Vitamins are substances that your body needs to grow and develop normally. Vitamin A plays a role in your

• Vision
• Bone growth
• Reproduction
• Cell functions
• Immune system

Vitamin A is an antioxidant. It can come from plant or animal sources. Plant sources include colorful fruits and vegetables. Animal sources include liver and whole milk. Vitamin A is also added to foods like cereals.

Vegetarians, young children, and alcoholics may need extra Vitamin A. You might also need more if you have certain conditions, such as liver diseases, cystic fibrosis, and Crohn's disease. Check with your health care provider to see if you need to take vitamin A supplements.

Vitamin A is a fat-soluble vitamin that is naturally present in many foods. Vitamin A is important for normal vision, the immune system, and reproduction. Vitamin A also helps the heart, lungs, kidneys, and other organs work properly.

There are two different types of vitamin A. The first type, preformed vitamin A, is found in meat, poultry, fish, and dairy products. The second type, provitamin A, is found in fruits, vegetables, and other plant-based products. The most common type of provitamin A in foods and dietary supplements is beta-carotene.

Vitamin A, along with other vitamins, minerals and other compounds, is an essential micronutrient. This means that our bodies cannot manufacture it and therefore it has to be included in our diet.

Vitamin A from food is stored in the liver until required by the body and is bound to protein before being transported to where it is needed.

Vitamin A is essential for many physiological processes, including maintaining the integrity and function of all surface tissues (epithelia): for example, the skin, the lining of the respiratory tract, the gut, the bladder, the inner ear and the eye. Vitamin A supports the daily replacement of skin cells and ensures that tissues such as the conjunctiva are able to produce mucous and provide a barrier to infection. Vitamin A is also essential for vision under conditions of poor lighting, for maintaining a healthy immune system, for growth and development and for reproduction. Vitamin A supports many systems in the body. For this reason, vitamin A deficiency is now referred to as vitamin A deficiency disorders. For simplicity, however, we will continue to use the older term vitamin A deficiency (VAD).

One of the main consequences of VAD is an increased risk of severe infection. Infection increases the body's demand for vitamin A and so the deficiency gets worse. Children can therefore become involved in a vicious cycle of deficiency and infection, which is why vitamin A deficiency is such an important cause of child mortality.

Sources of vitamin A

There are two main sources of vitamin A: animal sources and plant sources. All the sources of vitamin A need some fat in the diet to aid absorption.

In animal sources, vitamin A is found as retinol, the ‘active’ form of vitamin A. Liver, including fish liver, is a very good source. Other animal sources are egg yolk (not the white) and dairy products such as milk (including human breast milk), cheese and butter. Meat, from the animal's muscles, is not a good source.

Plant sources contain vitamin A in the form of carotenoids which have to be converted during digestion into retinol before the body can use it. Carotenoids are the pigments that give plants their green colour and some fruits and vegetables their red or orange colour.

Plant sources of vitamin A include: mangos, papaya, many of the squashes, carrots, sweet potatoes and maize (but not the white varieties). Other good sources of vitamin A are red palm oil and biruti palm oil. (Note: if these oils are boiled to remove their colour the vitamin A is destroyed.)

Some fruits and vegetables are easier to digest than others, and it has been shown that dark green leafy vegetables such as spinach or amaranth are harder to digest. Mashing these vegetables up after cooking makes them easier to digest. When mashed they can be added to staples, which also makes them easier to disguise – children the world over do not like green vegetables!

It is important that all sources of vitamin A are not overcooked, as this can reduce the vitamin A content. Ultraviolet light can also reduce the vitamin A content of food, so drying of fruits such as mangos should not be done in direct sunlight.

Diets that rely heavily on local carbohydrates, such as rice, fufu, ugali, cassava, millet and sorghum, are very low in vitamin A, unless vitamin A-rich foods are added.

Food sources of vitamin A

Fruits and vegetables

Dark green leafy vegetables, for example amaranth (red or green), spinach and chard

Orange-fleshed sweet potatoes

Carrots

Squashes/pumpkins

Yellow maize

Mangoes

Papayas

Animal sources

Liver, eggs, milk (including breast milk)

Oils

Red palm oil or biruti palm oil

How much vitamin A does a child need?

Because children are growing, they need a relatively high intake of vitamin A; about half as much as an adult. Another reason for the relatively high intake is because children are prone to infection which increases the metabolic rate and hence the rate at which they use vitamin A.

