DR MARK J. WINTER / SCIENCE PHOTO LIBRARY DR MARK J. WINTER / SCIENCE PHOTO LIBRARY
Vitamin A. Molecular model of the retinal form of vitamin A. Retinal is one of three forms of vitamin A; the other two are retinol and retinoic acid. The chemical formula for retinal, also called retinene, is C20.H28.O. Atoms are represented as spheres and are colour-coded: carbon (blue), hydrogen (gold) and oxygen (red). Retinal is found in the light-sensitive cells of the retina inside the eye and is important for night vision. Vitamin A also plays an important role in maintaining a healthy reproductive system and healthy skin and mucous membranes. It is found in fruit, vegetables and some animal products. Vitamin A deficiencies can cause night blindness and slow growth. Excessive doses can be toxic, possibly leading to fatal liver failure.
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