Vitamin A plays an important role in vision, bone growth, reproduction and cell division. Vitamin A helps regulate the immune system by making white blood cells that destroy harmful bacteria and viruses. Vitamin A also may help a type of white blood cell called lymphocytes fight infections more effectively.

Vitamin A promotes healthy surface linings of the eyes the respiratory, urinary and intestinal tracts. When those linings break down, it becomes easier for bacteria to enter the body and cause infection. Vitamin A also helps the skin and mucus membranes function as a barrier against bacteria and viruses.

There are two categories of vitamin A. Preformed Vitamin A is found in foods that come from animals. It is absorbed in the form of retinol, one of the most usable forms of vitamin A. Sources include milk, liver and some fortified food products.

Vitamin A is also found in fruits and vegetables and is called provitamin A carotinoid. Common provitamin A carotenoids found in foods that come from plants are beta-carotene and alpha-carotene. Beta-carotene is most efficiently made into retinol . Alpha-carotene is also converted to vitamin A, but only half as efficiently as beta-carotene. There are 563 identified carotenoids and fewer than 10% can be made into vitamin A in the body.

Some provitamin A carotenoids have been shown to function as antioxidants and protect cells from free radicals, which are potentially damaging by-products of oxygen metabolism.