Vitamin A

Other name(s):

b-carotene, beta-carotene, retinol, vitamin A-1

General description

Vitamin A is also called retinol. It was the first substance isolated in the group called vitamins. It is 1 of 4 fat-soluble vitamins. This means it can dissolve in fats and oils. It’s found in animal products. Fat-soluble vitamins are stored in the body. They can build up to toxic levels if you take too much of them.

Precursors of vitamin A exist in plants. They’re called carotenoids. These are fat soluble but nontoxic, even in large quantities. The best-known carotenoid is beta-carotene. Both retinoids and carotenoids are good antioxidants.

Vitamin A is part of the reproductive process. It helps with the growth of sperm. It also helps with the growth of a baby in the womb. But high doses of vitamin A and synthetic retinols may lead to problems with growth in the womb. It may also lead to birth defects. Vitamin A seems to help the growing tissues in a baby in the womb. It also helps the placenta form during pregnancy.

Vitamin A is an important factor in growth throughout life. Vitamin A helps grow and maintain epithelial tissues. These include mucous membranes, the lining of the gastrointestinal tract, lungs, bladder, urinary tract, vagina, cornea, and skin. Vitamin A also helps the growth of bones and teeth.

Vitamin A prevents drying of the skin. This may protect the body from infectious diseases. It also helps maintain the immune system.

Vitamin A is also needed for night vision. Retinol (a vitamin A metabolite) combines with opsin (a pigment in the retina of the eye) to form rhodopsin. This is a chemical that helps with night vision.

Medically valid uses

Vitamin A helps with the reproductive process, growth, and development. It also keeps eyes and skin healthy and acts as an antioxidant.

Vitamin A supplements may reduce the risk for certain types of cancer. Vitamin A influences cell development. It also increases the activity of immune-system cells. This could make it valuable in the fight against cancer, especially skin, lung, bladder, and breast cancer.

Unproven claims

There may be benefits that have not yet been proven through research.

Vitamin A may prevent some types of cancer and acne. It may also help treat psoriasis. It’s also claimed to help treat dry or wrinkled skin. It may also protect against the effects of pollution and prevent respiratory tract infections. Vitamin A may aid in healing sunburns. It’s also been used to treat kidney stones, inflammatory bowel disease, and deafness.

Vitamin A has been called the anti-infection vitamin because of its role in helping the body fight bacterial, parasitic, and viral infections.

Recommended intake

Vitamin A is measured in Retinol Activity Equivalents (RAE) to account for the different bioactivities of retinol and provitamin A carotenoids. The RDA is the recommended dietary allowance.

Vitamin A was previously listed on labels in international units (IUs). Under new FDA labeling rules, vitamin A will be listed in mcg RAE and not IUs. This change took effect in 2020 and 2021. An RAE can't be directly converted into an IU if you don't know the source of vitamin A. Conversion rates between mcg RAE and IU are:

• 1 IU retinol = 0.3 mcg RAE

• 1 IU beta-carotene from dietary supplements = 0.15 mcg RAE

• 1 IU beta-carotene from food = 0.05 mcg RAE

• 1 IU alpha-carotene or beta-cryptoxanthin = 0.025 mcg RAE

*Adequate intake (AI). This is based on the average intake in healthy, breastfed infants.

Smaller people need less vitamin A than larger people do. In most cases, women need less than men, except during pregnancy and while breastfeeding.

Vitamin A is stable at room temperature. It doesn’t need to be refrigerated. Cooking, freezing, or canning vegetables and fruits doesn’t destroy much vitamin A. But you shouldn’t freeze vitamin A tablets and capsules. Vitamin A is also stable in light.

A poor diet with not enough vitamin A can increase your need for vitamin A. So can diets containing large amounts of snack foods containing the fat substitute olestra.

Malabsorption syndromes that cause excess fat in the stool (steatorrhea) may deplete all 4 fat-soluble vitamins: A, D, E, and K. There are many types of malabsorption syndromes. These include:

• Lactose intolerance

• Tropical and nontropical sprue

• Celiac disease

• Cystic fibrosis

• Ulcerative colitis

• Crohn's disease

Steatorrhea can also be caused by removal of all or part of the pancreas.

