Vitamin A Deficiencies
Vitamin A is a generic term for a number of compounds: retinol, retinal, retinoic acid (known as preformed Vitamin A) and a large number of carotenoids, the best-known being beta-carotene (known as preformed Vitamin A).
Basic function of Vitamin A
Vitamin A in the form of retinol plays a vital role in vision, specifically in the ability to adapt to the transition from light to dark. An inadequate amount of retinol available to the retina results in what is known as night blindness. Vitamin A also plays a role in maintaining a healthy immune system.
Vitamin A and food sources:
A wide variety of foods are excellent sources of Vitamin A: eggs, butter, milk (whole milk or reduced fat, fortified with Vitamin A), sweet potatoes, carrots, cantaloupe, mangoes, spinach and broccoli.
Vitamin A as a supplement:
Not all sources of Vitamin A offer the same potency, and they are absorbed differently by the body. For example it takes more beta-carotene, either in dietary or supplement form, to be converted into the biologically usable form of retinol. But with preformed Vitamin A, it is a 1:1 conversion to a usable form of retinol.
Vitamin A dosage:
The RDA (Recommended Dietary Allowance) for Vitamin A is expressed in both micrograms (mcg) and International Units (IU). For adult males age 19 and over, the amount is 900 micrograms, or 3,000 IU. For females age 19 and over, it is 700 mcg or 2,333 IU.
Vitamin A overdose/toxicity/interaction:
Vitamin A toxicity is caused by too much of the vitamin, not too much carotenoids. Acute toxicity is uncommon, but symptoms include nausea, fatigue, loss of appetite, dry skin, bone and joint pain. Long-term toxicity may cause liver damage. Signs of toxicity are generally seen when long-term consumption reaches 8,000-10,000 mcg/day. Upper levels of tolerance have been established at no more than 3,000 mcg/day (10,000 IU) for adults age 19 and older.
The risk of Vitamin A toxicity increases for those using the acne medication Accutane, the cancer drug Bexarotene and the psoriasis drugs acitretin and etretinate.
Vitamin A deficiencies:
In developing nations, Vitamin A deficiency is the leading preventable cause of childhood blindness. Mild Vitamin A deficiencies can cause dry eye, corneal ulcers and scarring . Vitamin A deficiency can also result in diseases of the immune system, respiratory and gastric illnesses.
Vitamin A benefits:
Studies have shown there may be benefits to using Vitamin A to reduce carcinogens for certain types of cancers, particularly breast, liver, colon and prostate cancers. Vitamin A is already being used to treat skin diseases (such as psoriasis and acne) and retinitis pigmentosa (progressive night blindness and loss of peripheral and central vision).