Vitamin A is a fat-soluble vitamin that is necessary for cell growth and differentiation, bone growth, and reproduction. It is also important for maintaining the health of the respiratory, urinary, and intestinal tracts. Most people get plenty of vitamin A through their diet; supplementation is not considered necessary for the average person, but is helpful for people with a deficiency.
Vitamin A is the name for a group of closely related fat-soluble compounds. Vitamin A deficiency is rare in the United States, but is a common cause of blindness in developing countries. Although this vitamin is essential for many important functions of the body, taking too much can cause more harm than good.
(Click Benefits of Vitamin A for more information on what the vitamin is used for.)
Retinoids (such as retinol) are types of vitamin A that come from animal sources. They are the most readily usable forms of the vitamin. Carotenoids (such as beta-carotene) are types of vitamin A from plant sources. The body uses carotenoids to make retinol. Vitamin A is stored in the liver, and the liver helps maintain the proper blood levels of the vitamin.
Vitamin A is necessary for cell growth and differentiation (the process that makes stem cells into different types of cells), bone growth, reproduction, good vision, and a healthy immune system. It is important for maintaining the health of the lining of the respiratory, urinary, and intestinal tracts. It also helps control the genes for numerous different structural proteins, such as certain important proteins in the skin.
Most importantly, vitamin A is used for the transduction of light into nerve signals that are essential for vision.