Vitamin A

Vitamin A is vitamin in vegetables and dairy products, a fat-soluble vitamin found in some vegetables, fish, milk, and eggs, and important for vision. It is also known as retinol and carotenoids. There are many reasons why vitamin A is so important to the immune system. Vitamin A helps to maintain the function of the cells that line the airways, digestive tract, and urinary tract, this is important because these paths are lined with mucosal cells that act as a barrier to germs. Without sufficient vitamin A, these cells would not function properly. Vitamin A is also important to maintaining a healthy immune system, as it is integral to white blood cell production. Both vitamin A excess and deficiency are known to cause birth defects. Retinol and retinoic acid are essential for embryonic development. During fetal development, retinoic acid functions in limb development and formation of the heart, eyes, and ears

Deficiency in Vitamin A
A deficiency of vitamin A can have damaging effects on your vision as well as your susceptibility to infectious diseases. Vitamin A is readily available and, in industrial nations, deficiencies in it are very rare, except in poor country we still can find it. A severe vitamin A deficiency can result in corneal ulcers, scarring, and blindness. In its mildest forms, vitamin A deficiencies can lead to poor night vision. Resistance to infectious diseases is also linked to insufficient intake of vitamin A. Children who are even mildly deficient in vitamin A are more susceptible to respiratory disease and diarrhea.

Hypervitaminosis A
Hypervitaminosis A is the condition caused by vitamin A toxicity. It is caused by overconsumption of preformed vitamin A, not carotenoids. Acute vitamin A toxicity is relatively rare, and symptoms include nausea, headache, fatigue, loss of appetite, dizziness, dry skin, and cerebral edema. Signs of chronic toxicity include dry itchy skin, desquamation, loss of appetite, headache, cerebral edema, and bone and joint pain. Also, symptoms of vitamin A toxicity in infants include bulging fontanels.Severe cases of hypervitaminosis A may result in liver damage, hemorrhage, and coma. Generally, signs of toxicity are associated with long-term consumption of vitamin A in excess of ten times the RDA (8,000 to 10,000 mcg/day or 25,000 to 33,000 IU/day).