DR MARK J. WINTER / SCIENCE PHOTO LIBRARY DR MARK J. WINTER / SCIENCE PHOTO LIBRARY
Vitamin A. Molecular model of the retinol form of vitamin A. Retinol is one of three forms of vitamin A; the other two are retinoic acid and retinal. The chemical formula for retinol is C20.H30.O. Atoms are represented as balls and are colour-coded: carbon (blue), hydrogen (gold) and oxygen (red). Retinol, 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.
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