Vitamin A and Carotenoids
Vitamin A is actually a family of fat-soluble vitamins. Retinol is one of the most active, or usable, forms of vitamin A, and is found in animal foods such as liver and eggs. It can be converted to retinal and retinoic acid, other active forms of the vitamin A family. Some plant foods contain orange pigments called provitamin A carotenoids that the liver can convert to retinol. Beta-carotene is a provitamin A carotenoid found in many foods. Lycopene, lutein, and zeaxanthin are also carotenoids commonly found in food, but your body cannot convert them to vitamin A.
What does Vitamin A do?
Vitamin A plays an important role in vision, bone growth, reproduction, cell division and differentiation. It maintains the surface linings of your eye and your respiratory, urinary, and intestinal tracts. When those linings break down, bacteria can enter your body and cause infection. The immune system helps prevent or fight off infections by making white blood cells that destroy harmful bacteria and viruses. Vitamin A may help lymphocytes, a type of white blood cell that fights infections, function more effectively. Vitamin A also may help prevent bacteria and viruses from entering your body by maintaining the integrity of skin and mucous membranes.
Some carotenoids, in addition to serving as a source of vitamin A, have been shown to function as antioxidants in laboratory tests. However, this role has not been consistently demonstrated in humans. Antioxidants protect cells from free radicals, which are potentially damaging by-products of the body's metabolism that may contribute to the development of some chronic diseases.
What foods provide Vitamin A?
Whole eggs, whole milk, and liver are among the few foods that naturally contain vitamin A. Vitamin A is present in the fat portion of whole milk, so it is not found in fat-free milk. Most fat-free milk and dried nonfat milk solids sold in the US are fortified with vitamin A. There are many other fortified foods such as breakfast cereals that also provide vitamin A. Some of the best food sources of Vitamin A and provitamin A carotenoids are listed at the end of this article. It is important to regularly eat foods that provide vitamin A or beta-carotene even though your body can store vitamin A in the liver. Stored vitamin A will help meet your needs when your intake from food is low.
How much Vitamin A do we need?
The Recommended Dietary Allowance (RDA) is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97-98%) healthy individuals in each life-stage and gender group. The 1989 RDAs for vitamin A for adults are: 1000 IU (International Units) for men, and 4000 IU for women including pregnant and breastfeeding women.
RDAs for children are: 2000 IU for 1-3 year olds, 2500 IU for 4-6 year olds, and 3500 for 7-10 year olds. Adult RDA's apply starting at age 11. Large surveys of American nutritional status and eating habits suggest that the diets of as many as 25% of Americans do not provide the recommended RDA's.
There is no separate RDA for beta-carotene or other carotenoids. A recent study by the Institute of Medicine (part of the US National Academy of Sciences) suggests that consuming 3 to 6 mg of beta-carotene daily will maintain plasma B-carotene blood levels in the range associated with a lower risk of chronic diseases. This concentration can be achieved by a diet that provides five or more servings of fruits and vegetables per day.
When can vitamin A deficiency occur?
Vitamin A deficiency is rare in the US, but it is still a major public health problem in the developing world. It is most often associated with protein/calorie malnutrition and affects over 120 million children worldwide. It is also a leading cause of childhood blindness. In countries where immunization programs are not widespread and vitamin A deficiency is common, millions of children die each year from complications of infectious diseases such as measles.
Signs of vitamin A deficiency include night blindness, dry skin, and decreased resistance to infections. In ancient Egypt it was known that night blindness could be cured after eating liver, which was later found to be a rich source of vitamin A. Vitamin A deficiency contributes to blindness by making the eye very dry, damaging the cornea of the eye (called xerophthalmia), and promoting damage to the retina of the eye. Extremely dry skin, dry hair, sloughing off of skin, and broken fingernails are other common signs of vitamin A deficiency. Vitamin A deficiency also decreases resistance to infections, and may contribute to the pneumonia associated with vitamin A deficiency.
There is increased interest in subclinical forms of vitamin A deficiency, described as low storage levels of vitamin A that do not cause overt deficiency symptoms. This mild degree of vitamin A deficiency may increase children's risk of developing respiratory and diarrheal infections, decrease their growth rate, slow bone development, and decrease their likelihood of survival from serious illness.
Children living 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, intestines, or with inadequate fat digestion/absorption.
As a result of the worldwide significance of vitamin A deficiency in children, the World Health Organization and the United Nations International Children's Emergency 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 supplementation for children 6 to 24 months of age hospitalized with measles, and for hospitalized children older than 6 months who are considered to be at high-risk for subclinical vitamin A deficiency.
Who may need extra vitamin A to prevent a deficiency?
Children with low body stores of vitamin A who have measles may require vitamin A supplementation, as discussed above. Individuals with chronic fat malabsorption also poorly absorb vitamin A. Fat malabsorption can occur with cystic fibrosis, sprue, pancreatic disorders, and after stomach surgery. Healthy adults usually have a one-year reserve of vitamin A stored in their livers and should not be at risk of deficiency during periods of short term fat malabsorption. Long term problems absorbing fat, however, can result in deficiency and may require vitamin A supplementation. Children may only have enough stores of vitamin A to last several weeks, so children with fat malabsorption may require immediate vitamin A supplementation.
What is the association between vitamin A, beta carotene and cancer?
