A by medical doctors for diseases such as retinitis pigmentosa.

Table 5: Tolerable Upper Intake Levels (ULs) for retinol








(2,000 IU)






(2,000 IU)






(3,000 IU)






1,700 (5610 IU)







2,800 (9,240 IU)

2,800 (9,240 IU)

2,800 (9,240 IU)

2,800 (9,240 IU)



3,000 (10,000 IU)

3,000 (10,000 IU)

3,000 (10,000 IU)

3,000 (10,000 IU)

Retinoids are compounds that are chemically similar to vitamin A. Over the past 15 years, synthetic retinoids have been prescribed for acne, psoriasis, and other skin disorders [50]. Isotretinoin (Roaccutane® or Accutane®) is considered an effective anti-acne therapy. At very high doses, however, it can be toxic, which is why this medication is usually saved for the most severe forms of acne [51-53]. The most serious consequence of this medication is birth defects. It is extremely important for sexually active females who may become pregnant and who take these medications to use an effective method of birth control. Women of childbearing age who take these medications are advised to undergo monthly pregnancy tests to make sure they are not pregnant.
What are the health risks of too many carotenoids?
Provitamin A carotenoids such as beta-carotene are generally considered safe because they are not associated with specific adverse health effects. Their conversion to vitamin A decreases when body stores are full. A high intake of provitamin A carotenoids can turn the skin yellow, but this is not considered dangerous to health.

Clinical trials that associated beta-carotene supplements with a greater incidence of lung cancer and death in current smokers raise concerns about the effects of beta-carotene supplements on long-term health; however, conflicting studies make it difficult to interpret the health risk. For example, the Physicians Health Study compared the effects of taking 50 mg beta-carotene every other day to a placebo in over 22,000 male physicians and found no adverse health effects [54]. Also, a trial that tested the ability of four different nutrient combinations to help prevent the development of esophageal and gastric cancers in 30,000 men and women in China suggested that after five years those participants who took a combination of beta-carotene, selenium, and vitamin E had a 13% reduction in cancer deaths [55]. In one lung cancer trial, men who consumed more than 11 grams/day of alcohol (approximately one drink per day) were more likely to show an adverse response to beta-carotene supplements [1], which may suggest a potential relationship between alcohol and beta-carotene.

The IOM did not set ULs for carotene or other carotenoids. Instead, it concluded that beta-carotene supplements are not advisable for the general population. As stated earlier, however, they may be appropriate as a provitamin A source for the prevention of vitamin A deficiency in specific populations [1].
Vitamin A intakes and healthful diets
According to the 2005 Dietary Guidelines for Americans, "Nutrient needs should be met primarily through consuming foods. Foods provide an array of nutrients and other compounds that may have beneficial effects on health. In certain cases, fortified foods and dietary supplements may be useful sources of one or more nutrients that otherwise might be consumed in less than recommended amounts. However, dietary supplements, while recommended in some cases, cannot replace a healthful diet [56]." For more information about building a healthful diet, refer to the Dietary Guidelines for Americans (http://www.health.gov/dietaryguidelines/dga2005/document/pdf/DGA2005.pdf) and the U.S. Department of Agriculture's food guidance system (My Pyramid; http://www.mypyramid.gov).



