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vitamin A

What can high-vitamin A foods do for you?

  • Preserve and improve your eyesight
  • Help you fight off viral infections

What events can indicate a need for more high-vitamin A foods?

  • Frequent viral infections
  • Night blindness
  • Goose bump-like appearance of the skin

Although vitamin A is found only in foods of animal origin, some fruits and vegetables contain compounds, called cartenoids, that can be converted into vitamin A by your body. Food sources of preformed vitamin A include calf liver, milk, and eggs.

Description

What is vitamin A?

Vitamin A, identified in 1913, was the first fat-soluble vitamin to be discovered. A light yellow crystalline compound, vitamin A is also known as retinol, a name given in reference to the participation of this compound in the functions of the retina of the eye. Vitamin A has also been called the “anti-infective” vitamin due to its role in supporting the activities of the immune system.

While retinol, or preformed vitamin A, occurs only in foods of animal origin, fruits and vegetables that contain certain carotenoids also provide vitamin A activity. Carotenoids are plant pigments, responsible for the red, orange, and yellow color of fruits and vegetables.

The body can convert certain members of the carotenoid family, including beta-carotene, alpha-carotene, and gamma-carotene, into vitamin A. These carotenoids are sometimes referred to as "provitamin A," and retinol as "preformed vitamin A."

How it Functions

What is the function of vitamin A?

While vitamin A is best known for its vital role in vision, this vitamin also participates in physiological activities related to the immune system, maintenance of epithelial and mucosal tissues, growth, reproduction, and bone development. In food, vitamin A typically occurs as a fat compound called retinyl palmitate. The body converts retinyl palmitate to three metabolically active forms of the vitamin: retinol, retinal, and retinoic acid.

Vision support

The human retina contains four kinds of photopigments that store vitamin A compounds. One of these pigments, called rhodopsin, is located in the rod cells of the retina. Rhodopsin allows the rod cells to detect small amounts of light, and, thus, plays a fundamental role in the adaptation of the eye to low-light conditions and night vision.

Retinal, the aldehyde form of the vitamin, participates in the synthesis of rhodopsin, and in the series of chemical reactions that causes visual excitation, which is triggered by light striking the rod cells. The remaining three pigments, collectively known as iodopsins, are found in the cone cells of the retina and are responsible for day vision.

Immune function support

Vitamin A stimulates several immune system activities, possibly by promoting the growth, and preventing the stress-induced shrinkage, of the thymus gland. Vitamin A is known to enhance the function of white blood cells, increase the response of antibodies to antigens, and to have anti-viral activity.

In addition, retinoic acid is needed to maintain the normal structure and function of epithelial and mucosal tissues, which are found in the lungs, trachea, skin, oral cavity, and gastrointestinal tract. These tissues, when healthy and intact, serve as the first line of defense for the immune system, providing a protective barrier that disease-causing microorganisms cannot penetrate.

Cell growth support

Vitamin A is also necessary for normal cell growth and development. Although the mechanisms by which vitamin A promotes cell growth and development are not yet fully understood, it is known that retinoic acid is necessary for the synthesis of many glycoproteins, which control cellular adhesion (the ability of cells to attach to one another), cell growth and cell differentiation.

Other roles for vitamin A

It is also known that vitamin A is essential for reproductive processes in both males and females and plays a role in normal bone metabolism. In addition, some of the most cutting-edge research in the field of genetics has been examining the role of vitamin A (in the form of retinoic acid) in regulating genetic events.

Deficiency Symptoms

What are deficiency symptoms for vitamin A?

Dietary deficiency of vitamin A is quite common in developing countries, and is associated with the high incidence of blindness, viral infections, and child mortality that occurs in impoverished populations. Vitamin A deficiency primarily affects the health of the skin, hair, eyes, and immune system, though loss of appetite, bone abnormalities, and growth retardation are also associated with inadequate intake of this vitamin.

