Vitamin A molecule. Computer model showing the structure of a molecule of the retinol form of vitamin A. Retinol is one of three forms of vitamin A; the other two are retinoic acid and retinal. It is obtained from the precursor beta-carotene that is found in fruit and vegetables, is found in animal products, and is itself a precursor to retinal. Retinal is important for night vision. Vitamin A also maintains a healthy reproductive system and healthy skin and mucous membranes. Deficiencies in vitamin A can lead to slow growth and night blindness. Excessive doses can be toxic, causing aches and pains and in some extreme cases liver failure and death. Atoms are represented as spheres and are colour-coded: carbon (grey), hydrogen (white), and oxygen (red) -