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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 physical, mental, and social 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 substance 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. It is a carotenoid that can be made into vitamin A in the body.
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 required for normal growth and strength of bones and teeth, for nerves and enzymes to function properly, and for blood clotting.
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, and barley) 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 product label to describe the recommended levels of intake of a nutrient. The percent Daily Value (% DV) represents how much of a nutrient is provided in one serving of the food or dietary supplement. For example, the DV for calcium is 1,000 mg (milligrams); a food that has 200 mg of calcium per serving would state on the label that the % DV for calcium is 20%.
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 insufficient amount, a shortage, or an inadequacy.
diagnose - The process of using signs and symptoms to identify a disease.
diarrhea - Frequent and watery bowel movements.
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 food processing or to replace nutrients lost when a food product is produced or stored that may be lacking in the overall diet (such as folate, vitamins A and D, and calcium). 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 in a bone.
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 Alzheimer’s, Parkinson’s, and Lou Gehrig’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 - Invasion and multiplication of germs in the body. An infection can occur in any part of the body and can spread throughout the body. The germs may be bacteria, viruses, yeast, or fungi. An infection can cause a fever and other problems, depending on where it occurs. When the body’s natural defense system is strong, it can often fight off germs and prevent infection.
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 for 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 (such as protein, fat, carbohydrate, a vitamin, or mineral) that is found in food. Nutrients are used by the body to function and maintain health.
nutritional - Having to do with nutrition (eating, digesting, and absorbing the nutrients in food, and the health and disease consequences).
osteoporosis - A condition that is characterized by a decrease in bone mass and bone density, causing bones to become fragile and 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, other 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 is needed for the body to work properly. 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 daily dietary intake level estimated by the Institute of Medicine to meet the nutrient requirements of most healthy individuals in a particular life stage and gender group. For example, the RDA for vitamin C is 75 mg/day for women older than 18 years.
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.
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 as a synonym of dietary supplement.
symptom - An indication of disease that an individual can feel, but that cannot be measured objectively by a health care professional. Examples include headache, fatigue, indigestion, 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 state of being poisonous (toxic).
United Nations Children's Fund - UNICEF. An organization of the United Nations created in 1946 to provide food, clothing, and health care to children facing famine and disease. It also provides support for education; advocates for the protection of children's and women's rights; helps developing countries deliver services to victims of war, disaster, extreme poverty, violence, and disability; and promotes the equal rights and full participation of women and girls in the political, social, and economic development of their communities.
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. Some also may avoid wearing clothes made from animals or using other products that come from animals. 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 multiples, which makes viral illnesses difficult to treat. Viruses cause many infections and diseases such as the common cold, acquired immunodeficiency syndrome (AIDS), 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 fat-soluble 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 fat-soluble vitamin with antioxidant properties that is important for the proper function of nerves and muscles.
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.

Reasonable care has been taken in preparing this document, and the information provided herein is believed to be accurate. However, this information is not intended to constitute an "authoritative statement" under Food and Drug Administration rules and regulations.

About ODS
The mission of the Office of Dietary Supplements (ODS) is to strengthen knowledge and understanding of dietary supplements by evaluating scientific information, stimulating and supporting research, disseminating research results, and educating the public to foster an enhanced quality of life and health for the U.S. population.

General Safety Advisory
Health professionals and consumers need credible information to make thoughtful decisions about eating a healthful diet and using vitamin and mineral supplements. To help guide those decisions, registered dietitians at the NIH Clinical Center developed a series of Fact Sheets in conjunction with ODS. These Fact Sheets provide responsible information about the role of vitamins and minerals in health and disease. Each Fact Sheet in this series received extensive review by recognized experts from the academic and research communities.

The information is not intended to be a substitute for professional medical advice. It is important to seek the advice of a physician about any medical condition or symptom. It is also important to seek the advice of a physician, registered dietitian, pharmacist, or other qualified health professional about the appropriateness of taking dietary supplements and their potential interactions with medications.

The Clinical Nutrition Service and the ODS thank the expert scientific reviewers for their role in ensuring the scientific accuracy of the information discussed in these Fact Sheets, along with the Nutrition Education Subcommittee of the NIH, the U.S. Department of Agriculture (USDA) Dietary Guidance Working Group, and the Department of Health and Human Services Nutrition Policy Board Committee on Dietary Guidance.

Reviewers of this Vitamin A Fact Sheet:
James Allen Olson, PhD, Iowa State University (deceased)
Cheryl L. Rock, PhD, University of California, San Diego
A. Catharine Ross, PhD, The Pennsylvania State University
Barbara A. Underwood, PhD

Information Provided By:
Office of Dietary Supplements
National Institutes of Health
Bethesda, Maryland 20892 USA
Web: http://ods.od.nih.gov
E-mail: ods@nih.gov