Vitamin A helps maintain the structural and functional integrity of mucous membranes of the gastrointestinal and genitourinary tracts. The vitamin helps keep the mucous membranes moist.
Vitamin A helps maintain eye function and skin integrity. Since vitamin A is necessary for eyes to adjust to light changes, night blindness is an indication of vitamin A deficiency.
Vitamin A supplementation is indicated for patients with dietary deficiency. Since vitamin A helps the eyes adapt to dim lighting, night blindness is usually the first indication of deficiency. Other symptoms of deficiency include skin lesions and dysfunction of mucous membranes. The patient may develop dry, thickened conjunctiva known as xerophthalmia. Deficiency may cause corneal degeneration known as keratomalacia, which is a keratinization of the corneal epithelium. Severe vitamin A deficiency may lead to blindness.
Certain forms of vitamin A are indicated to help treat skin disorders such as acne and keratosis follicularis. Vitamin A maintains skin structure by helping skin cells mature.
Hypervitaminosis A is a toxic state caused by excessive intake of vitamin A. Intoxication affects multiple organ systems. Symptoms include hepatosplenomegaly, jaundice, skins changes, and increased intracranial pressure. Symptoms of toxicity will disappear after removing the source of vitamin A.
Excessive amounts of vitamin A may lead to liver injury. Since the liver is responsible for breaking down bilirubin, jaundice may occur. Patients with excessive levels of vitamin A may develop other skin changes.
Since vitamin A is a fat soluble vitamin, excessive levels will accumulate in the body leading to hypervitaminosis A. Excessive amounts of vitamin A may lead to increased intracranial pressure (refer to the Picmonic on "Increased Intracranial Pressure Assessment"). The patient may experience nausea, vomiting, and papilledema as the optic disc swells in response to increased intracranial pressure.
Vomiting may occur in patients with excessive vitamin A intake. Since vitamin A helps maintain the gastrointestinal mucosa, the patient may experience nausea, anorexia, and abdominal pain.
Vitamin A is highly teratogenic and should not be supplemented in pregnant women. Excessive intake of vitamin A during pregnancy may cause malformation of the fetal skull and heart. Normal dietary intake of vitamin A does not lead to teratogenic effects.
Preformed vitamin A, or retinol, is only found in food products of animal origin. Dietary sources include dairy products, meats, fish oil, and fish. The body absorbs animal sources of vitamin A better than non-animal sources.
Provitamin A carotenoids are found in darkly colored green and carotene-rich or orange fruits and vegetables. Rich dietary sources include carrots, mangoes, cantaloupes, tomatoes, pumpkin, and sweet potatoes. Cells found in the intestinal mucosa convert provitamin A carotenoids into retinol. However, compared with retinol found in animal products, sources of dietary carotenoids are less absorbed.
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