Vitamin is an essential organic substance for human body, which cannot be synthesized by the body and must be supplied by food. Although it does not provide heat energy, does not constitute body tissues, and its content in food is very small. The human body only needs tens of milligrams or micrograms to meet the needs of the human body, but it is very important and must not be lacking. None of them can cause diseases. Therefore, scientists named it vitamin, which means essential for maintaining life. There are many kinds of vitamins, which can be divided into two categories according to solubility. One is water-soluble vitamins, including vitamin C and all B vitamins. The other is fat-soluble vitamins insoluble in water but soluble in fat, including vitamins A, D, E and K.