A tell-tale sign of vitamin A deficiency is hyperkeratosis, a goose bump-like appearance of the skin caused by excessive production of keratin (a protein found in skin) that blocks hair follicles. In initial stages, hyperkeratosis is found on the forearms and thighs, where the skin becomes dry, scaly, and rough. In advances stages, hyperkeratosis affects the whole body, causing hair loss.

Due to the important role of vitamin A in supporting the functions of the immune system, individuals with insufficient intake of this vitamin often experience increased susceptibility to viral infections, most notably measles, chicken pox, pneumonia, and respiratory syncytial virus (RSV).

Prolonged vitamin A deficiency can lead to night blindness, due to impaired production of rhodopsin, the compound in the retina responsible for detecting small amounts of light. Xerophthalmia, a condition characterized by changes to the conjunctiva and cornea of the eye, also results from prolonged vitamin A deficiency, and is a major cause of blindness in developing nations.

Toxicity Symptoms

What are toxicity symptoms for vitamin A?

Vitamin A can cause side effects when taken in excessive amounts. Most causes of vitamin A toxicity are due to accidental ingestion of doses exceeding 660,000 IU (200 mg of retinol equivalents) and 330,000 IU (100 mg of retinol equivalents) by adults and children, respectively.

Adverse reactions to acute ingestion are usually temporary and include loss of appetite, irritability, fatigue, weakness and vomiting. Chronic vitamin A toxicity may occur following many months of daily intake of the vitamin in amounts exceeding 14,000 IU (4.2 mg or retinol equivalents) in children and 25,000 IU in adults, and is most likely to develop in individuals taking high doses of vitamin A compounds to treat skin disorders, or in those with poor liver function.

The symptoms of chronic toxicity in infants include growth retardation of the long bones (for example, the femur bone in the leg) and premature epiphyseal bone closing. In adults, vitamin A toxicity causes a variety of health conditions, including dry and itchy skin, dry and brittle fingernails, hair loss, headaches, visual changes, bone and muscle pain, fatigue, irritability, depression, schizophrenia, fever, liver damage, anemia, and/or loss of appetite. In most cases, these maladies begin to disappear as soon as vitamin A intake is decreased.

For all of the above reasons, in 2000 the National Academy of Sciences set Tolerable Upper Intake Levels (ULs) for preformed vitamin A as follows:

  • Children 3 years or younger, 600 micrograms (2,000 IU) per day
  • Children 4-8 years, 900 micrograms (3,000 IU)
  • Children 9-14 years, 1,700 micrograms (5,666 IU)
  • Teenagers 14-18 years, 2,800 mcg (9,332 IU)
  • Adults 19 years and older, 3,000 mcg (10,000 IU)
  • Pregnant or lactating women 18 years or younger, 2,800 mcg (9,332 IU)
  • Pregnant or lactating women 19 years or older, 3,000 mcg (10,000 IU)

It is important to emphasize that although excessive intake of vitamin A by children and adults does not usually cause irreversible damage, vitamin A is toxic to the fetus and can cause severe birth defects, including cleft palate and spina bifida, when taken in daily doses exceeding 10,000 IU by pregnant women. It is recommended, therefore, that women who may become pregnant limit intake of supplemental vitamin A to no more than 5,000 IU per day.

Impact of Cooking, Storage and Processing

How do cooking, storage, or processing affect vitamin A?

Neither cooking nor storage significantly affects the amount or availability of preformed vitamin A in foods.

Factors that Affect Function

What factors might contribute to a deficiency of vitamin A?

Since vitamin A is a fat-soluble vitamin, vitamin A deficiency may be caused by a diet that is extremely low in fat and/or the presence of medical conditions that cause a reduction in the ability to absorb dietary fat, such as pancreatic enzyme deficiency, Crohn’s disease, celiac sprue, cystic fibrosis, surgical removal of part or all of the stomach, gall bladder disease, and liver disease.

