Vitamin A is known as retinol, a name given in reference to the participation of this compound in the functions of the retina of eyes. It has also been called the "anti-infective" vitamin due to its role in supporting the activities of the immune system. While retinol or preformed vitamin A occurs only in animal foods, fruits and vegetables that contain certain carotenoids, it can also provide vitamin A. The body can convert certain carotenoids like beta-carotene, alpha-carotene and gamma-carotene into vitamin A. These carotenoids are sometimes referred to as "provitamin A" and retinol as "preformed vitamin A".