What it does: Vitamin A is the name of a group of fat-soluble retinoids, which are involved in immune function, vision, reproduction, and cellular communication. Vitamin A is critical for function in the retinal receptors, as well as for the outer surface of the eye. Vitamin A also supports cell growth playing a critical role in the normal formation and maintenance of the heart, lungs, kidneys, and other organs.
• Dietary sources: fish liver oils, egg yolks, green leafy, orange & yellow vegetables.
• Night blindness: early sign of Vitamin-A deficiency. May progress to xerophthalmia, which is dryness & ulceration of the cornea. May progress to blindness.
• See decrease in heath and integrity of skin.
• Deficiency is rare. Cystic fibrosis patients need supplementation.
Adverse effects: dry mucus membranes, cracked lips, yellowing of skin, fatigue, nausea, hair loss, headache, dizziness, blurred vision, birth defects, loss of muscular coordination, dry scaly skin.
• Multivitamin supplements typically contain 2,500–10,000 IU vitamin A, often in the form of both retinol and beta-carotene.
• Excess Vitamin-A supplementation: leads to dizziness, nausea, headaches, skin irritation, pain in joints and bones, coma, and even death.
Smokers should avoid Vitamin-A supplements. Taking beta-carotene seems to increase the risk of lung cancer in people who smoke (especially those smoking more than 1 pack per day), former smokers, asbestos exposure, and those who use alcohol (one or more drinks per day) in addition to smoking. Beta-carotene from the diet does not seem to have this adverse effect.
Random fact: polar bear liver is toxic and can cause death if consumed. Adverse effects occur when 25,000 to 33,000 units are ingested. One pound of polar bear liver — a fist-sized chunk and barely a meal — can contain 9 million units of vitamin A!