In addition, chronic diarrhea caused by gastrointestinal infections and/or intestinal parasites may contribute to vitamin A deficiency. Viral infections, specifically the measles, decrease vitamin A status. In addition, exposure to certain toxic chemicals (for example, polybrominated biphenyls and dioxin) enhances the breakdown of vitamin A by the liver.

Inadequate intake of protein contributes to vitamin A deficiency (see further explanation in the section on Nutrient Interactions).

Drug-Nutrient Interactions

What medications affect vitamin A?

The following medications impact the absorption, utilization and/or excretion of vitamin A:

  • The class of cholesterol-lowering medications known as HMG-CoA reductase inhibitors (Lipitor, Lescol, Mevacor, Provachol, Zocor) may increase blood levels of Vitamin A
  • Bile acid sequestrants (Cholestyramine, Colestid) are used to reduce cholesterol levels. These drugs may interfere with the fat-soluble vitamins, including vitamin A.
  • Medroxyprogesterone (Provera, Depo-Provera), a contraceptive, may increase blood levels of vitamin A
  • Neomycin, an antibacterial drug, may decrease the absorption of vitamin A.

Isotretinoin and tretinoin (Retin-A, Vitinoin, Vesanoid) are used in the treatment of severe acne and certain types of skin cancer. These drugs are similar in chemical structure to vitamin A. To prevent the symptoms associated with vitamin A toxicity, individuals taking these medications should avoid taking supplemental vitamin A in doses exceeding 10,000 IU per day.

Nutrient Interactions

How do other nutrients interact with vitamin A?

The transport and utilization of vitamin A is dependent upon several vitamin A binding proteins. Because a sufficient dietary intake of protein is required for the manufacture of these binding proteins, inadequate protein intake may result in vitamin A deficiency. In addition, adequate intake of dietary fat and zinc is necessary for the absorption and utilization of vitamin A.

Because vitamin A deficiency causes anemia, it is believed that vitamin A impacts the metabolism of iron, though the mechanism through which this occurs has not yet been defined.

Excess vitamin A interferes with the absorption of vitamin K, a fat-soluble vitamin necessary for blood clotting.

Health Conditions

What health conditions require special emphasis on vitamin A?

Vitamin A may play a role in the prevention and/or treatment of the following health conditions:
  • Acne
  • AIDS
  • Alcoholism
  • Atopic dermatitis
  • Cataracts
  • Cervical dysplasia
  • Diabetes
  • Dry Eyes
  • Fibrocycstic breast disease
  • Hyperkeratosis
  • Inflammaotory bowel disease
  • Kaposi's sarcoma
  • Leukoplakia
  • Osteoarthritis
  • Otitis media (ear infection)
  • Poor vision
  • Psoriasis
  • Thyroid disorders
  • Ulcers
  • Vaginitis
  • Varicose veins
  • Viral infections

Form in Dietary Supplements

What forms of vitamin A are found in dietary supplements?

As a vitamin supplement, vitamin A is available as retinol and retinyl-palmitate. Retinoic acid is the form of vitamin A found in medications prescribed for the treatment of skin disorders.

Food Sources

Introduction to Nutrient Rating System Chart

The following chart shows the foods which are either excellent, very good or good sources of this nutrient. Next to each food name you will find the following information: the serving size of the food; the number of calories in one serving; DV% (percent daily value) of the nutrient contained in one serving (similar to other information presented in the website, this DV is calculated for 25-50 year old healthy woman); the nutrient density rating; and the food's World's Healthiest Foods Rating. Underneath the chart is a table that summarizes how the ratings were devised. Read more about our Nutrient Rating System.

