Food Supplements and Vitamins. Vitamin A (retinol)

vitaminA_2

Background

Vitamin A is a fat-soluble vitamin that is derived from two sources: preformed retinoids and provitamin carotenoids. Retinoids, such as retinal and retinoic acid, are found in animal sources such as liver, kidney, eggs, and dairy produce. Carotenoids, such as beta-carotene (which has the highest vitamin A activity), are found in plants such as dark or yellow vegetables and carrots.

Natural retinoids are present in all living organisms, either as preformed vitamin A or as carotenoids, and are required for biological processes such as vision and cellular growth. A major biologic function of vitamin A (as the metabolite retinal) is in the visual cycle. Research also suggests that vitamin A may reduce the mortality rate from measles, prevent some types of cancer, aid in growth and development, and improve immune function.

Recommended dietary allowance (RDA) levels for vitamin A oral intake have been established by the U.S. Institute for Medicine of the National Academy of Sciences to prevent deficiencies in vitamin A. At recommended doses, vitamin A is generally considered nontoxic. Excess dosing may lead to acute or chronic toxicity.

Vitamin A deficiency is rare in industrialized nations but remains a concern in developing countries, particularly in areas where malnutrition is common. Prolonged deficiency can lead to xerophthalmia (dry eye) and ultimately to night blindness or total blindness, as well as to skin disorders, infections (such as measles), diarrhea, and respiratory disorders.

Dosing

NB! The below doses are based on scientific research, publications, traditional use, or expert opinion. Many herbs and supplements have not been thoroughly tested, and safety and effectiveness may not be proven. Brands may be made differently, with variable ingredients, even within the same brand. The below doses may not apply to all products. You should read product labels, and discuss doses with a qualified healthcare provider before starting therapy.

Adults (18 years and older)

Vitamin A is found in dairy products, fish, and darkly colored fruits and vegetables. Consumption of five servings of fruits and vegetables daily supplies 5-6 milligrams daily of provitamin A carotenoids, which provides about 50-65% of the adult recommended dietary allowance (RDA) for vitamin A.

Vitamin A is included in most multivitamins, often in 5000 IU doses as softgels, capsules, tablets, or liquid. U.S. RDAs for adults have been established by the U.S. Institute of Medicine of the National Academy of Sciences. The recommendations are as follows: 900 micrograms daily (3000 IU) for men and 700 micrograms daily (2300 IU) for women. For pregnant women 19 years old and older, 770 micrograms daily (2600 IU) is recommended. For lactating women 19 years old and older, 1300 micrograms daily (4300 IU) is recommended.

  • For vitamin A deficiency not involving xerophthalmia, the following has been used: 100,000 IU by mouth or injected into the muscle daily for three days, followed by 50000 IU daily for two weeks. A maintenance dose of 10,000-20000 IU daily for two months has been recommended.
  • For community-based in intervention, 200000 IU has been taken as a single dose by mouth monthly for six months.
  • For acute promyelocytic leukemia (treatment), all- trans retinoic acid (Vesanoid® (tretinoin)) has been administered as follows: 45 milligrams per square meter of body surface area daily by mouth, as two evenly divided doses until complete remission; therapy should be discontinued 30 days after the achievement of complete remission or after 90 days of treatment, whichever occurs first.
  • For HIV, vitamin A (400,000 IU in adults and 50000 IU in infants) has been given to women and infants by mouth during the postpartum period for two years.
  • For mortality reduction, 1333-200000 IU has been taken by mouth daily or on alternate days for 28 days to 12 years.
  • For oral leukoplakia, 300000 IU has been taken by mouth weekly for 12 months or 200,000 IU has been taken by mouth weekly for six months or 1-2 milligrams of 13- cis -retinoic acid per kilogram of body weight has been taken by mouth daily for three months. Topical 0.1% isotretinoin gel three times daily for four months or a topical formulation of 20 milligrams of acitretin daily in a two-layer mucoadhesive tablet has been used.
  • For retinitis pigmentosa, the National Eye Institute (NEI) recommends that patients with typical forms receive 15000 IU of supplemental vitamin A palmitate daily under medical supervision.
  • For tuberculosis, 5000-200000 IU has been taken three times by mouth prior to antituberculosis medication.
  • For UV-induced skin damage, topical all- trans retinoic acid (tretinoin, the acid form of vitamin A), at a concentration of 0.02% or higher, has been used over a period of 4-11 months.
  • Supporting care following chemotherapy may include weekly injections of 100,000 IU of vitamin A. Patients receiving vitamin A should be observed carefully for liver toxicity.

