History In 1913, vitamin a was found in fish liver oil or yolk In 1931, retinol was isolated in mammal and salt water fish, which was called vitamin A Afterward 3-dehydroretinol was isolated in fresh water fish, which was called vitamin A2 、CH3 CH3 CH3 H3C CH OH CH3 CH3 Vitamin a2 Vitamin alHistory • In 1913, vitamin A was found in fish liver oil or yolk. • In 1931, retinol was isolated in mammal and salt water fish, which was called vitamin A1 . • Afterward, 3-dehydroretinol was isolated in fresh water fish, which was called vitamin A2 . H3C CH3 CH3 OH CH3 CH3 Vitamin A1 H3C CH3 CH3 OH CH3 CH3 Vitamin A2