Vita A

Uses

Effective for:

• Vita A deficiency. Taking vitamin A by mouth is effective for preventing and treating symptoms of vitamin A deficiency. Vita 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:

• Breast cancer. Premenopausal women with a family history of breast cancer who consume high levels of vitamin A in their diet seem to have reduced risk of developing breast cancer. It is not known if taking vitamin A supplements has the same benefit.
• Cataracts. Research suggests that high intake of vitamin A in the diet is linked to a lower risk of developing cataracts.
• Diarrhea related to HIV. Taking vitamin A along with conventional medicines seems to decrease the risk of death from diarrhea in HIV-positive children with vitamin A deficiency.
• Malaria. Taking vitamin A by mouth seems to decrease malaria symptoms in children less than 3 years-old living in areas where malaria is common.
• Measles. Taking vitamin A by mouth seems to reduce the risk of measles complications or death in children with measles and vitamin A deficiency.
• Precancerous lesions in the mouth (oral leukoplakia). Research suggests that taking vitamin A can help treat precancerous lesions in the mouth.
• Recovery from laser eye surgery (photoreactive keratectomy). Taking vitamin A by mouth along with vitamin E seems to improve healing after laser eye surgery.
• Complications after pregnancy. Taking vitamin A seems to reduce the risk of diarrhea and fever after pregnancy in malnourished women.
• Complications during pregnancy. Taking vitamin A by mouth seems to reduce the risk of death and night blindness during pregnancy in malnourished women.
• Eye disease affecting the retina (retinitis pigmentosa). Research suggests that taking vitamin A can slow the progression of an eye disease that causes damage to the retina.

Vita A is also used to associated treatment for these conditions: Deficiency, Vitamin A, Deficiency, Vitamin D, Degenerative Retinal Disorders, Disorder of the Epithelium, Disorder of the Mesoderm, Inner ear disorder, Vitamin Deficiency, Vitamin E Deficiency, Nutritional supplementation

How Vita A works

Vision:Vita A (all-trans retinol) is converted in the retina to the 11-cis-isomer of retinaldehyde or 11-cis-retinal. 11-cis-retinal functions in the retina in the transduction of light into the neural signals necessary for vision. 11-cis-retinal, while attached to opsin in rhodopsin is isomerized to all-trans-retinal by light. This is the event that triggers the nerve impulse to the brain which allows for the perception of light. All-trans-retinal is then released from opsin and reduced to all-trans-retinol. All-trans-retinol is isomerized to 11-cis-retinol in the dark, and then oxidized to 11-cis-retinal. 11-cis-retinal recombines with opsin to re-form rhodopsin. Night blindness or defective vision at low illumination results from a failure to re-synthesize 11-cis retinal rapidly.
Epithelial differentiation: The role of Vita A in epithelial differentiation, as well as in other physiological processes, involves the binding of Vita A to two families of nuclear retinoid receptors (retinoic acid receptors, RARs; and retinoid-X receptors, RXRs). These receptors function as ligand-activated transcription factors that modulate gene transcription. When there is not enough Vita A to bind these receptors, natural cell differentiation and growth are interrupted.

Dosage

Vita A dosage

Vita A deficiency For severe deficiency with corneal changes: 500,000 unit/day for 3 days, followed by 50,000 unit/day for 2 wk and then 10,000-20,000 unit/day for 2 mth as follow-up therapy.

For cases without corneal changes: 10,000-25,000 unit/day until clinical improvement occurs (usually 1 -2 wk).

Side Effects

Hypervitaminosis A characterised by fatigue, irritability, anorexia, weight loss, vomiting and other Gl disturbances, low-grade fever, hepatosplenomegaly, skin changes, alopoecia, dry hair, cracking and bleeding lips, SC swelling, nocturia, pains in bones and joints.

Toxicity

Acute toxicity to vitamin A can occur when adults or children ingest >100x or >20x the RDA, respectively, over a period of hours or a few days. The RDA for vitamin A differs depending on age and sex and can range from 300 - 900 μg retinol activity equivalents (RAE) per day. Symptoms of acute systemic toxicity generally include mucocutaneous involvement (e.g. xerosis, cheilitis, skin peeling) and may involve mental status changes. Children are typically more susceptible to acute vitamin A toxicity - daily intakes of as little as 1500 IU/kg have been observed to result in toxicity.

Chronic vitamin A toxicity can develop following the long-term ingestion of high vitamin A doses. While there is a wide variation in the lowest toxic vitamin A dose, the ingestion of >25 000 IU daily for 6 years or 100,000 IU daily for 6 months is considered to be toxic. Chronic vitamin A toxicity can affect many organ systems and can lead to the development of osteoporosis and CNS effects (e.g. headaches).

Precaution

Cholestatic jaundice; fat-malabsorption conditions. Monitor patients closely for toxicity. Liver impairment and children.

Interaction

Decreased absorption with neomycin. Increased risk of hypervitaminosis A with synthetic retinoids eg, acitretin, isotretinoin and tretinoin. Increased risk of toxicity when used with alcohol.

Food Interaction

Elimination Route

Readily absorbed from the normal gastrointestinal tract

Half Life

1.9 hours

Pregnancy & Breastfeeding use

Pregnancy Category A. Adequate and well-controlled human studies have failed to demonstrate a risk to the fetus in the first trimester of pregnancy (and there is no evidence of risk in later trimesters).

Contraindication

Hypervitaminosis A; pregnancy (dose exceeding RDA).

Innovators Monograph

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