NutritionSupplement.net

Vitamin A (or Vitamin A Retinol, retinal, and four carotenoids including beta carotene) is a vitamin that is needed by the retina of the eye in the form of a specific metabolite, the light-absorbing molecule retinal, that is absolutely necessary for both low-light (scotopic vision) and color vision. Vitamin A also functions in a very different role, as an irreversibly oxidized form of retinol known as retinoic acid, which is an important hormone-like growth factor for epithelial and other cells.

In foods of animal origin, the major form of vitamin A is an ester, primarily retinyl palmitate, which is converted to the retinol (chemically an alcohol) in the small intestine. The retinol form functions as a storage form of the vitamin, and can be converted to and from its visually active aldehyde form, retinal. The associated acid (retinoic acid), a metabolite that can be irreversibly synthesized from vitamin A, has only partial vitamin A activity, and does not function in the retina for the visual cycle.

What is it?

Vitamin A is a vitamin. It can be found in many fruits, vegetables, eggs, whole milk, butter, fortified margarine, meat, and oily saltwater fish. It can also be made in a laboratory.

Vitamin A is used for treating vitamin A deficiency. It is also used to reduce complications of diseases such as malaria, HIV, measles, and diarrhea in children with vitamin A deficiency.

Women use vitamin A for heavy menstrual periods, premenstrual syndrome (PMS), vaginal infections, yeast infections, “lumpy breasts” (fibrocystic breast disease), and to prevent breast cancer. Some women with HIV use vitamin A to decrease the risk of transmitting HIV to the baby during pregnancy, childbirth, or breast-feeding.

Men use vitamin A to raise their sperm count.

Some people use vitamin A for improving vision and treating eye disorders including age-related macular degeneration (AMD), glaucoma, and cataracts.

Vitamin A is also used for skin conditions including acne, eczema, psoriasis, cold sores, wounds, burns, sunburn, keratosis follicularis (Darier’s disease), ichthyosis (noninflammatory skin scaling), lichen planus pigmentosus, and pityriasis rubra pilaris.

It is also used for gastrointestinal ulcers, Crohn’s disease, gum disease, diabetes, Hurler syndrome (mucopolysaccharidosis), sinus infections, hayfever, and urinary tract infections (UTIs).

Vitamin A is also used for shigellosis, diseases of the nervous system, nose infections, loss of sense of smell, asthma, persistent headaches, kidney stones, overactive thyroid, iron-poor blood (anemia), deafness, ringing in the ears, and precancerous mouth sores (leukoplakia).

Other uses include preventing and treating cancer, protecting the heart and cardiovascular system, slowing the aging process, and boosting the immune system.

Vitamin A is applied to the skin to improve wound healing, reduce wrinkles, and to protect the skin against UV radiation.

How effective is it?

Natural Medicines Comprehensive Database rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, Ineffective, and Insufficient Evidence to Rate.

The effectiveness ratings for VITAMIN A are as follows:

Effective for...

* Treatment and prevention of vitamin A deficiency. Vitamin A deficiency can occur in people with protein deficiency, diabetes, over-active thyroid, fever, liver disease, cystic fibrosis, or an inherited disorder called abetalipoproteinemia.

Possibly effective for...

* Preventing breast cancer. Women who have not passed menopause and who get high levels of vitamin A from their diet seem to be at lower risk of getting breast cancer than other women. It’s not known whether taking vitamin A supplements has the same benefit.
* Reducing complications of diseases such as malaria, HIV, measles, and diarrhea in children with vitamin A deficiency.
* Reducing problems during pregnancy and after giving birth in underfed (malnourished) women.
* Prevention of cataracts.
* Improving recovery from laser eye surgery when used in combination with vitamin E.

Possibly ineffective for...

* Reducing fetal and early infant death in children born to women with nutrition problems.
* Iron-poor blood (anemia).
* Decreasing the risk of HIV transmission during pregnancy, delivery, and breast-feeding.
* Reducing side effects of chemotherapy in children.