You may need more vitamin A if you have any of these:

• A fever that lasts

• Hyperthermia

• Infection

• Ongoing use of mineral oil

• Diabetes

• Hyperthyroidism

An early sign of vitamin A deficiency is night blindness. This may start with less ability to see at night or in the dark. The time for your eyes to adjust to the dark increases. Over time, you lose the ability to see at night.

Vitamin A deficiency also causes conjunctival dryness. This starts with a dry feeling in your eyes. The eyelid linings also become dry and rough. Then the cornea dries out. It becomes wrinkled and cloudy. Scarring then occurs. This causes permanent changes. It leads to blindness.

Skin changes are another sign of too little vitamin A. The skin becomes dry and rough. This is seen over the shoulders, buttocks, and the opposite side of a joint of the arms and legs. Little bumps may show up around the base of each hair. This causes a sandpaper-like feel to the skin.

Mucous membranes may also change. This may affect the lining of the urinary tract. This may cause burning and bleeding with urination. The lining of the vagina may also get dry and inflamed.

Retinol is used to treat vitamin A deficiency. In many undeveloped countries, vitamin A deficiency is common. Because vitamin A can be stored in the body, large doses can be given to children (and some adults) only 2 or 3 times a year. This is done to prevent xerophthalmia. This is a condition that leads to blindness. Vitamin A deficiency is rare in the U.S. When it occurs, it’s usually due to malabsorption caused by other diseases.

Side effects, toxicity, and interactions

Vitamin A in the form of beta-carotene is considered safe. It doesn’t appear to be toxic in large doses. But high doses over a long period of time can lead to carotenemia. In this condition, your skin becomes yellowish orange.

Too much vitamin A may increase the risk for hip fracture in women.

Vitamin A overdose in the form of retinoids from animal sources can be toxic. The conditions of overdose (hypervitaminosis) are divided into two groups: acute and chronic. These are then split into infant and adult.

Children are more sensitive than adults to overdoses of vitamin A. The symptoms of an acute overdose in an infant or child include:

• Nausea and vomiting

• Drowsiness

• Extreme sleepiness

• Bulging soft spot (fontanel) on the top of the baby's head

• Pseudotumor cerebri. This condition increases pressure around the brain, bulging of the optic disc in the back of the eye, paralysis, or change in function of some of the cranial nerves. This is seen after the soft spot has closed over and the sutures fused.

The symptoms of a chronic overdose in a baby or child include:

• Loss of appetite

• Itching

• Slowed weight gain

• Irritability

• Hair loss (alopecia)

• Bone pain

• Swelling

• Skin changes, such as dryness, roughness, and cracks in the corners of the mouth

In adults, symptoms of an acute overdose may include:

• Headache

• Nausea and vomiting

• Irritability

• Seizures

• Double vision

The signs of a chronic overdose in adults include:

• Skin changes, such as dryness, roughness, and cracks in the lips and corners of the mouth

• Hair loss

• Loss of appetite

• Increased pressure around the brain that may cause symptoms like a brain tumor

You shouldn’t take vitamin A supplements if you’re allergic to vitamin A.

You shouldn’t take very high doses of vitamin A during pregnancy. This is because high doses may cause malformations in your baby growing in the womb.

Mineral oil, cholestyramine, and foods containing olestra may interfere with the absorption of vitamin A. Orlistat, a medicine for weight loss, has been shown to decrease absorption of beta-carotene and vitamin E. Whether orlistat has the same effect on vitamin A is unknown.

You shouldn’t take vitamin A supplements if you’re taking isotretinoin, acitretin, or etretinate.

If you’re using topical ointments that are in the retinoid family, ask your healthcare provider if it’s safe for you to take vitamin A supplements.

Taking tetracycline with high doses of vitamin A may cause benign intracranial hypertension. You shouldn’t take this medicine with vitamin A.

Oral birth control pills increase the levels of vitamin A in your body. For this reason, you may not need vitamin A supplements.

Warfarin (Coumadin) is used to slow blood clotting. Large amounts of vitamin A can also slow blood clotting. Taking vitamin A along with warfarin can increase the chances of bruising and bleeding. Have your blood checked regularly. The dose of your warfarin might need to be changed.