Vitamin A stimulates the production of mucous, and is absorbed by the body 3-5 hours after ingestion. 1 Vitamin A is essential in the conversion of cholesterol into female estrogens and male androgens. Thyroxine, a thyroid hormone, stimulates the conversion of carotene into a usable nutrient, fat-splitting enzymes and bile salts convert carotene. An adequate supply of zinc is needed so that the liver can mobilize vitamin A out of its storage depots. A and E help increase sperm count, energizes immune system, works with the immune system to inhibit cells transformed by viruses.
Carcinogens remain more active when there is a vitamin A deficiency.
2 Prolonged excessive intake will result in bone fragility, thickening of long bones, deep bone pain, enlargement of liver and spleen, blurred vision, skin rashes, reduced thyroid activity, abnormalities in skin, eyes, and mucous membranes. If toxicity is detected, the symptoms will disappear in a few days after the vitamin is withdrawn. Abdominal pain, anorexia, bone pain, arthralgia, weakness, drying skin, cracking lips, fever, hair loss, headache, premature closure of epiphyses, polyuria, increased sensitivity of skin to light, irritability, vomiting, yellow-orange patches on soles of feet, palms of hands or skin around the nose and lips. Intake of polyunsaturated fatty acids with carotene result in rapid destruction of carotene unless antioxidants are present. Diabetics may not be able to convert carotene into provitamin A. Gastrointestinal and liver disorders, infections and any condition in which the bile duct is obstructed may limit the body's capacity to retain and use vitamin A. A low fat diet, resulting in little bile reaching the intestine, can cause vitamin A and carotene to be lost in the feces.