Likely ineffective for...

* Reducing the risk of tumors in the head and neck.
* Treating pneumonia in children living in poor countries.

Insufficient evidence to rate effectiveness for...

* Lung cancer. Limited research suggests that taking vitamin A by mouth might improve survival and reduce the development of new tumors in people with lung cancer.
* Ovarian cancer. Population research suggests that taking vitamin A doesn’t affect the risk of developing ovarian cancer.
* Cervical cancer. Preliminary clinical research suggests that a specific form of vitamin A, 13-cis-retinoic acid, taken by mouth might improve precancerous changes in the cervix of women with human papillomavirus (HPV) infection.
* Esophageal cancer. Taking vitamin A in combination with beta-carotene does not seem to prevent esophageal cancer.
* Pancreatic cancer. Taking vitamin A in combination with beta-carotene does not seem to prevent pancreatic cancer.
* Colorectal cancer. Taking vitamin A in combination with beta-carotene does not seem to prevent colorectal cancer.
* Stomach cancer. Taking vitamin A in combination with beta-carotene does not seem to prevent stomach cancer.
* Promoting good vision.
* Age-related macular degeneration (AMD).
* Glaucoma.
* Preventing and speeding recovery from infections.
* Improving immune function.
* Skin conditions other than acne.
* Relieving hay fever symptoms.
* Other conditions.

More evidence is needed to rate vitamin A for these uses.

How does it work?

Vitamin A is required for the proper development and functioning of our eyes, skin, immune system, and many other parts of our bodies.

Are there safety concerns?

Vitamin A is LIKELY SAFE for most people when taken by mouth in amounts less than 10,000 units per day.

Some scientific research suggests that higher doses might increase the risk of osteoporosis and hip fracture, particularly in older people. Adults who eat low-fat dairy products, which are fortified with vitamin A, and a lot of fruits and vegetables usually don’t need vitamin A supplements or multivitamins that contain vitamin A.

Long-term use of large amounts of vitamin A might cause serious side effects including fatigue, irritability, mental changes, anorexia, stomach discomfort, nausea, vomiting, mild fever, excessive sweating, and many other side effects. In women who have passed menopause, taking too much vitamin A can increase the risk of osteoporosis and hip fracture.

There is growing concern that taking high doses of antioxidant supplements such as vitamin A might do more harm than good. Some research shows that taking high doses of vitamin A supplements might increase the chance of death from all causes and possibly other serious side effects.

Vitamin A is likely safe for children when taken in the recommended amounts. When amounts greater than those recommended are taken, side effects can include irritability, sleepiness, vomiting, diarrhea, loss of consciousness, headache, vision problems, peeling skin, increased risk of pneumonia and diarrhea, and other problems. The maximum amounts of vitamin A that are safe for children are based on age:

* Less than 2000 units/day in children up to 3 years old.
* Less than 3000 units/day in children ages 4 to 8 years old.
* Less than 5700 units/day in children ages 9 to 13 years old.
* Less than 9300 units/day in children ages 14 to 18 years old.

Special precautions & warnings:
Pregnancy and breast-feeding: Vitamin A is LIKELY SAFE for pregnant or breast-feeding women when taken in recommended amounts of less than 10,000 units per day. Larger amounts are POSSIBLY UNSAFE. Vitamin A can cause birth defects. It’s especially important for pregnant women to monitor their intake of vitamin A from all sources during the first three months of pregnancy. Forms of vitamin A are found in several foods including animal products, primarily liver, some fortified breakfast cereals, and dietary supplements.

Excessive use of alcohol: Drinking alcohol may increase vitamin A’s potentially harmful effects on the liver.

A type of high cholesterol called "Type V hyperlipoproteinemia:" This condition might increase the chance of vitamin A poisoning. Don’t take vitamin A if you have this condition.

Liver disease: Too much vitamin A might make liver disease worse. Don’t take vitamin A if you have liver disease.

