Vitamin A is a group of unsaturated nutritional organic compounds, that includes retinol, retinal, retinoic acid, and several pro vitamin A carotenoids, among which beta-carotene is the most important. Wikipedia
Vitamin A Overview
Vitamin A, a fat-soluble vitamin, plays an important role in bone growth, reproduction, immune function, hormone synthesis and regulation, and vision. Your eyes need vitamin A to help them convert light into brain signals that allow you to perceive images. Vitamin A works to protect you against infection by helping create healthy white blood cells and by promoting healthy skin. Vitamin A helps cells divide and develop into specialized cells, like blood cells, lung cells, brain cells and other distinct tissues.
Best Food Sources
Preformed vitamin A (a.k.a. retinol) is found in foods of animal origin, such as liver, eggs, milk fortified with vitamin A, fortified cereals and fish. Green leafy vegetables and orange vegetables and fruits supply vitamin A in the form of carotenoids. To easily meet your recommended intakes, the Dietary Guidelines for Americans suggests 3 cups per week of dark leafy green vegetables and 2 cups per week of orange vegetables. Also, you need to understand that you can get vitamin A from animal or plant sources and that these sources are treated differently by the body. Vitamin A from animal foods, supplements and fortified foods is called “preformed vitamin A,” or retinol. Preformed vitamin A is in a form that is highly available to your body. Vitamin A from plant sources comes in the form of carotenoids, primarily beta carotene. To account for the absorption of different forms of vitamin A, scientists created a unit called retinol activity equivalent (RAE). For example, 12 micrograms (mcg) of beta carotene equals 1 mcg of retinol. To complicate matters, nutrition and supplement labels don’t use RAEs; instead they use International Units (IU). We’ve done the conversions for you.