Injections should always be performed by a licensed healthcare provider.

Children (under 18 years old)

Recommended dietary allowances (RDAs) have been established by the U.S. Institute of Medicine of the National Academy of Sciences. The recommendations are as follows: for children 1-3 years old, 300 micrograms (1000 IU) daily; for children 4-8 years old, 400 micrograms (1300 IU) daily; and for children 9-13 years old, 600 micrograms (2000 IU) daily. For pregnant women 14-18 years old, 750 micrograms (2500 IU) daily is recommended. For lactating women 14-18 years old, 1200 micrograms (4000 IU) daily is recommended.

The World Health Organization (WHO) has established dosage guidelines for children 6-11 months old to receive 100000 IU of vitamin A. This increases to 200000 IU every six months from 12 to 59 months of age.

  • For anemia, 3000 micrograms of vitamin A has been taken by mouth daily for two months.
  • For bronchopulmonary dysplasia in premature infants, 2000 IU on alternate days to 4,000 IU three times weekly by mouth has been taken.
  • For childhood growth promotion, 60 milligrams of vitamin A has been taken for up to six months.
  • For cystic fibrosis, the 2002 cystic fibrosis guidelines recommend vitamin A supplements for all children with cystic fibrosis and pancreatic insufficiency, specifically 3000 micrograms of retinol activity equivalents (RAEs) daily for children over the age of eight years.
  • For infant mortality, the following has been taken: three milligrams by mouth daily from 18 to 28 weeks’ gestation; 7,000 micrograms by mouth once weekly during gestation; 5000-10000 IU daily by mouth from 12-24 weeks’ gestation; 200000 IU weekly, or 200000 IU at time of delivery; and 200000-400000 IU daily by mouth postpartum. A dose of 2000 IU has been taken every two days for 28 days, injected into the muscle of infants. Also injected into the muscle, 4000 IU every two days or 3750 IU every two days for 16 days has been used. Doses between 1500 and 5000 IU, by mouth or injected into the muscle of the infant, have been used every other day or three times weekly. Doses from 8333 IU weekly to 20,000 IU every six months by mouth have been used.
  • For malaria, children aged 6-60 months were given one capsule (or half a capsule if younger than 12 months) of 200000 IU of vitamin A (in 200 microliters of peanut oil with 10 micrograms of vitamin E as a preservative) every three months for 13 months.
  • For measles, the World Health Organization (WHO) recommends 200000 IU daily by mouth for two days for children with measles who live in areas of vitamin A deficiency. For infants with measles, the WHO recommends 100000 IU daily by mouth for two days.
  • For childhood mortality, does from 8333 IU weekly to 200000 IU every six months by mouth have been used. Doses from 10000 IU weekly for 40 weeks to 206000 IU once very four months, for up to six doses, have been used.
  • For HIV, a large dose of vitamin A (400000 IU in adults and 50,000 IU in infants) has been given to women and infants during the postpartum period for two years.
  • For xerophthalmia (dry eye), the World Health Organization (WHO) recommends 200000 IU daily by mouth immediately on diagnosis, 200000 IU on the following day, and then 200000 IU prior to discharge, or if clinical deterioration occurs, or 2-4 weeks later. Infants under 12 months of age and very small and very-low-weight children should be given half the dosage.