Breast milk contains enough vitamin A for children up to six months of age, but after that complementary foods (the foods given in addition to breast milk) should include small amounts of vitamin A-rich foods.

For a young child, a balanced diet that is rich in vitamin A should include helpings of at least 2–3 vitamin A-rich fruits and vegetables a day, plus a little bit of fat to aid absorption.

Young children are totally dependent on their mother or other carers for their diet, and so it is vital that mothers and carers of young children know what constitutes a healthy diet for their child.

The amount of vitamin A you need depends on your age and sex. Average daily recommended amounts are listed below in micrograms (mcg) of retinol activity equivalents (RAE).

Vitamin A is found naturally in many foods and is added to some foods, such as milk and cereal. You can get recommended amounts of vitamin A by eating a variety of foods, including the following:

• Beef liver and other organ meats (but these foods are also high in cholesterol, so limit the amount you eat).
• Some types of fish, such as salmon.
• Green leafy vegetables and other green, orange, and yellow vegetables, such as broccoli, carrots, and squash.
• Fruits, including cantaloupe, apricots, and mangos.
• Dairy products, which are among the major sources of vitamin A for Americans.
• Fortified breakfast cereals.

Vitamin A is available in dietary supplements, usually in the form of retinyl acetate or retinyl palmitate (preformed vitamin A), beta-carotene (provitamin A), or a combination of preformed and provitamin A. Most multivitamin-mineral supplements contain vitamin A. Dietary supplements that contain only vitamin A are also available.

Most people in the United States get enough vitamin A from the foods they eat, and vitamin A deficiency is rare. However, certain groups of people are more likely than others to have trouble getting enough vitamin A:

• Premature infants, who often have low levels of vitamin A in their first year.
• Infants, young children, pregnant women, and breastfeeding women in developing countries.
• People with cystic fibrosis.

Vitamin A deficiency is rare in the United States, although it is common in many developing countries. The most common symptom of vitamin A deficiency in young children and pregnant women is an eye condition called xerophthalmia. Xerophthalmia is the inability to see in low light, and it can lead to blindness if it isn't treated.

Scientists are studying vitamin A to understand how it affects health. Here are some examples of what this research has shown.

Cancer

People who eat a lot of foods containing beta-carotene might have a lower risk of certain kinds of cancer, such as lung cancer or prostate cancer. But studies to date have not shown that vitamin A or beta-carotene supplements can help prevent cancer or lower the chances of dying from this disease. In fact, studies show that smokers who take high doses of beta-carotene supplements have an increased risk of lung cancer.

Age-Related Macular Degeneration

Age-related macular degeneration (AMD), or the loss of central vision as people age, is one of the most common causes of vision loss in older people. Among people with AMD who are at high risk of developing advanced AMD, a supplement containing antioxidants, zinc, and copper with or without beta-carotene has shown promise for slowing down the rate of vision loss.

Measles

When children with vitamin A deficiency (which is rare in North America) get measles, the disease tends to be more severe. In these children, taking supplements with high doses of vitamin A can shorten the fever and diarrhea caused by measles. These supplements can also lower the risk of death in children with measles who live in developing countries where vitamin A deficiency is common.

What Is Vitamin A?

Vitamin A is a family of compounds that play an important role in vision, bone growth, reproduction, cell division, and cell differentiation. We get vitamin A from a variety of sources. Two of the most common sources are retinol and beta-carotene.

Retinol is sometimes called “true” vitamin A because it is nearly ready for the body to use. Retinol is found in such animal foods as liver, eggs, and fatty fish. It also can be found in many fortified foods, such as breakfast cereals, and in dietary supplements.

Beta-carotene is a precursor for vitamin A. The body needs to convert it to retinol or vitamin A for use. Beta-carotene is found naturally in mostly orange and dark green plant foods, such as carrots, sweet potatoes, mangos, and kale.

The body stores both retinol and beta-carotene in the liver, drawing on this store whenever more vitamin A is needed.

How Much Vitamin A Do I Need?

The Institute of Medicine developed the Recommended Dietary Allowance (RDA) for vitamin A (retinol). The recommended intakes are listed in International Units (IU) in the table, below:

The body can convert beta-carotene into vitamin A to help meet these requirements. Although there is no RDA for beta-carotene, the National Institutes of Health (NIH) Office of Dietary Supplements recommends eating five or more servings of fruits and vegetables per day, including dark green and leafy vegetables and deep yellow or orange fruits to get appropriate amounts of beta-carotene.