Are there interactions with medications?

Medications for skin conditions (Retinoids)
Some medications for skin conditions have vitamin A effects. Taking vitamin A pills and these medications for skin conditions could cause too much vitamin A effects and side effects.

Moderate
Be cautious with this combination.

Antibiotics (Tetracycline antibiotics)
Vitamin A can interact with some antibiotics. Taking very large amounts of vitamin A along with some antibiotics can increase the chance of a serious side effect called intracranial hypertension. But taking normal doses of vitamin A along with tetracyclines doesn't seem to cause this problem. Do not take large amounts of vitamin A if you are taking antibiotics.

Some of these antibiotics include demeclocycline (Declomycin), minocycline (Minocin), and tetracycline (Achromycin).

Medications that can harm the liver (Hepatotoxic drugs)
Taking large amounts of vitamin A might harm the liver. Taking large amounts of vitamin A along with medications that might also harm the liver can increase the risk of liver damage. Do not take large amounts of vitamin A if you are taking a medication that can harm the liver.

Some medications that can harm the liver include acetaminophen (Tylenol and others), amiodarone (Cordarone), carbamazepine (Tegretol), isoniazid (INH), methotrexate (Rheumatrex), methyldopa (Aldomet), fluconazole (Diflucan), itraconazole (Sporanox), erythromycin (Erythrocin, Ilosone, others), phenytoin (Dilantin), lovastatin (Mevacor), pravastatin (Pravachol), simvastatin (Zocor), and many others.

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

Are there interactions with herbs and supplements?

Iron

Red blood cells need iron to make hemoglobin, the chemical that carries oxygen through the body. Taking vitamin A seems to improve hemoglobin levels in people who have low levels of iron and vitamin A.

Are there interactions with foods?

Fatty foods
Eating fatty foods helps the body absorb vitamin A.

What dose is used?

Adequate Intake (AI) levels of vitamin A for infants have been established: birth to 6 months, 400 mcg/day (1300 units); 7 to 12 months, 500 mcg/day (1700 units).

Recommended Dietary Allowance (RDA) levels for children and adults have been established: children 1 to 3 years, 300 mcg/day (1000 units); 4 to 8 years, 400 mcg/day (1300 units); 9 to 13 years, 600 mcg/day (2000 units); men 14 years and older, 900 mcg/day (3000 units); women 14 years and older, 700 mcg/day (2300 units); pregnancy 14 to 18 years, 750 mcg/day (2500 units); 19 years and older, 770 mcg/day (2600 units); lactation 14 to 18 years, 1200 mcg/day (4000 units); 19 years and older, 1300 mcg/day (4300 units). Tolerable Upper Intake Levels (UL) for vitamin A have also been established. The UL is the highest level of intake that is likely to pose no risk of harmful effects. The ULs for vitamin A are for preformed vitamin A (retinol) and do not include provitamin A carotenoids: infants and children from birth to 3 years, 600 mcg/day (2000 units); children 4 to 8 years, 900 mcg/day (3000 units); 9 to 13 years, 1700 mcg/day (6000 units); 14 to 18 years (including pregnancy and lactation), 2800 mcg/day (9000 units); adults age 19 and older (including pregnancy and lactation), 3000 mcg/day (10,000 units).

Vitamin A dosage is most commonly expressed in units, but dosage in micrograms is sometimes used.

Eating 5 servings of fruits and vegetables per day provides about 50% to 65% of the adult RDA for vitamin A.

Other names

3-Dehydroretinol, Antixerophthalmic Vitamin, Axerophtholum, Dehydroretinol, Fat-Soluble Vitamin, Oleovitamin A, Retinoids, Retinol, Rétinol, Retinol Acetate, Retinol Palmitate, Retinyl Acetate, Retinyl Palmitate, Vitamin A Palmitate, Vitamin A1, Vitamin A2, Vitamina A, Vitamine A, Vitaminum A.