Foods Ranked as quality sources of:
vitamin A
Food Serving
Size
Cals Amount
(IU)
DV
(%)
Nutrient
Density
World's
Healthiest
Foods Rating
Carrots, Raw 1 cup 52.5 34317.40 686.3 235.5 excellent
Spinach (boiled, with salt) 1 cup 41.4 14742.00 294.8 128.2 excellent
Greens, Turnip, Cooked 1 cup 28.8 7917.12 158.3 99.0 excellent
Kale, Fresh, Boiled 1 cup 36.4 9620.00 192.4 95.1 excellent
Red Bell Peppers (sliced, raw) 1 cup 24.8 5244.00 104.9 76.0 excellent
Greens, Mustard, Boiled 1 cup 21.0 4243.40 84.9 72.7 excellent
Lettuce, Romaine 2 cup 15.7 2912.00 58.2 66.9 excellent
Liver, Calf 4 oz-wt 187.1 30485.26 609.7 58.7 excellent
Chard, Boiled 1 cup 35.0 5493.25 109.9 56.5 excellent
Parsley, Fresh 1 oz-wt 10.2 1474.20 29.5 52.0 excellent
Sweet Potato (small, baked with skin) 1 each 95.4 13107.70 262.2 49.5 excellent
Pepper, Cayenne, Dried 2 tsp 11.2 1470.24 29.4 47.3 excellent
Collard Greens, Boiled, Drained 1 cup 49.4 5945.10 118.9 43.3 excellent
Cantaloupe 1 cup 56.0 5158.40 103.2 33.2 excellent
Squash, Winter, All Varieties 1 cup 80.0 7291.85 145.8 32.8 excellent
Peppermint Leaves, Fresh 1 oz-wt 19.9 1204.31 24.1 21.8 excellent
Apricots, Raw 1 each 16.8 914.20 18.3 19.6 excellent
Broccoli (pieces, steamed) 1 cup 43.7 2280.72 45.6 18.8 excellent
Basil, Ground 2 tsp 7.5 281.24 5.6 13.5 very good
Tomato, Red, Raw, Ripe 1 cup 37.8 1121.40 22.4 10.7 excellent
Oregano, Ground 2 tsp 9.2 207.08 4.1 8.1 good
Asparagus, Boiled 1 cup 43.2 970.20 19.4 8.1 excellent
Chili Peppers, Red, Dried 2 tsp 25.5 531.60 10.6 7.5 very good
Green Snap/String Beans, Boiled 1 cup 43.8 832.50 16.6 6.9 very good
Brussels Sprouts, Boiled 1 cup 60.8 1121.64 22.4 6.6 very good
Cucumber, Raw 1 cup 13.5 223.60 4.5 6.0 good
Squash, Summer, All Varieties 1 cup 36.0 516.60 10.3 5.2 very good
Grapefruit 0.50 each 60.0 750.00 15.0 4.5 very good
Watermelon 1 cup 48.6 556.32 11.1 4.1 very good
Celery, Raw 1 cup 19.2 160.80 3.2 3.0 good
Prunes, Dried 0.25 cup 101.6 844.48 16.9 3.0 good
Papaya 1 each 118.6 863.36 17.3 2.6 good
Green Peas-Boiled 1 cup 134.4 955.20 19.1 2.6 good
Cabbage (shredded, boiled) 1 cup 33.0 198.00 4.0 2.2 good
Plum 1 each 36.3 213.18 4.3 2.1 good
Oranges 1 each 61.6 268.55 5.4 1.6 good
Milk, Cow, 2% 1 cup 121.2 500.20 10.0 1.5 good
World's Healthiest
Foods Rating
Rule
excellent DV>=75% OR Density>=7.6 AND DV>=10%
very good DV>=50% OR Density>=3.4 AND DV>=5%
good DV>=25% OR Density>=1.5 AND DV>=2.5%

Public Health Recommendations

What are current public health recommendations for vitamin A?

Vitamin A was originally measured in International Units, which still appear on food and supplement labels. However, it is now common practice to also measure the amount of vitamin A activity available from a given food or supplement, as expressed in micrograms (mcg) of retinol equivalents (RE), which allows consumers to easily determine the vitamin A activity of foods containing the provitamain A carotenoids. When converting between these two units of measure, 1 retinol equivalent (or RE) is equal to 3.33 International Units (or IU) of preformed vitamin A.