How Does Vitamin A Affect My Bones?

Vitamin A is a family of fat-soluble compounds that play an important role in vision, bone growth, reproduction, cell division, and cell differentiation. Vitamin A is important for healthy bones. However, too much vitamin A has been linked to bone loss and an increase in the risk of hip fracture. Scientists believe that excessive amounts of vitamin A trigger an increase in osteoclasts, the cells that break down bone. They also believe that too much vitamin A may interfere with vitamin D, which plays an important role in preserving bone.

Retinol is the form of vitamin A that causes concern. In addition to getting retinol from their diets, some people may be using synthetic retinoid preparations that are chemically similar to vitamin A to treat acne, psoriasis, and other skin conditions. These preparations have been shown to have the same negative impact on bone health as dietary retinol. Use of these medications in children and teens also has been linked to delays in growth.

Beta-carotene, on the other hand, is largely considered to be safe and has not been linked to adverse effects in bone or elsewhere in the body.

How Can I Make Sure I Get the Right Amount of Vitamin A?

Surveys suggest that most Americans are getting adequate amounts of vitamin A. The Institute of Medicine cautions against daily intakes of retinol above 10,000 IU.

The chart below identifies some common food sources of retinol. Most of the reported cases of vitamin A toxicity have been blamed on the use of supplements. Healthy individuals who eat a balanced diet generally do not need a vitamin A supplement.

Plant sources of beta-carotene are not as well absorbed as the animal sources of vitamin A listed in the chart, but they are still an important source of this vitamin. Dark orange and green vegetables and fruit, including carrots, sweet potatoes, spinach, cantaloupe, and kale are excellent sources of beta-carotene. Because of concerns about the negative effects of too much retinol, some people prefer to eat more foods rich in beta-carotene to satisfy their need for vitamin A.

Are Some People at Special Risk of Getting Too Much Vitamin A?

The 1988–94 National Health and Nutrition Examination Survey (NHANES III) found high levels of retinol in 5 to 10 percent of the survey participants. Increased levels were more common in men age 30 and older and in women age 50 and older.

Older people who regularly take dietary supplements containing vitamin A may be at higher risk of getting too much vitamin A.

Studies suggest that taking dietary supplements is a common practice among many older adults. However, the routine use of vitamin A supplements, as well as fortified foods, in older men and women is increasingly being questioned. Older adults are at significant risk for osteoporosis and related fractures, and their serum (blood) levels of retinol increase with age. As a result, fortified foods and supplements containing vitamin A in the form of beta-carotene may be a better choice for bone health in this population.

The supplement label provides information about how much vitamin A is provided, in both International Units and as a percentage of the RDA. The list of ingredients will contain information about which forms of vitamin A are included. Other names for retinol include retinyl, palmitate, and retinyl acetate.

Yes, high intakes of some forms of vitamin A can be harmful.

Getting too much preformed vitamin A (usually from supplements or certain medicines) can cause dizziness, nausea, headaches, coma, and even death. High intakes of preformed vitamin A in pregnant women can also cause birth defects in their babies. Women who might be pregnant should not take high doses of vitamin A supplements.

Consuming high amounts of beta-carotene or other forms of provitamin A can turn the skin yellow-orange, but this condition is harmless. High intakes of beta-carotene do not cause birth defects or the other more serious effects caused by getting too much preformed vitamin A.

The daily upper limits for preformed vitamin A include intakes from all sources—food, beverages, and supplements—and are listed below. These levels do not apply to people who are taking vitamin A for medical reasons under the care of a doctor. Upper limits for beta-carotene and other forms of provitamin A have not been established.

Yes, vitamin A supplements can interact or interfere with medicines you take. Here are several examples:

• Orlistat (Alli®, Xenical®), a weight-loss drug, can decrease the absorption of vitamin A, causing low blood levels in some people.
• Several synthetic forms of vitamin A are used in prescription medicines. Examples are the psoriasis treatment acitretin (Soriatane®) and bexarotene (Targretin®), used to treat the skin effects of T-cell lymphoma. Taking these medicines in combination with a vitamin A supplement can cause dangerously high levels of vitamin A in the blood.

Tell your doctor, pharmacist, and other healthcare providers about any dietary supplements and medicines you take. They can tell you if those dietary supplements might interact or interfere with your prescription or over-the-counter medicines or if the medicines might interfere with how your body absorbs, uses, or breaks down nutrients.