2. Vitamin B2, also called riboflavin, is widely distributed. After being absorbed from food, it can be transformed into flavin mononucleotide under the action of riboflavin kinase in small intestinal mucosa, and further catalyzed by pyrophosphorylase in somatic cells to produce flavin adenine dinucleotide. Flavin adenine dinucleotide and flavin mononucleotide are the active forms of vitamin B2. Vitamin B2 is an auxiliary group of oxidoreductases in vivo, such as succinate dehydrogenase, xanthine oxidase and NADH dehydrogenase, which mainly acts as a hydrogen transporter. When human beings lack vitamin B2, bursitis, blepharitis, angular stomatitis and cheilitis will occur, so we should pay attention to vitamin B2 supplementation.