Functions

Essential for normal growth, tissue growth and maintenance, night vision, healthy eyes, and normal bone and tooth development, although molecular functions are not well known.

Vitamin A helps maintain epithelial integrity, which is useful in skin complaints and in skin and wound healing (with Zinc) as well as maintaining a health mucous membrane (lining of nose, throat, gut). Vitamin A also provides lysosome stability. Vitamin A is involved in the photoreceptors of the retina, particularly in rhodopsin formation.

Stores of Vitamin A are depleted in infectious disease. Vitamin A is considered to be essential to protecting against infection by augmenting many immune functions including antibody response and white blood cell activity.

Vitamin A is an antioxidant and is thought to be useful in protecting the body against damage from free radicals that may contribute to disease.

Uses

Vitamin A is essential to good immunity. It may be useful in iron-deficiency anemia (increases Fe metabolism). Vitamin A may be useful in PMS, menorrhagia, lupus colitis, and ulcers. It may be useful in cases of trauma, stress, alcohol use and smoking.

Vitamin A may be preventive of cancer, lung disease, skin disorders, eye disorders

Deficiency

Deficiency symptoms:

Night blindness

Perifolicular hyperkeratosis - small bumps around hair follicles

Xerophthalmia - corneas become ulcerated and swollen

Keratomalacia - thickening of the bone shaft

Decreased immunity

Allergies

Loss of tooth enamel, gum disease

Increased respiratory infections

May cause hypothryroid state

Abnormal function of gastrointestinal and genitourinary tracts

Symptoms of deficiency are more common amonst those with trouble absorbing fats, including those with pancreatitis, celiac disease and cytic fibrosis. Alcoholics are also at risk.

Dependent Nutritional Factors

Vitamin A is involved in iron absorption metabolism and storage. It is also necessary for the metabolism of calcium.

Co-factors

The presence of fat and bile is required for vitamin A absorption before transport to the liver. (The liver stores 90% of the body's vitamin A.)

Drug Interactions

Absorption of vitamin A is reduced by mineral oil laxatives, antacids, colchicine (anti-gout drug), and cholesterol reducing drugs.

Dose

Required Daily Amount (in international units)

(4,000 IU = 1,000 RE - retinol equivalents)

4,000-5,000 adult

2,000-4,000 kids

1,400-2,000 infants

Therapeutic dose (to treat a certain condition) is much higher. The RDA is based on how much is needed to prevent xeropthalmia.

Toxicity

Overdose of Vitamin A may cause:

Headache

Fatigue

Skin peeling

Hepatosplenomegaly

Bone pain, thickening

Constipation

Dry skin

Restlessness

Alopecia

Night sweats

NauCheilosis

Nausea and vomiting

Visual problems

Brittle nails

Bulging fontanelle (kids);

Carotenemia

Contraindicated in glaucoma; renal insufficiency; liver disease; gouty arthritis; pregnancy (thought to be teratogenic). Stopping the dose will usually reverse symptoms in adults; damage in children may be permanent.

Sources

Foods containing Vitamin A include:

Fish liver oils

Animal fats

Liver

Egg yolk

Apricots

Cantaloupe

Peaches

Carrots

Yellow and Dark Green leafy vegetables

Note that vitamin A is found as pre-formed Vitamin A (retinol/retinal) in animal products, and that it is found as pro-vitamin A in plant pigments called carotenes, which means that the body must convert it to active form.