Safety

NB! There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.

Allergies

Avoid in individuals with a known hypersensitivity or allergy to vitamin A or any component of the formulation.

Side Effects and Warnings

Vitamin A is considered safe when consumed in recommended dietary allowances (RDAs). Adults who eat fortified foods with vitamin A, such as low-fat dairy products and a lot of fruits and vegetables, generally do not require supplements or multivitamins that contain vitamin A.

Adverse effects from vitamin A may include mouth ulcers, cracked lips, psoriasis flare-ups, cracked fingernails, sore eyes, scaling skin, hair loss, skin irritation, skin dryness, pain, and redness (topical analogs), as well as diarrhea, dyspepsia, steatosis (fatty change), perisinusoidal fibrosis (in the liver), chronic hepatitis, cirrhosis, transient fullness and bulging of the anterior fontanelle, cough, fever, respiratory infection, and increased risk of lung cancer, HIV transmission (through breastfeeding), and mortality.

Vitamin A toxicity, or hypervitaminosis A, is rare in the general population. Vitamin A toxicity can occur with excessive amounts of vitamin A taken over short or long periods of time. Consequently, toxicity can be acute or chronic. Symptoms of acute (short-term) toxicity include nausea, headache, fatigue, loss of appetite, dizziness, dry skin, desquamation (loss of skin), and cerebral edema (swelling in the brain). Symptoms of chronic (longer-term) toxicity include dry itchy and cracking skin, desquamation, dry lips, scaling anorexia, headache, psychiatric changes, cerebral edema, bone and joint pain, osteoporosis, and hip fracture. Severe toxicity can lead to eye damage, high levels of calcium, and liver damage. In children, signs of toxicity include irritability, drowsiness, dizziness, delirium, coma, vomiting, diarrhea, increased intracranial pressure with bulging fontanelles in infants, headache, swelling of the optic (eye) disk, bulging eyeballs, visual disturbances, and skin redness and peeling.

Persons with liver disease and high alcohol intake may be at risk for hepatotoxicity from vitamin A supplementation. Vitamin A toxicity may lead to intrahepatic cholestasis, a condition where bile cannot flow from the liver into the intestines. Treatment with ursodeoxycholic acid has been shown to greatly improve the symptoms of cholestasis.

  • Use cautiously in children and infants, as high-dose vitamin A has been shown to increase the risk of respiratory infection in preschool-aged children and infants less than one month of age.
  • Use cautiously in combination with bile acid sequestrants, oral contraceptives, mineral oil, neomycin, or orlistat, due to reduced absorption of vitamin A.
  • Use cautiously in combination with alcohol or anticancer agents, due to the potential for increased risk of adverse effects.
  • Vitamin A may increase the risk of bleeding. Avoid in patients with bleeding disorders or those taking drugs that may increase the risk of bleeding.
  • Avoid in combination with tetracycline antibiotics, hepatotoxic agents, or retinoids, due to the increased risk of toxic effects.
  • Avoid in patients with fat malabsorption syndromes, intestinal infections, severe protein energy malnutrition, liver disease, or type V hyperlipoproteinemia (a genetic disorder).
  • Smokers who consume alcohol and beta-carotene may be at an increased risk for lung cancer or cardiovascular disease. High-dose vitamin A and beta-carotene should be avoided in patients at high risk of lung cancer.
  • Avoid in individuals with a known hypersensitivity or allergy to vitamin A or any component of the formulation.

Pregnancy and Breastfeeding

Vitamin A should only be used within the recommended dietary allowance, because vitamin A excess, as well as deficiency, has been associated with birth defects. Excessive doses of vitamin A have been associated with central nervous system malformations.

Vitamin A is excreted in human breast milk. The benefits or dangers to nursing infants have not been clearly established.

source: http://www.mayoclinic.com

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