In 2000, the National Academy of Sciences established the following Adequate Intake (AI) levels for consumption of vitamin A by infants:

  • Males and females 0-6 months: 400 micrograms (1,333 IU)
  • Males and females 7-12 months: 500 micrograms (1,666 IU)

In 2000, the National Academy of Sciences established the following Recommended Dietary Allowances (RDAs) for consumption of vitamin A by children and adults:

  • Males and females, 1-3 years: 1,000 IU (300 mcg of retinol equivalents)
  • Males and females, 4-8 years: 1,333 IU (400 mcg of retinol equivalents)
  • Males and females, 9-13 years: 2,000 IU (600 mcg of retinol equivalents)
  • Males and females, 14 years and older: 3,000 IU (900 mcg of retinol equivalents)

In 2000, the National Academy of Sciences established the following Estimated Average Requirements (EARs) for consumption of vitamin A by pregnant and lactating women:

  • Pregnant women: 1,767 IU (530 mcg of retinol equivalents)
  • Lactating women, 18 years or younger: 2,933 IU (880 mcg of retinol equivalents)
  • Lactating women, 19 years or older: 3,000 IU (900 mcg of retinol equivalents)

References

  • Blaner WS. Retinol-binding protein: the serum transport protein for vitamin A. Endocr Rev 1989 Aug;10(3):308-16.
  • Chetyrkin SV. [Transport and metabolism of vitamin A]. Ukr Biokhim Zh 2000 May-2000 Jun 30;72(3):12-24.
  • Groff JL, Gropper SS, Hunt SM. Advanced Nutrition and Human Metabolism. West Publishing Company, New York, 1995.
  • Harrison EH. Lipases and carboxylesterases: possible roles in the hepatic metabolism of retinol. Annu Rev Nutr 1998;18:259-76.
  • Kato S. [Transcriptional control by nuclear vitamin A/D receptors]. Tanpakushitsu Kakusan Koso 2000 Jun;45(9 Suppl):1534-45.
  • Lininger SW, et al. A-Z guide to drug-herb-vitamin interactions. Prima Health, Rocklin, CA, 2000.
  • Maden M. The role of retinoic acid in embryonic and post-embryonic development. Proc Nutr Soc 2000 Feb;59(1):65-73.
  • Moriwaki H, Okuno M, Nishiwaki R, Shiratori Y. [Retinol-binding protein (RBP)]. Nippon Rinsho 1999 Aug;57 Suppl:279-81.
  • Pizzorno J, Murray M. The Textbook of Natural Medicine. The Textbook of Natural Medicine.
  • Slamenova D, Chalupa I, Robichova S et al. Effect of dietary intake of vitamin A or E on the level of DNA damage, chromosomal aberrations, and micronuclei induced in freshly isolated rat hepatocytes by different carcinogens. Nutr Cancer 2002;42(1):117-24.
  • Smith J, Steinemann TL. Vitamin A deficiency and the eye. Int Ophthalmol Clin 2000 Fall;40(4):83-91.
  • Sundaram M, Sivaprasadarao A, Findlay JB. Expression and mutagenesis of retinol-binding protein. Methods Mol Biol 1998;89:141-53.
  • West CE. Meeting requirements for vitamin A. Nutr Rev 2000 Nov;58(11):341-5.
  • Whiting SJ, Lemke B. Excess retinol intake may explain the high incidence of osteoporosis in northern Europe. Nutr Rev 1999 Jun;57(6):192-5.
  • Wolf G. Release of stored retinol from adipocytes. Nutr Rev 1998 Jan;56(1 Pt 1):29-30.
  • Zhang D, Holmes WF, Wu S, et al. Retinoids and ovarian cancer. J Cell Physiol 2000 Oct;185(1):1-20.

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This page was updated on: 2003-12-11 20:16:43

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