Surveys suggest an association between diets rich in beta-carotene and vitamin A and a lower risk of many types of cancer, and there is evidence that higher intake of green and yellow vegetables or food sources of beta-carotene and/or vitamin A decreased the risk of lung cancer.
But recent intervention studies have not supported a protective role for beta-carotene in cancer prevention. In a study of 29,000 men, incidence of lung cancer was greater in the group of smokers who took a daily supplement of beta-carotene. The Carotene and Retinol Efficacy Trial, a lung cancer chemoprevention trial that provided randomized subjects with supplements of beta carotene and vitamin A, was stopped after researchers discovered that subjects receiving beta carotene had a 46% higher risk of dying from lung cancer. There may be a relationship between alcohol and beta-carotene. In this study only the men who consumed two or more drinks a day showed an adverse response to beta-carotene supplementation.
The Institute of Medicine has stated that beta-carotene supplements are not recommended for routine use by the general population, but that they may have a role in the prevention of vitamin A deficiency in populations with inadequate vitamin A intake.
What is the health risk of too much vitamin A?
Hypervitaminosis A refers to high storage levels of vitamin A in the body that can lead to toxic symptoms. Toxicity can result in dry, itchy skin, headache, fatigue, hair loss, loss of appetite, vomiting, and liver damage. When toxic symptoms arise suddenly, which can happen after consuming very large amounts of vitamin A over a short period of time, signs of toxicity include dizziness, blurred vision, and muscular uncoordination. Most cases of vitamin A toxicity result from an excess intake of vitamin A in supplements. A generally recognized safe upper limit of intake for vitamin A from diet and supplements is 8,000 to 10,000 IU per day.
Vitamin A toxicity also can cause severe birth defects. Women of child-bearing age are advised to limit their total daily intake of vitamin A (retinol) from foods and supplements combined to no more than 8,000 IU per day.
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. Isotretinoin (sold as Roaccutane or Accutane) is considered an effective anti-acne therapy, but at very high doses it can be toxic, which is why this medication is usually saved for the most severe forms of acne. 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 is the health risk of too many carotenoids?
Provitamin A carotenoids such as beta-carotene are generally considered safe because they are not traditionally associated with specific adverse health effects. The conversion of provitamin A carotenoids from plant foods to vitamin A slows down when body has adequate stores of Vitamin A, so the levels are naturally limited. A high intake of provitamin A carotenoids (from food sources) can turn your skin yellow, but this is not considered dangerous to health.
As mentioned above, the evidence on benefits and adverse effects of taking beta-carotene supplements is contradictory, and the potential health risks are not well understood. The lung cancer trial suggested a greater incidence of lung cancer and total mortality in smokers who supplemented their diet with 20 mg of beta-carotene per day. But the Physicians' Health Study compared the effects of taking 50 mg of beta-carotene every other day to a placebo (sugar pill) in 22,000 male physicians, and found no adverse health effects. A study in China tested the ability of four different nutrient combinations to inhibit the development of esophageal and gastric cancers in 30,000 men and women. This study suggested a beneficial role for beta-carotene: after 5 years the participants who took a combination of beta-carotene, selenium and vitamin E had a 13% reduction in cancer deaths. At this time, taking beta-carotene supplements is not recommended.
Food Sources of Vitamin A
The following lists include some of the foods which are good dietary sources of vitamin A and provitamin A carotenoids. The best sources are liver, eggs and fortified milk, many orange fruits and green vegetables. Food manufacturers fortify a wide range of products with Vitamin A. Breakfast cereals, pastries, breads, crackers, cereal grain bars and other foods may be fortified with 10% to 15% of the recommended daily amount for Vitamin A. Read the nutrition facts panel of the food label to determine whether a food provides Vitamin A.
Some animal food sources of Vitamin A
- Beef liver, 3 oz.: 30,325 IU -- 610% of the recommended daily amount
- Chicken liver, 3 oz.: 13,920 IU
- Egg substitute, fortified, 1/4 c: 1355 IU
- Fat free milk, fortified w/ vitamin A, 1 c: 500 IU
- Cheese pizza, 1/8 of a 12" diameter: 380 IU
- Cheddar cheese, 1 oz: 300 IU
- 1 Egg, medium: 280 IU
Some plant food sources of Vitamin A (from beta-carotene)
- 1 raw carrot, 7-8 inches long: 20,250 IU -- 410% of the recommended daily amount
- Carrots, boiled, 1/2 c: 19,150 IU
- 1 Mango, uncooked: 8,050 IU
- Spinach, boiled, 1/2 c: 7,370 IU
- Cantaloupe, raw, 1 c cubes: 5,160 IU
- Kale, boiled, 1/2 c: 4,810
- Red Pepper (sweet) raw: 1/2 c sliced: 2,620 IU
- 1 packet of instant Oatmeal (fortified): 1,050 IU
- Medium sized peach: 525 IU
Information provided by
National Institutes of Health
Article Created: 2001-01-29
Article Updated: 2001-10-16
Each year, Medical College of Wisconsin physicians care for more than 180,000 patients, representing nearly 500,000 patient visits. Medical College physicians practice at Children's Hospital of Wisconsin, Froedtert Memorial Lutheran Hospital, the Milwaukee VA Medical Center, and many other hospitals and clinics in Milwaukee and southeastern Wisconsin.
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